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Test Equipment Upcycling – Variable Attenuator Module

A while back I found myself in the need of an adjustable RF attenuator capable of high-GHz operation. As luck would have it I had an old Spectrum analyser on the shelf at work, which we had retired quite some time ago.

Spectrum analysers being quite capable test instruments, I knew that the input attenuation would be done with a standalone module that we could recover for reuse without too much trouble.

The attenuator module

Here’s the module itself, with the factory drive PCB removed from the bottom, showing the solenoids that operate the RF switches. There are test wires attached to them here to work out which solenoid switches which attenuation stage. In the case of this module, there are switches for the following:

  • Input select switch
  • AC/DC coupling
  • -5dB
  • -10dB
  • -20dB
  • -40dB

For me this means I have up to -75dB attenuation in 5dB steps, with optional switchable A-B input & either AC or DC coupling.

Drive is easy, requiring a pulse on the solenoid coil to switch over, the polarity depending on which way the switch is going.

Building a Control Board

Now I’ve identified that the module was reusable, it was time to spin up a board to integrate all the features we needed:

  • Onboard battery power
  • Pushbutton operation
  • Indication of current attenuation level

The partially populated board is shown at right, with an Arduino microcontroller for main control, 18650 battery socket on the right, and control buttons in the centre. The OLED display module for showing the current attenuation level & battery voltage level is missing at the moment, but it’s clear where this goes.

As there weren’t enough GPIO pins for everything on the Arduino, a Microchip MC23017 16-Bit I/O expander, which is controlled via an I²C bus. This is convenient since I’m already using I²C for the onboard display.

Driving the Solenoids

A closer view of the board shows the trip of dual H-Bridge drivers on the board, which will soon be hidden underneath the attenuator block. These are LB1836M parts from ON Semiconductor. Each chip drives a pair of solenoids.

Power Supplies

The bottom of the board has all the power control circuitry, which are modularised for ease of production. There’s a Lithium charge & protection module for the 18650 onboard cell, along with a boost converter to give the ~9v rail required to operate the attenuator solenoids. While they would switch at 5v, the results were not reliable.

Finishing off

A bit more time later, some suitable firmware has been written for the Arduino, and the attenuator block is fitted onto the PCB. The onboard OLED nicely shows the current attenuation level, battery level & which input is selected.

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Wheelchair Motor Service Part 1: Teardown & Inspection

Trolley Propulsion System: Wheelchair Motor Units

So it’s time to get the propulsion system underway for the trolley, a pair of wheelchair motors were sourced for this, from HacMan. Since I don’t know how many hours are on these units, or how they’ve been treated in the past, I’m going to do a full service on them to ensure reliability. I decided on wheelchair motors due to their extreme ruggedness & heavily built components – this project when complete is going to weigh in at about 150kg!
I suspected something was amiss with one of the motors from running them under no load: the left hand wheelchair motor was heating up to the point of being too hot to touch, so this one at the very least needed some investigation.

Motor Disassembly & Assessment

Rear Cover Removed
Rear Cover Removed

With the back cover removed from the motor the electromagnetic brake is revealed. This engages when power is removed to stop the motor freewheeling, which even though it’s a wormdrive box, it will do readily if backdriven.

Electromagnetic Brake Assembly
Electromagnetic Brake Assembly

The brake is rated 6.7W at 24v DC.

Brake Disc
Brake Disc

The brake disc is just visible between the plates of the brake here, with some green dust worn off the disc. When power is applied, the top disc, just under the magnet on top, is pulled upward against spring pressure away from the brake disc, which is attached to the motor armature.

Brake Disc
Brake Disc

Here’s the brake disc, removed from the motor. There’s only a little wear here, as I’d expect – these brakes don’t engage until the motors have come to a complete stop.

Brake Actuator
Brake Actuator

The steel disc above the magnet acts as one of the friction surfaces of the brake.

Brake Solenoid
Brake Solenoid

Finally, the solenoid is at the back, partially potted in resin. The strong coil spring in the centre applies the brakes when power is disconnected.

Gearbox Grok
Gearbox Grok

Removing the top of the gearbox reveals the state of the internals – There’s no wear at all on the gearset, but the lubricant is totally manky. The external oil seals have been leaking for some time, letting water in and grease out. The emulsified result is revolting! These gearboxes have a wormdrive first stage, the worm gear is underneath the left hand gearset. Steel spur gears then do the final gearing to the output shaft. The output gear is splined onto the output, and can slide along the shaft out of mesh – this is the freewheel clutch mechanism. At the moment it’s all obscured by the disgusting lubricant.

Input Shaft Seal
Input Shaft Seal

Here’s the failed seal on the left hand gearbox, the face damage was done by petrol immersion to clean everything up. (The seal is already compromised, so I’m not fussed about solvents eating the remaining rubber). The motor shaft is joined to the gearbox input by a rubber coupling.

Output Shaft Seal
Output Shaft Seal

The output shaft seals seem to be still OK, there has been some seepage past the collar that the shaft rides in, but nothing more. This can be resealed with some Loctite bearing sealant. The sleeve is held into the gearbox by the wheel hub when in operation, but this doesn’t seal the gap unfortunately. I don’t know why the manufacturer didn’t just machine the shaft to that larger diameter, instead of using an extra sleeve to accommodate the seal.

Bore Seals
Bore Seals

The bore seals covering the ends of the shafts are also fine, which is a good thing, since I can’t seem to find replacements for these anywhere. The input shaft seals will be replaced on both gearboxes though.

Motor Contamination
Motor Contamination

The oil seal must have been leaking for a long while! This is the gearbox end of the wheelchair motor frame, completely clogged with grease. Luckily only a small amount has made it down past the armature to the brushgear.

Damaged Commutator
Damaged Commutator

The commutator of this motor is badly damaged, and the brushes are very worn. This has been caused by the gearbox oil seal failing, and contaminating the motor internals with lubricant. The undercut between the segments is all but gone – filled with an abrasive mixture of brush dust, copper dust & old lubricant. Some repair work will be required here.

Second Motor
Second Motor

Here’s the brushgear removed from the second wheelchair motor, this one looks much more normal, and there’s not as much wear on the brushes or the commutator. Just the usual coating of brush dust.

Armatures
Armatures

Here’s both armatures together, with the contaminated one on the right, after some cleaning to remove most of the greasy old grok & brush dust from everything. The windings on the damaged left hand wheelchair motor haven’t darkened, which I would expect from severe overheating damage, so I’m hoping this armature is OK, and won’t require a rewind. Using an ohmmeter on these windings doesn’t tell me much – there’s only 7 turns of 0.86mm (20AWG) magnet wire in each coil, so they read as a dead short anyway. There was some leakage between the windings and the core before I cleaned things up – this was in the high (28+) megohms range, but this seems to have cleared now I’ve given things a real good cleaning.

More to come when new bearings & seals arrive!

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Aspen Universal Condensate Pump

Universal Peristaltic Condensate Pump
Universal Peristaltic Condensate Pump

Here’s another piece of commercial gear, from an industrial air conditioning unit. These pumps are used to drain the condensate from the evaporator unit, so water doesn’t end up raining down from the ceiling.

Pump Head
Pump Head

This is a peristaltic pump, with a silicone hose forming the pumping element.

Rear Panel
Rear Panel

The test switch & electrical connections are on the back, along with the data label.

Power & Sensor Socket
Power & Sensor Socket

The electrical connections are all on a single 5-pin socket. Along with 240v AC mains, there are a pair of thermistors connected to the unit, which switch the pump on when a 5°C temperature difference across the evaporator coil is detected. When air is cooled, it’s capacity for moisture drops, so the water condenses out on the coil.

Roller Wheel
Roller Wheel

Here the front cover has been removed from the pump, showing the silicone tube & roller wheel. The wheel was originally Cadmium-plated, but exposure to the elements has oxidized this into highly toxic Cadmium Oxide.

Pump Rollers
Pump Rollers

Here you can see the rollers. These pinch the tube at the inlet, and the rotation carries a slug of liquid through the tube to the outlet side.

Pump Tube
Pump Tube

Here’s the tube itself, the main wearing part of the pump. This is replaceable as a spare part.

Motor & Gearbox
Motor & Gearbox

Inside the casing is a shaded-pole motor, connected to a large gearbox, to give the slow rotation for the pump head. The rated speed is 51RPM.

Control PCB
Control PCB

There’s not much to the control PCB. The large resistor forms a voltage dropper, to reduce the mains 240v to a more suitable level for the logic. There’s a TL062C Low-Power JFET Op-Amp & a CD4060BCM 14-stage binary ripple counter forming the logic. The set point is adjustable via the potentiometer.

Pump Triac
Pump Triac

The pump motor is switched via this Z7M SMD triac, not much switching power is needed here as the motor is only a very small shaded-pole type.

Modular He-Ne Laser Power Supply

Description and Schematic

SG-HM2 is a modular He-Ne laser power supply based on IC-HI1 with some minor enhancements. The first version is for laser tubes up to approximately 1 mW (2 mW with trivial modifications) but it should be straightforward to go to 5 mW or even higher power tubes by replacing the SG-HM2 HV Module (HVM2-1) with one with a higher voltage and current rating, along with a higher power MOSFET and minor component value changes to the Control Module (suggestions below). I have added an adjustment for tube current, a current limiting resistor and Zener to protect against output short circuits, an enable input (ground to turn on), a bleeder resistor to virtually eliminate the shock hazard after the power supply is turned off, and power and status LEDs.

  • Get the schematic for SG-HM2 (1 mW version) in PDF format: [download id=”5610″]

Modifying SG-HM2 for Higher Power He-Ne Laser Tubes

The following are guidelines for modifying SG-HM2 to drive various power He-Ne lasers. The PCB layout below with two versions of the HV Module should accommodate He-Ne laser tubes up to 10 mW. All assume input of around 12 V though a higher power system can generally run lower power lasers at reduced input voltage. If operation at rated power on another input voltage is desired, the number of turns on the inverter transformer can be adjusted accordingly. As noted above, the 1 mW HV Module (HVM2-1) should run tubes up to about 2 mW, though increasing the µF values of some of the HV capacitors may be desirable to reduce ripple at the higher tube current. Minor changes may also be needed in the components on the SG-HM2 Control Module including using a higher power MOSFET for Q1 and reducing the values of R7 and/or R8 for the higher tube current. Or, just populate the Control Module with Q1 being an IRF644, R7 being 150 ohms, and R8 being 750 ohms for compatibility with all the HV modules. For that matter, the HVM2-5 PCB HV Module should be usable with lower power lasers.

   Laser Power       1 mW         2 mW         5 mW         10 mW
-----------------------------------------------------------------------
   Voltage           1200 V       1500 V       2300 V       3500 V
   Current           2-4mA        3-5mA        5-7mA        5-7mA

 SG-HM2 HV Module:

   PCB Version       HVM2-1       HVM2-1       HVM2-5       HVM2-5

   T101
    Core (DxH)       18x11 mm     18x11 mm     26x16 mm     26/16 mm
    Primary          9T,#28       9T,#28       9T,#26       9T,#26
    Secondary        450T,#40     450T,#40     600T,#40     900T,#40
     Res. (Est)      60 ohms      60 ohms      (90 ohms)    (120 ohms)

   D101-106          2kV          2kV          3kV          5kV

   C101-104          1nF,3kV      2nF,3kV      2nF,6kV      2nF,6kV
   C105              47pF,3kV     47pF,3kV     100pF,6kV    100pF,6kV
   C106              3nF,10kV     5nF,10kV     6nF,15kV     6nF,15kV

   R102              10K,1/2W     10K,1/2W     10K,1W       10K,1W
   R103              200M,10kV    200M,10kV    200M,15kV    200M,15kV 
   R106-107 (total)  10M          10M          15M          20M

 SG-HM2 Control Module:

   Q1              IRF630       IRF630       IRF640       IRF644
   R7              300          250          150          150
   R8              500          250          100          100

SG-HM2 Inverter Transformer

The inverter transformer for HVM2-1 is wound on a ferrite pot core with a small air-gap (about 0.005″). It is 18 mm in diameter by 11 mm high. While specified to use a 9 turn primary and 450 turn secondary, these values can be adjusted somewhat to handle various input and output requirements. Don’t go much lower on the primary as this may result in core saturation. The 9/450 transformer should be fine for 1 to 2 mW He-Ne laser tubes running on 8 to 15v DC input. With 9/300, it will operate on about 12 to 20v DC. Increasing the number of secondary turns (e.g., 9/600) may result in operation on a slightly lower input voltage, but probably not by much. The 9/450 transformer may even run He-Ne laser tubes larger than 2 mW but I haven’t yet tested this since I haven’t built a prototype of HVM2-5 as yet.

It doesn’t matter very much whether the primary (P) is wound first or the secondary (S) is wound first though the former appears to work slightly better, running the tube at about 8v DC input instead of 9v DC input for the same 9/450 transformer. P over S is slightly easier to wind since the primary doesn’t get in the way and increase the lumpiness of the secondary layers. However, with S over P, insulation is somewhat less critical since the HV lead is out away from anything else. With the P over S, additional insulation is needed between them. Also, since the primary coil is larger diameter, it will have more resistance and there will be greater inter-winding capacitance (though probably not significant). The secondary should be constructed as multiple layers of about 50 or 60 turns each, with insulating tape between layers. Each should be wound in as close to a single layer as possible with alternating layers staggered to prevent arc-over. This doesn’t have to be perfect but try to go gradually from one side to the other to keep wires at high relative potential away from each other. Make sure the HV output leads (particularly the one away from the dot) are well insulated as they exit the transformer. And, as noted, if the primary is over the secondary, there must be high voltage insulation between them. The peak output voltage when the MOSFET turns off (the flyback pulse) may be more than 5 times higher than what would be expected from the DC input voltage and the turns-ratio alone – several kV and this *will* try to find a path to ground! There are more detailed transformer construction instructions in the next section.

Note that this transformer is slightly larger physically than the one from IC-HI1. This is for two reasons: (1) It is easier to wind with more space and a larger wire size for the secondary, and (2) continuous operation should be possible with 2 mW laser tubes, which might have been marginal with the original transformer used in IC-HI1. A by-product of the larger core is that its 9 turn primary should be roughly equivalent to the 12 turn primary of the smaller core in terms of inductance and core saturation limitations.

Interestingly, a similar transformer found in a different commercial power supply, had no insulating tape anywhere. It would appear that with very precise machine-wound HV secondary, done first, the voltage is distributed so uniformly that this is unnecessary.

I’ve now built and tested several transformers in IC-HI1, removing the original transformer and installing socket pins so either the original or an adapter board can be plugged in. This setup is then equivalent to SG-HM2 with the HVM2-1 HV Module. The minimum input voltage values that follow are when driving a 0.5 mW He-Ne laser tube:

           Turns        Pot Core   Vin (VDC)
   ID   P/S    Order    (DxH mm)   Min  Max           Comments
 ------------------------------------------------------------------------------
   1* 12/600  S over P    14x8     7.5  15   Original IC-HI1 transformer
   2  12/350  S over P    18x11    14   22   First prototype, described above
   3   9/350  S over P    18x11    11   18   #2 with 3 P T added out-of-phase
   4   9/425  P over S    18x11     9   16
   5   9/450  P over S    18x11     9   16
   6   9/450  S over P    18x11     8   15
   7  12/500  P over S    26x16     8   15

*The number of turns on the original (#1) is not really known exactly and may be lower or higher by up to 25 percent based on the measured secondary resistance (45 ohms) and estimated wire size (somewhere between #38 and #40. (Even with the larger wire, the amount of bobbin area taken up by the wire is less than 50 percent so it should fit even with many layers of insulating tape. The transformer is Epoxy impregnated and likely to be impossible to disassemble into any form that can be analyzed!)

All of these transformers will drive He-Ne laser tubes of up to at least 2.5mW using the equivalent of the HVM2-1 HV Module which is part of IC-HI1. Even with the 2.5mW tube, the minimum operating voltage was only about 0.5v higher than for the 0.5mW tube. There is a good chance they would drive even larger He-Ne laser tubes (though possibly at a slightly higher input voltage) but I don’t dare try using the existing HV circuitry as it might not survive for long. I suspect that transformers #4, #5, and #6 would run on an input voltage of less than 8v DC but the salvaged cores I am using have a larger air-gap than might be optimal and I don’t have anything to reduce it without heavy losses. They attempt to start the tube at around 6v DC but are unable to maintain it and flicker rapidly. (#2 and #3, which use the same style core, would also benefit somewhat.) Operation using #1 and #5 is virtually identical, with the original running at perhaps 0.5v DC less input. I expect they would be even more identical if the air-gap on #5 were smaller, and #6 with its smaller air-gap does indeed run at the lower input voltage. I haven’t actually confirmed that anything blows up above the maximum voltages listed above, which were arbitrarily chosen. But I am guessing that bad things might happen at some point. 🙂

I have also constructed a transformer which will need to be used with HVM2-5: 12/1200, P over S, on a 30×19 pot core. I will also construct a 9/900. S over P, on a 30×19 pot core (or on a 26×16 if I can find one). Testing of these will have to await an HVM2-5 prototype.

SG-HM2 Transformer Construction

Here are details on construction of the inverter transformer for SG-HM2. With all parts and tools on hand, it takes about an hour start to finish. Only a small portion of this time is in the actual winding (at least if a coil winding machine is used). Most of the time is spent in adding the insulation tape and terminating the leads. After constructing a few of these, it does go quicker. 🙂

Step-by-step instructions are provided for the HVM2-1 transformer. The changes needed for HVM2-5 are summarized at the end of this section. Some sort of coil winding machine is almost essential as #40 wire is extremely thin and easy to break. (Anything larger than #40 will not fit on the bobbin.) It doesn’t have to be fancy. Mine is probably 50 years old of the type that is (used to be?) advertised in the back of electronics magazines. However, a couple of spindles – one that is fixed or free to rotate for the wire supply and the other which can be turned for the coil being wound – are really all that are needed. Don’t use any sort of powered approach though (unless you have a *real* professional coil winder!) as it is all too easy to break the wire if there is no tactile feedback to detect snags.

  1. Parts required for T101 of HVM2-1:
    • 18×11 mm (1811) ferrite pot core with a small air-gap (no more than 0.005″) or no air-gap, and a single section bobbin. These are available from several manufacturers but surplus or salvaged cores may be easier to obtain. Radio Shack used to have a “ferrite kit” which included a variety of sizes of cores (only 1 each though so you’d have to buy two kits and there were no bobbins!). I doubt the kit still exists though.
    • Approximately 1.5 feet of #28 magnet wire for the primary (9 turns wound first) and approximately 60 feet of #40 magnet wire for the secondary (450 turns wound on top of the primary). I found both these size wire in various solenoids and relays I’ve discombobulated. 🙂 Wire sizes aren’t critical but these are known to fit and the #40 can be handled with a reasonable chance of not breaking.
    • Sleeving to protect the primary wires where they leave transformer. I used approximately 2″ of insulation (each lead) from the individual wires in some 25 pair phone cable.
    • Wirewrap wire or other thin insulated wire to terminate the secondary wires where they leave the transformer.
    • Insulating tape. 1 mil Mylar or similar is desirable. However, I’ve found that thin clear (non-reinforced) packing tape does an adequate job, though it probably doesn’t have as much dielectric strength as real insulating tape so additional layers are required. It will also likely not stand up to overheating too well. Electrical tape is way too thick and would prevent enough turns from fitting.
    • A piece of Perf. board with holes on 0.1″ centers, 0.8″x0.8″. There should be 7 rows of holes each way so that one hole lines up in the center.
    • A Nylon 4-40 screw and nut to fasten the transformer to the board.
    • Four (4) machined-type IC socket pins or something similar to use as terminals.
  2. Wind the primary:
    • Slip a piece of sleeving over the start of the primary wire and position the sleeving so it extends about 1/2 turn inside the bobbin on the left side.
    • Wrap exactly 9 turns of this wire clockwise around the bobbin, left to right. The wires should enter and exit on the same angular position (slot) of the bobbin on opposite sides.
    • Slip another piece of sleeving over the wire end exiting the bobbin so that it too is about 1/2 turn inside the bobbin.
    • Wrap 1.5 to 2 turns of tape tightly over the primary winding to secure and insulate it.
  3. Wind the secondary:
    • Strip 1/8″ or so from the end of a 2″ piece of wire-wrap wire and solder the start of the wire for the secondary winding to it. Make sure the insulation on the fine magnet wire has been removed – usually just heating it while soldering will do this. Leave an inch or so of the magnet wire extending from the connection so that continuity can be confirmed with a multimeter, then snip it off. Install this in the opposite slot of the bobbin also on the left side with about 1/4″ of insulation inside the bobbin against the side and separated from the primary. Leave a little slack in the fine secondary wire so that slight motion won’t break it. Add a small piece of tape to protect and insulate this connection.
    • Using your coil winding machine (you do have one, correct?), build up the secondary in layers of about 50 to 75 turns in a counter-clockwise direction (bobbin being rotated clockwise). A single layer of wire won’t fit in the 1/8″ or so available (in the 18×11 mm core bobbin) so there will have to be some overlap. But, do this several times across the layer so that any given wire won’t be next to one with a much different voltage. In other words, wind a few turns and back up so that there will in essence be multiple sub-windings of 5 or 10 turns, repeated several times across the layer. Keep the wire at least 1/32″ away from either edge of the bobbin.
    • After each full layer or wire, add just over 1 layer of insulating tape making sure it covers the entire width of the bobbin. There should be just enough overlap to assure there is at least 1 layer of insulation but not much more as excessive tape will end up taking up too much space.The entire 450 turn winding will then require 6 to 9 full layers. Add another layer of insulating tape over the last winding layer leaving the wire end exposed.
    • Terminate the end of the secondary winding with another piece of thin wire by soldering as above. Confirm continuity with a multimeter. For the 450 turn secondary, the resistance should be about 60 ohms. Add a piece of thicker sleeving over this at the HV end if space is available. Else, use some bits of tape to insulate the wirewrap wire lead from the core and exposed inner layers that it may come near as it exits out the side of the bobbin. Add another layer of tape to secure the lead in place.
    • Add several more layers of insulating tape to complete the bobbin assembly.
  4. Prepare the mounting board:
    • Widen the center hole to 7/64″ to accommodate a 4-40 nylon screw.
    • Widen the holes at the 4 corners of the board to accept the 4 IC socket pins (if used) as a press-fit or glue them in place with 5 minute Epoxy or SuperGlue.
  5. Final assembly:
    • Install the ferrite pot core halves to the bobbin taking care not to crunch any of the wires. Orient it so that the primary and secondary leads are conveniently located with respect to the 4 pins, e.g., primary start: bottom left; primary end: top left, secondary start: bottom right; and primary end: top right.
    • Use the nylon 4-40 screw and nut to *gently* secure the transformer to the mounting board. The head of the 4-40 screw should be underneath the board. Don’t over-tighten or it may crack the core, especially if it has an air-gap in the middle.
    • Carefully remove the insulation from the ends of the wires. The secondary wires will still be fragile even with the wirewrap wire terminations. For the magnet wire, the easiest way to remove the insulation is to burn it off with a match or hot soldering iron and then clean with fine sandpaper.
    • Push the wires into their respective socket pins. (The wirewrap wires are too thin to be secure but they will make adequate contact for testing.)
    • Use a multimeter to confirm continuity of the primary (close to 0 ohms) and secondary (about 50 to 75 ohms).
  6. Testing:
    • Install the transformer in you HV Module. Attach a He-Ne laser tube and ballast resistor.
    • Power up on an variable DC power supply and check for reliable starting and stable operation. Adjust the core gap if needed. A smaller gap may result in more operating power available at a given input voltage. A larger gap will result in attempts to start on a lower input voltage. Somewhere around 0.005″ is probably a good compromise.
    • After testing the transformer (and adjusting the core gap if needed), use some adhesive to secure the pot core sections and to protect the transformer leads. Solder the leads into the socket pins.

The final result is shown on an adapter below:

Photo of SG-HM2 HVM2-1 Transformer being Tested in IC-HI1
Photo of SG-HM2 HVM2-1 Transformer being Tested in IC-HI1

The instructions for winding the HVM2-5 transformer are similar except for the dimensions, wire sizes and lengths, and number of turns for the primary and secondary:

  • Differences in parts list for T501 of HVM2-5 compared to T101 of HVM2-1:
    • 26×16 mm (2616) ferrite pot core with a small air-gap (no more than 0.005″) or no air-gap, and a single section bobbin.
    • Approximately 2.0 feet of #26 magnet wire for the primary (12 turns wound first) and approximately 75 to 120 feet of #40 magnet wire for the secondary (600 or 900 turns wound on top of the primary).
    • A piece of Perf. board with holes on 0.1″ centers, 1.0″x1.0″. There should be 9 rows of holes each way so that one hole lines up in the center.
    • A Nylon 10-32 screw and nut to fasten the transformer to the board.

Since the peak voltage on the HVM2-5 secondary may be 2 to 3 times higher than for HVM2-1, extra insulation and clearances will be required on the secondary.

SG-HM2 Printed Circuit Board Layout

A printed circuit board layout is also available. The Control Module is 2″x1.2″. The HV Modules are 3.6″x1.2″ and 4.5″x1.8″ for the 1 mW (HVM2-1) and 5 mW (HVM2-5), respectively. The Control and HV Modules are connected by a 2 pin cable for transformer drive and a 3 pin cable for current sensing from the laser tube. The two boards can easily be merged if desired.

The layout of the 3 PCBs may be viewed as a GIF file (draft quality) as below:

Sam's Modular He-Ne Laser Power Supply 2 PCB Layout
Sam’s Modular He-Ne Laser Power Supply 2 PCB Layout

.

A complete PCB artwork package for SG-HM2 (all PCBs on one sheet) may be downloaded in standard (full resolution 1:1) Gerber PCB format (zipped) as [download id=”5612″]

The Gerber files include the component side copper, soldermask, and silkscreen; solder side copper and soldermask, and drill control artwork. The original printed circuit board CAD files and netlist (in Tango PCB format) are provided so that the circuit layout can be modified or imported to another system if desired. The text file ‘sghm2.doc’ (in sghm2grb.zip) describes the file contents in more detail.

Note: The netlist does NOT include wiring for the HVM2-5 HV Module. Also, part numbers on the HVM2-5 PCB actually begin with a “5” instead of a “1” since Tango PCB will not allow duplicate part numbers on the same layout.

Magnets in High Power or Precision He-Ne Laser Heads

Effects of Magnetic Fields on He-Ne Laser Operation

If you open the case on a higher power (and longer) He-Ne laser head or one that is designed with an emphasis on precision and stability, you may find a series of magnets or electromagnetic coils in various locations in close proximity to the He-Ne tube. They may be distributed along its length or bunched at one end; with alternating or opposing N and S poles, or a coaxial arrangement; and of various sizes, styles, and strengths.

Magnets may be incorporated in He-Ne lasers for several reasons including the suppression of IR spectral lines to improve efficiency (such as it is!) and to boost power at visible wavelengths, to control its polarization, and to split the optical frequency into two closely spaced components. There are no doubt other uses as well.

The basic mechanism for the interaction of emitted light and magnetic fields is something called the ‘Zeeman Effect’ or ‘Zeeman Splitting’. The following brief description is from the “CRC Handbook of Chemistry and Physics”:

“The splitting of a spectrum line into several symmetrically disposed components, which occurs when the source of light is placed in a strong magnetic field. The components are polarized, the directions of polarization and the appearance of the effect depending on the direction from which the source is viewed relative to the lines of force.”

Magnetic fields may affect the behaviour of He-Ne tubes in several ways:

  • He-Ne tubes with long discharge paths will tend to amplify the (generally unwanted) IR wavelengths (probably the one at 3.39µm which is one of the strongest, if not the strongest of all lines) at the expense of the visible ones. The purpose of these magnets is to suppress spectral lines that do not contribute to the desired lasing wavelength (usually the visible red 632.8nm for these long tubes). As a result of the Zeeman Effect, if a gas radiates in a magnetic field, most of its spectral lines are split into 2 or sometimes more components. The magnitude of the separation depends on the strength of the magnetic field and as a result, if the field is also non-uniform, the spectral lines are broadened as well because light emitted at different locations will see an unequal magnetic field. These ‘fuzzed out’ lines cannot participate in stimulated emission as efficiently as nice narrow lines and therefore will not drain the upper energy states for use by the desired lines. The magnitude of the Zeeman splitting effect is also wavelength dependent and therefore can be used to control the gain of selected spectral lines (long ones are apparently affected more than short ones on a percentage basis).The Doppler-broadened gain bandwidth of neon is inversely related to wavelength. At 632.8nm (red) it is around 1.5 to 1.6 GHz; at 3,391nm (the troublesome IR line), it is only around 310MHz. A magnetic field that varies spatially along the tube will split and move the gain curves at all wavelengths equally by varying amounts depending on position. However, a, say, 100 or 200MHz split and shift of the gain curve for the 632.8nm red transition won’t have much effect, but it will effectively disrupt lasing for the 3,391nm IR transition.Without the use of magnets, the very strong neon IR line at 3.39µm would compete with (and possibly dominate over) the desired visible line (at 632.8nm) stealing power from the discharge that would otherwise contribute to simulated emission at 632.8 nm. However, the IR isn’t wanted (and therefore will not be amplified since the mirrors are not particularly reflective at IR wavelengths anyhow). Since the 3.39nm wavelength is more than 5 times longer than the 632.8 nm red line, it is affected to a much greater extent by the magnetic field and overall gain and power output at 632.8nm may be increased dramatically (25 percent or more). The magnets may be required to obtain any (visible) output beam at all with some He-Ne tubes (though this is not common).

    The typical higher power Spectra-Physics He-Ne laser will have relatively low strength magnets (e.g., like those used to stick notes to your fridge) placed at every available location along the exposed bore along the sides of the L-shaped resonator frame. They will alternate N and S poles pointing toward the bore. Interestingly, on some high mileage tubes, brown crud (which might be material sputtered off the anode) may collect inside the bore – but only at locations of one field polarity (N or S, whichever would tend to deflect a positive ion stream into the wall). The crud itself doesn’t really affect anything but is an indication of long use. And on average, tubes with a lot of brown crud may be harder to start, and require a higher voltage to run, and have lower output power.

    I do not know how to determine if and when such magnets are needed for long high power He-Ne tubes where they are not part of an existing laser head. My guess is that the original or intended positions, orientations, and strengths, of the magnets were determined experimentally by trial and error or from a recipe passed down from generation to generation, and not through the use of some unusually complex convoluted obscure theory. 🙂

    The only thing I can suggest other than contacting the manufacturer (like any manufacturer now cares about and supports He-Ne lasers at all!) is to very carefully experiment with placing magnets of various sizes and strengths at strategic locations (or a half dozen such locations) to determine if beam power at the desired wavelength is affected. Just take care to avoid smashing your flesh or the He-Ne tube when playing with powerful magnets. Though the magnets used in large-frame He-Ne lasers with exposed bores aren’t particularly powerful, to produce the same effective field strength at the central bore of an internal mirror He-Ne tube may require somewhat stronger ones, though even these needn’t be the flesh squashing variety. And, magnets that are very strong may affect other characteristics of the laser including polarization, and starting and running voltage. Enclosing the He-Ne tube in a protective rigid sleeve (e.g., PVC or aluminium) would reduce the risk of the latter disaster, at least. 🙂 If there is going to be any significant improvement, almost any arrangement of 1 or 2 magnets should show some effect.

    There may be an immediate effect when adding or moving a magnet. However, to really determine the overall improvement in (visible) output power and any reduction in the variation of output power with mode sweep, the laser should be allowed to go through several mode sweep cycles for 3.39 µm. These will be about 5.4 times the length of the mode sweep for 632.8 nm.

    CAUTION: For soft-seal laser tubes in less than excellent health (i.e., which may have gas contamination), changing the magnet configuration near the cathode may result in a slow decline in output power (over several hours) which may or may not recover. I have only observed this behaviour with a single REO one-Brewster tube, but there seems to be no other explanation for the slow decline to about half the original power, and then subsequent slow recovery with extended run time after the magnets were removed entirely. Possibly simply leaving the magnets in the new configuration would have eventually resulted in power recovery, but at the time the trend was not encouraging.

    (From: Lynn Strickland (stricks760@earthlink.net).)

    “They’ve pretty much nailed the 3.39 micron problem on red He-Ne tubes these days so magnets really aren’t needed on them. Even the new green tubes don’t have much of a problem – especially since the optic suppliers have perfected the mirror coatings. All of the good green mirrors are now done with Ion Beam Sputtering (IBS), as opposed to run-of-the-mill E-Beam stuff.However, you’ll probably see a benefit from magnets to suppress the 3.39µm line on the older He-Ne tubes.”

  • While most inexpensive He-Ne tubes that produce linearly polarized light do so because of an internal Brewster plate and lasers with external mirrors have Brewster windows on the ends of the plasma tube, it is also possible to affect the polarization of the beam with strong magnets again using the Zeeman Effect.Where the capillary of the plasma tube is exposed as with many older lasers, and the magnets can be placed in close proximity to the bore, their strength can be much lower. A few commercial lasers (like the Spectra-Physics model 132) offered a polarization option which adds a magnet assembly alongside the tube. In this case, what is required is a uniform or mostly uniform field of the appropriate orientation rather than one that varies as for IR spectral line suppression though both of these could be probably be combined. However, the polarization purity with this approach never came anywhere close to that using a simple Brewster window or plate, found in all modern polarized He-Ne lasers.Also see the section: Unrandomizing the Polarization of a Randomly Polarized HeNe Tube.
  • Two-frequency He-Ne lasers are used in precision interferometers for making measurements to nanometer accuracy. With these, the Zeeman effect is exploited to split the output of a single frequency He-Ne laser into a pair of closely spaced optical frequencies so that a difference or “split” frequency can be obtained using a fast photodiode. The most common are axial Zeeman lasers that use a powerful magnetic field oriented along the axis of the tube. For these, the “split” frequency is typically between 1.5 and 7.5 MHz (though it could be much lower but not much higher). Transverse Zeeman lasers use a moderate strength field oriented across the tube and have split frequencies in the 100s of kHz range. To stabilize these lasers, either a heater or piezo element is provided to precisely control cavity length.

In principle, varying fields from electromagnets could be used for intensity, polarization, and frequency modulation. I do not know whether any commercial He-Ne lasers have been implemented in this manner.

But if magnets were not originally present, the only situation where adding some may make sense is for older longer or “other colour” He-Ne tubes where a series of weak magnets may actually boost output power by 10 to 25 percent or more. On the other hand, most non-Zeeman stabilized He-Ne lasers do NOT like magnets at all. Even a relatively weak stray magnetic field from nearby equipment may result in a significant change in behaviour. However, unless ferrous metals are used in the laser’s construction, any change will likely not be permanent.

Typical Magnet Configurations

Here are examples of some of the common arrangements of magnets that you may come across. In addition to those shown, magnets may be present along only one side of the tube (probably underneath and partially hidden) or in some other peculiar locations. I suspect that for many commercial He-Ne lasers, the exact shape, strength, number, position, orientation, and distribution of the magnets was largely determined experimentally. In other words, some poor engineer was given a bare He-Ne tube, a pile of assorted magnets, a roll of duct tape, and a lump of modelling clay, and asked to optimize some aspect(s) of the laser’s performance. 🙂

  • Transverse (varying field) – These will most likely be permanent magnets in pairs, probably several sets.Polarity may alternate with North and South poles facing each other across the tube forming a ‘wiggler’ so named since such a they will tend to deflect the ionized discharge back and forth though there may be no visible effects in the confines of the capillary:
                       N      S      N      S      N      S      N
                 ||===================================================||
                 ||======. .=================================. .======||
                       S |||  N      S      N      S      N  |_| S
                         '|'                                 '|'
    
    

    For some including the Spectra-Physics 120, 124, 125, and 127, the magnets are actually below and on one side. The objective is usually IR (3.39µm) suppression and the magnets are generally relatively weak (refrigerator note holding strength). Alternatively, North and South poles may face each other:

                       N      S      N      S      N      S      N
                 ||===================================================||
                 ||======. .=================================. .======||
                       N |||  S      N      S      N      S  |_| N
                         '|'                                 '|'
    
    

    With either of these configurations, after long hours of operation, there may be very pronounced brown deposits inside the bore that correlate with the pole positions.

  • Transverse (uniform field). Here, the objective is to achieve a constant field throughout the entire discharge:
                       N      N      N      N      N      N      N
                 ||===================================================||
                 ||======. .=================================. .======||
                       S |||  S      S      S      S      S  |_| S
                         '|'                                 '|'
    
    

    This configuration is found in two very different situations. Strong magnets were used in laser like the Spectra-Physics 132P to polarize the beam. Weaker magnets are used in transverse Zeeman two-frequency He-Ne lasers.

  • Axial – These will most likely be permanent magnet toroids (similar to magnetron magnets), though an electromagnetic coil (possibly with adjustable or selectable field strength) could also be used. Thus, the North and South poles will be directed along the tube axis:
                            +--+      +--+      +--+      +--+
                          N |  | S  N |  | S  N |  | S  N |  | S
                            +--+      +--+      +--+      +--+
                ||======================================================||
                ||====. .========================================. .====||
                      |||   +--+      +--+      +--+      +--+   |_|
                      '|' N |  | S  N |  | S  N |  | S  N |  | S '|'
                            +--+      +--+      +--+      +--+
    
    

    Other axial configurations with opposing poles or radially oriented poles may also be used or there may be a single long solenoid type of coil or cylindrical permanent magnet as for a two-frequency laser interferometer.

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Portable Hearing Induction Loop

Induction Loop
Induction Loop

These units are used to broadcast local audio, such as from a public address system or local microphone. They accomplish this by producing a modulated magnetic field that a hearing aid is capable of picking up.

Back Panel
Back Panel

Not many controls on this bit of equipment. A bi-colour LED for status indications, a microphone, external audio input, charging input & a power switch.

Internals
Internals

Popping the cover off reveals a small lead-acid battery, 2.1Ah at 12v. This is used when the loop is unplugged.

Main PCB
Main PCB

Here’s the main PCB, which takes care of the audio & battery charging. The inductive loop itself is just visible as the tape-covered wire bundle around the edge of the casing.

Audio & Power Input
Audio & Power Input

Here’s the input section of the main PCB. The microphone input is handled by a SSM2166 front-end preamplifier from Analog Devices.

Power Amplifier
Power Amplifier

This audio is then fed into a TDA2003 10W Mono Power Amplifier IC, which directly drives the induction coil as if it were a speaker. Any suitable receiving coil & amplifier can then receive the signal & change it back into audio.

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Electronic Lighter – eBay Freebie

With a recent order from a Chinese seller on eBay, this little gadget was included in the package as a freebie:

Electronic Lighter
Electronic Lighter

I’ve not smoked for a long time, so I’m not too sure what use I’m going to find for this device, but it’s an electronic lighter!

Pyromaniac Mode
Pyromaniac Mode

Pushing the slider forward reveals a red-hot heater, mounted in the plastic (!) frame.

Charging Mode
Charging Mode

Pushing the other way reveals a USB port to charge the internal battery.

Core Removed
Core Removed

A couple of screws releases the end cap from the cover & the entire core unit slides out. Like all Chinese toys it’s made of the cheapest plastic imaginable, not such a good thing when heat is involved.

Heating Element
Heating Element

The element itself is a simple coil of Nichrome wire, crimped to a pair of brass terminals. The base the heater & it’s terminals are mounted to is actually ceramic – the surround though that this ceramic pill clips into is just the same cheap plastic. Luckily, the element only remains on for a few seconds on each button push, there’s no way to keep it on & start an in-pocket fire, as far as I can see.

Main PCB
Main PCB

The main PCB clips out of the back of the core frame, the large pair of tinned pads on the left connect to the heater, the control IC has no numbering of any kind, but considering the behaviour of the device it’s most likely a standard eCig control IC.

LiPo Cell
LiPo Cell

The other side of the board has the USB port on the right, the Lithium Polymer cell in the centre, and the power button on the left. The cell itself also has no marking, but I’m guessing a couple hundred mAh from the physical size.

 

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Velleman MK179

Completed Kit
Completed Kit

This is the Velleman MK179 Proximity Card Reader, which is supplied in kit form. In the image above you can see the completed kit, the read coil is etched onto the black PCB on the left. Bringing a recognised card close to the coil operates the relay on the main PCB for a programmable amount of time.

Main PCB
Main PCB

Closeup of the main PCB, 12v DC input at top right. Left IC is an LM358 dual Op-Amp, the IC on the right is a PIC12F629 with Velleman’s custom firmware.
Logic power is supplied to the ICs & the oscillator from the LM7805 regulator at the top of the PCB. The relay is a standard 15A SPDT 12v coil relay, with the switch contacts broken out onto the screw terminals on the left.

Schematic Diagram
Schematic Diagram

As it is not provided with the kit, unlike other Velleman kits, here is the schematic for this.

 

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Camcorder CRT Viewfinder

CRT Assembly
CRT Assembly

Here are the viewfinder electronics from a 1984 Hitachi VHS Movie VM-1200E Camcorder. These small CRT based displays accept composite video as input, plus 5-12v DC for power.

Screen
Screen

Here is the front face of the CRT, diameter is 0.5″.

Power Board
Power Board

Closeup view of the PCB, there are several adjustments & a pair of connectors. Socket in the upper left corner is the power/video input. Pinout is as follows:

  1. Brown – GND
  2. Red – Video Input
  3. Orange – +12v DC
  4. Yellow – Record LED
The potentiometers on the PCB from left:
  1. H. ADJ
  2. V. ADJ
  3. BRIGHT
  4. FOCUS
PCB Part Number reads: EM6-PCB
This unit utilises the BA7125L deflection IC.
Solderside
Solderside
Reverse side of the PCB, very few SMT components on this board.
Tube Assembly
Tube Assembly
Here is an overall view of the CRT assembly with scan coils. Tube model is NEC C1M52P45.
Electron Gun
Electron Gun

Closeup view of the CRT neck, showing the electron gun assembly.

 

CCTV Camera
CCTV Camera

The old CCTV camera used to feed a composite signal to the CRT board. Sanyo VCC-ZM300P.

CCTV Camera Connections
CCTV Camera Connections

Connections at the back of the camera. Red & Black pair of wires lead to 12v power supply, Green & Black pair lead to the CRT board’s power pins. Seperate green wire is pushed into the BNC video connector for the video feed. video ground is provided by the PSU’s ground connection.

Connections
Connections

Finally the connections at the CRT drive board, left to right, +12v, Video, GND.

Screen Operation
Screen Operation

Display taking video signal from the CCTV camera.

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BigBen DSi Inductive Charging Dock

Front
Front

Here is a Inductive charger designed for the Nintendo DSi. Cheap Chinese build, but it does work!

Overview
Overview

Top has been removed from the unit here. Most prominent in the centre is a solid steel bar, simply there to give the device some weight.
Pair of Tri-colour LEDs at the front indicates charging status.
Induction coil is on the left, with the controller & oscillator PCB at the top.

PCB Closeup
PCB Closeup

Closeup of the PCB, ICs have had their markings ground off.

Coil
Coil

Induction coil. This couples power into a coil built into a special battery, supplied with the base, to charge it when the DSi is placed on the dock.

Label
Label

Information Label on the base.

Power Input
Power Input

Standard DSi charger port, connects to the charger you get with the DSi. Power switch is on the right.

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IDE Zip Drive

Top
Top

An old IDE interface Zip drive. This fits in a standard 3.5″ bay.

Cover Removed
Cover Removed

Top cover removed from the drive, IDE & power interfaces at the top, in centre is the eject solenoid assembly & the head assembly. Bottom is the spindle drive motor.

Head Assembly
Head Assembly

Head assembly with the top magnet removed. Voice coil is on the left, with the head preamp IC next to it. Head chips are on the end of the arm inside the parking sleeve on the right. Blue lever is the head lock.

Controller
Controller

Controller PCB removed from the casing.

Spindle Motor
Spindle Motor

Spindle motor. This is a 3-phase DC brushless type motor. Magnetic ring on the top engages with the hub of the Zip disk when insterted into the drive.

Magnets
Magnets

Magnets that interact with the voice coil on the head assembly.

Head Armature
Head Armature

Head armature assembly removed from the drive. The arm is supported by a pair of linear bearings & a stainless steel rod.

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Southwestern Bell Freedom Phone

Phone
Phone

This is an old cordless landline phone, with dead handset batteries.

Handset Radio Board
Handset Radio Board

Here’s the handset with the back removed. Shown is the radio TX/RX board, underneath is the keyboard PCB with the speaker & mic. All the FM radio tuning coils are visible & a LT450GW electromechanical filter.

Handset Radio Board Bottom
Handset Radio Board Bottom

Radio PCB removed from the housing showing the main CPU controlling the unit, a Motorola MC13109FB.

Keypad Board
Keypad Board

The keypad PCB, with also holds the microphone & speaker.

Handset Keypad Board Bottom
Handset Keypad Board Bottom

Bottom of the keypad board, which holds a LSC526534DW 8-Bit µC & a AT93C46R serial EEPROM for phone number storage.

Base Main Board
Base Main Board

Here’s the base unit with it’s top cover removed. Black square object on far right of image is the microphone for intercom use, power supply section is top left, phone interface bottom left, FM radio is centre. Battery snap for power backup is bottom right.

Power Supply Section
Power Supply Section

PSU section of the board on the left here, 9v AC input socket at the bottom, with bridge rectifier diodes & main filter capacitor above. Two green transformers on the right are for audio impedance matching. Another LT450GW filter is visible at the top, part of the base unit FM transceiver.

ICs
ICs

Another 8-bit µC, this time a LSC526535P, paired with another AT93C46 EEPROM. Blue blob is 3.58MHz crystal resonator for the MCU clock. The SEC IC is a KS58015 4-bit binary to DTMF dialer IC. This is controlled by the µC.

Base Main Board Bottom
Base Main Board Bottom

Underside of the base unit Main PCB, showing the matching MC13109FB IC for the radio functions.

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Hair Dryer

Housing
Housing

This is a 1500W hairdryer, death caused by thermal switch failure.

Switch
Switch

This is the switch unit. Attached are two suppression capacitors & a blocking diode. Cold switch is on right.

Heating Element
Heating Element

Heating element unit removed from housing. Coils of Nichrome wire heat the air passing through the dryer. Fan unit is on right.

Thermal Switch
Thermal Switch

Other side of the heating element unit, here can be seen the thermal switch behind the element winding. (Black square object).

Fan Motor
Fan Motor

The fan motor in this dryer is a low voltage DC unit, powered through a resistor formed by part of the heating element to drop the voltage to around 12-24v. Mounted on the back of the motor here is a rectifier assembly. Guide vanes are visible around the motor, to straighten the airflow from the fan blades.

Fan
Fan

5-blade fan forces air through the element at high speed. Designed to rotate at around 13,000RPM.

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Current Cost ‘Envi’ CC128 Power Meter

Display Unit
Display Unit

This is the Current Cost CC128 Real Time Power Meter. Shown here is the display unit, British Gas issued these free to some customers.
This unit measures current power draw in Watts, cost of power currently being used (requires unit price to be set), overall kWh usage over the past 1, 7 or 30 days & power trends during the day, night & evening. Also displays current time & current room temperature.

Display PCB
Display PCB

Here the front panel of the display has been un-clipped. At the bottom are the RJ-45 serial port & power connections.
This unit uses a PIC micro-controller as it’s CPU (PIC18F85J90) Just above & left of the CPU is the 433MHz SPD radio receiver module. The chips on the right of the CPU are a 25LC128 SPI serial EEPROM for data storage & a 74HC4060 14 stage binary counter, to which is connected the 32kHz clock crystal. The red wire around the top of the display is the antenna for the radio receiver.

For more info on the CC128 in general, the serial port & software for computer data logging, see this link
See this link for Current Cost’s list of software

Processor & Radio
Processor & Radio

Closeup of the ICs on the mainboard.

Transmitter Unit
Transmitter Unit

Here we have the transmitter unit, with Current Transformer (CT). The red clamp fits around one of the electric meter tails & read the current going to the various circuits. This unit is powered by 2x D cells, rated at a life of 7 years.

Transmitter PCB
Transmitter PCB

The PCB inside the transmitter. Again very minimal design, unknown controller IC, 433MHz radio transmitter on right hand side with wire antenna. Two barrel connectors on left hand side of board allow connection of up to two more CT clamps for measurement of 3-phase power. Centre of board is unmarked header. (ICSP?)

Current Transformer
Current Transformer

CT unit. Inside is a coil of wire & an iron core which surrounds the cable to be measured.

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Western Digital 160GB 2.5″ HDD

Top Of Drive With Label
Top

This is a Western Digital drive recently removed from my laptop when it died of a severe head crash.
Top of drive can be seen here.

Top Removed From Drive
Top Removed

Here the cover has been removed from the drive, showing the platter, head arm & magnet. Yellow piece top left is head parking ramp.

Head Arm of Drive
Head Arm

The head assembly of the drive is shown here. The head itself is on the left hand end of the arm in the plastic parking ramp. The other end of the arm holds the voice coil part of the head motor, surrounded by the magnet.

Bottom Of Drive with PCB
Bottom Of Drive with PCB

Bottom of drive, with controller PCB. SATA interface socket at bottom.

PCB removed from bottom of drive. Spindle motor connections & connections to the head unit can be seen on the bottom of the drive unit.

Controller PCB. Supports the cache, interface & motor controller ICs.

Closeup of the motor driver IC, this controls the speed of the spindle motor precisely to 5,400RPM. Also controls the voice coil motor controlling the position of the head arm on the platters.

Interface IC closeup. This IC receives signals from the head assembly & processes them for transmission to the SATA bus. Also holds drive firmware, controls the Motor driver IC & all other functions of the drive.

Cache Memory IC.