Here’s a tiny ethernet switch from the great fle market that is eBay – the Tenda S105. This unit has 5 ports, but only supports 10/100M. Still, for something so small it’s not bad.
Bottom
Not much on the bottom, there’s a pair of screw hooks for mounting this to a surface.
Ports
The 5 ports on the front actually have the pins for the unused pairs of the ethernet cables removed – saving every penny here.
PCB Top
The casing just unclips, revealing the small PCB. Nothing much on the top, just the connectors, isolating transformers & the crystal for the switch IC.
PCB Bottom
The bottom of the PCB is a little more busy, mainly with decoupling components. There’s a 3.3v linear regulator to step down the 5v input for the switch IC.
Switch IC
The IC doing all the data switching is an IP175G 5-Port 10/100 Switch from IC+ Corp. No datasheet available for this, but it’s going to be a bog-standard switch.
Here’s a modern LED bulb, that unfortunately decided to disassemble itself within a few minutes of being installed in a light fitting! The base plastic snapped off the main aluminium body at the screw posts!
Input Rectifier
The PCB in the base holds nothing but the input components. Above is the bridge rectifier.
Fusible Resistor
The other side of the PCB has a 10Ω fusible resistor, for protection.
LED PCB
The LED PCB itself has the driver IC, which is a CYT3000A linear constant current IC, that runs direct from full-wave rectified mains. The single resistor sets the LED current, but there aren’t any smoothing capacitors on the DC rail, so this bulb would flicker a lot.
Here’s another Dyson teardown, in my efforts to understand how marketing have got hold of relatively simple technology & managed to charge extortionate amounts of money for it.
This is the DC35, the model after the introduction of the brushless digital motor.
Back Cap Removed
On this version the mouldings have been changed, and the back cover comes off, after removing the battery retaining screw. It’s attached with some fairly vicious clips, so some force is required. Once the cap is removed, all the electronics are visible. On the left is the motor itself, with it’s control & drive PCB. There’s another PCB on the trigger, with even more electronics. The battery connector is on the right.
Trigger PCB
Here’s the trigger PCB, which appears to deal with DC-DC conversion for powering the brush attachments. The QFN IC with yellow paint on it is an Atmel ATTiny461 8-bit microcontroller. This is probably controlling the DC-DC & might also be doing some battery authentication.
“Digital Motor”
Here’s the motor & it’s board. The windings on the stator are extremely heavy, which makes sense considering it’s rated at 200W. The main control IC is a PIC16F690 from Microchip. Instead of using an off the shelf controller, this no doubt contains software for generating the waveforms that drive the brushless motor. It also appears to communicate with the other PCBs for battery authentication.
Stator
Desoldering the board allows it to be removed from the motor itself. The pair of windings are connected in anti-phase, to create alternating North-South poles depending on polarity. Since the existing controller is unusable due to software authentication with the other parts, I might have a go at building my own driver circuit for this with an Arduino or similar.
Blower Assembly
The blower assembly is simple plastic mouldings, pressed together then solvent welded at the seam.
Impeller
The impeller is just a centrifugal compressor wheel, identical to what’s used in engine turbochargers.
Motor Control Board
The inside face of the control PCB holds the 4 very large MOSFETs, IRFH7932PbF from International Rectifier. These are rated at 30v 20A a piece, and are probably wired in a H-Bridge. There’s a bipolar Hall switch to sense rotor position & rotation speed, and an enormous pair of capacitors on the main power bus.
Motor Control Board Reverse
Not much on the other side of the PCB other than the microcontroller and associated gate drive stuff for the FETs.
Battery Pack Opened
The battery pack is similar to the DC16 in it’s construction, a heavily clipped together plastic casing holding 6 lithium cells. In this one though there’s a full battery management system. The IC on the top of the board above is a quad Op-Amp, probably for measuring cell voltages.
Battery BMS Bottom
The other side of the BMS board is packed with components. I wasn’t able to identify the QFN IC here, as it’s got a custom part number, but it’s most definitely communicating with the main motor MCU via I²C over the two small terminals on the battery connector.
I have yet another receipt printer, this one appears to be brand new. It’s possibly the smallest thermal 80mm printer I have at the moment, and has both USB & Serial interfaces.
Controller PCB
There’s not much to these printers at all. Removing a single screw allows the case halves to separate, showing the guts. The controller is based around a Texas Instruments TMS320VC5509AFixed-Point DSP. It’s associated Flash ROM & RAM are to the right.
Power supply is dealt with in the top right of the PCB, with the interface ports further left.
Print Head
Here’s the thermal mechanism itself, with the large print head. The stepper motor to drive the paper through the printer is just peeking out at top right. The paper present sensor is just under the left hand side of the print head.
On the boat I have installed custom LED lighting almost everywhere, but we still use CFL bulbs in a standing lamp since they have a wide light angle, and brightness for the size.
I bought a couple of 12v CFLs from China, and the first of these has been running for over a year pretty much constantly without issue. However, recently it stopped working altogether.
12v CFL
Here’s the lamp, exactly the same as the 240v mains versions, except for the design of the electronic ballast in the base. As can be seen here, the heat from the ballast has degraded the plastic of the base & it’s cracked. The tube itself is still perfectly fine, there are no dark spots around the ends caused by the electrodes sputtering over time.
Ballast
Here’s the ballast inside the bottom of the lamp, a simple 2-transistor oscillator & transformer. The board has obviously got a bit warm, it’s very discoloured!
Failed Wiring
The failure mode in this case was cooked wiring to the screw base. The insulation is completely crispy!
Direct Supply
On connection direct to a 12v supply, the lamp pops into life again! Current draw at 13.8v is 1.5A, giving a power consumption of 20.7W. Most of this energy is obviously being dissipated as heat in the ballast & the tube itself.
Ballast PCB
Here’s the ballast PCB removed from the case. It’s been getting very warm indeed, and the series capacitor on the left has actually cracked! It’s supposed to be 2.2nF, but it reads a bit high at 3nF. It’s a good thing there are no electrolytics in this unit, as they would have exploded long ago. There’s a choke on the DC input, probably to stop RFI, but it doesn’t have much effect.
Supply Waveform
Here’s the waveform coming from the supply, a pretty crusty sinewave at 71.4kHz. The voltage at the tube is much higher than I expected while running, at 428v.
RFI
Holding the scope probe a good 12″ away from the running bulb produces this trace, which is being emitted as RFI. There’s virtually no filtering or shielding in this bulb so this is inevitable.
Earlier today, one of my neighbours put their dishwasher out for the scrap man. After asking if I could appropriate it in the interest of recycling the Ham Way™, I was told it wasn’t draining. The engineer called out to fix it had claimed it was beyond economical repair.
A quick test showed that indeed the drain pump wasn’t operating correctly – very poor pumping capacity & a horrid grinding noise.
Drain Pump
Here is the drain pump on the bottom of the machine. Strangely for a dishwasher, everything underneath is very clean & free from corrosion.
Pump Rotor
On removing the securing screw & unlatching the pump from it’s bayonet mount, the impeller instantly tried to make a break for freedom – it has come off the splines of the rotor shaft.
In the past I’ve tried to remove these rotors manually – and totally destroyed the pump in the process. They are usually so well secure that replacement is the only option. This particular one must have vibrated off the shaft somehow.
This repair was easy – removing the rotor from the main pump body & gently drifting the impeller back onto the splines.
Repaired Pump
Here the pump is reassembled & ready for reinstallation.
On test the pump sounds normal, & works as expected.
Here’s another active balancing circuit for large ultracapacitor banks, this one is designed for a series string of 6, at 2.5v per capacitor.
Based on the design here, I have transcribed the circuit into Eagle & designed a PCB layout.
Ultracap Balancer Circuit – Click to Embiggen
As can be seen from the circuit diagram above, this is just 6 copies of the circuit from the above link, with screw terminals to attach to the capacitor string.
Ultracap Balancer PCB
And here’s the PCB. the MOSFETs & OpAmps are very small SMT parts, so require a steady hand in soldering. This board can easily be etched by hand as there’s only 3 links on the top side. No need for a double sided PCB.
As always, the Eagle project files & my Eagle library collection are available below:
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
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
As it is not provided with the kit, unlike other Velleman kits, here is the schematic for this.
Here is a Bosch 14.4v Professional cordless drill/driver, recovered from a skip!
It was thrown away due to a gearbox fault, which was easy to rectify.
Internals
Here is the drill with the side cover removed, showing it’s internal parts. The speed controller is below the motor & gearbox here. The unit at the top consists of a 12v DC motor, coupled to a 4-stage epicyclic gearbox unit, from which can be selected 2 different ratios, by way of the lever in the centre of the box. This disables one of the gear stages. There is a torque control clutch at the chuck end of the gearbox, this was faulty when found.
Motor
Here is the drive motor disconnected from the gearbox, having a bayonet fitting on the drive end.
Drive Gear
This is the primary drive gear of the motor, which connects with the gearbox.
Cooling Fan
The motor is cooled by this fan inside next to the commutator, drawing air over the windings.
Gearbox
This is the gearbox partially disassembled, showing the 1st & second stages of the geartrain. The second stage provides the 2 different drive ratios by having the annulus slide over the entire gearset, disabling it entirely, in high gear. The annulus gears are a potential weak point in this gearbox, as they are made from plastic, with all other gears being made of steel.
Charger
Here is the charging unit for the Ni-Cd battery packs supplied with the drill. The only indicator is the LED shown here on the front of the unit, which flashes while charging, & comes on solid when charging is complete. Charge termination is by way of temperature monitoring.
Transformer
Here the bottom of the charger has been removed, showing the internal parts. An 18v transformer supplies power to the charger PCB on the left.
Charger PCB
This is the charger PCB, with a ST Microelectronics controller IC marked 6HKB07501758. I cannot find any information about this chip.
Battery Pack Internals
Here is a battery pack with the top removed, showing the cells.
Temperature Sensor
This is the temperature sensor embedded inside the battery pack that is used by the charger to determine when charging is complete.
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