PSU board – Experimental Engineering

Posted on February 8, 2016 by The Engineer — Leave a comment

De La Rue Coin Counting Machine Followup – PSU Oddness

I did a little more digging into the PSU circuitry of the small coin counting machine, and it’s even more strange than I thought!
The part I originally thought was a transformer on the PSU board is in fact a DC-DC converter module!

Here’s the device after desoldering it from the PCB. It turns out that instead of a transformer, it’s an inductor.

Underneath is the controller electronics, with an COB controller & the switching transistors are under a protective covering of silicone.

Driving this whole lot of PSU randomness is the mains transformer, with a secondary voltage of 35v.

The only reason I can think of that the manufacturer went to this much expense with the power supply is stability – a coin counting machine that miscounts due to power supply surges, sags & spikes wouldn’t be very much use. It’s not likely I’ll see anything similar again, unless I manage to get hold of something like medical grade equipment.

Posted on February 3, 2016February 3, 2016 by The Engineer — Leave a comment

De La Rue Coin Counting Machine

Here’s some teardown photos of an old De La Rue coin counter, used in businesses for rapid counting of change into large bags.

An overview of the whole mechanical system of the counter. Coins are loaded into the drum at the rear of the machine, which sorts them into a row for the rubber belt to pick up & run through the counter. The coin type to be sorted is selected by turning the control knobs on the right.
The control knobs adjust the width & height of the coin channel so only the correct sized coins will be counted.

The counter is driven by a basic AC induction motor, the motor power relay & reversing relay is on this PCB, along with the 5v switching supply for the main CPU board.
The SMPS on this board looks like a standard mains unit, but it’s got one big difference. Under the frame next to the main motor is a relatively large transformer, with a 35v output. This AC is fed into the SMPS section of the PSU board to be converted to 5v DC for the logic.
I’m not sure why it’s been done this way, and have never seen anything similar before.
The edge of the coin channel can be seen here, the black star wheel rotates when a coin passes & registers the count.

Here’s the main controller PCB, IC date codes put the unit to about 1995. The main CPU is a NEC UPD8049HC 8-bit micro, no flash or EEPROM on this old CPU, simply mask ROM. Coin readout is done on the 4 7-segment LED displays. Not much to this counter, it’s both electronically & mechanically simple.

Coin counting is done by the star wheel mentioned above, which drives the interrupter disc on this photo-gate. The solenoid locks the counter shaft to prevent over or under counting when a set number of coins is to be counted.

Under the frame, here on the left is the small induction motor, only 6W, 4-pole. The run cap for the motor is in the centre, and the 35v transformer is just visible behind it.

Main drive to the coin sorting mech is through rubber belts, and bevel gears drive the coin drum.

Posted on September 21, 2015 by The Engineer — Leave a comment

Dell E207WFPc Monitor 12v Conversion

I’m still on my crusade of removing every trace of 240v mains power from my shack, so next up are my computer monitors.

I have 4 Dell monitors, of various models, hooked up to my main PC.

The monitor here is a Dell E207WFPc 20″ widescreen model. There will be more when I manage to get the others apart to do the conversion. However I’m hoping that the PSU boards are mostly the same.

There are no screws holding these monitors together, the front bezel is simply clicked into place in the back casing, these clips are the only thing that holds the relatively heavy glass LCD panel & it’s supporting frame! The image above shows the panel removed. The large board on the left is the power supply & backlight inverter, the smaller one on the right is the interface board to convert the DVI or VGA to LVDS for the LCD panel itself.

Here’s a closeup of the PSU board, the connector at centre right at the top of the PCB is the main power output, and also has a couple of signals to control the backlight inverter section of the PSU, on the left side. The PSU requirements for this monitor are relatively simple, at 14.5v for the backlight & 5v for the logic board.

Here’s the top of the PSU board, very simple with the mains supply on the right side, and the backlight inverter transformers on the left.

Here I’ve hooked into the power rails on the supply, to attach my own 12v regulators. The green wire is +14.5v, and the purple is +5v. Black is common ground.

On doing some testing, the backlight inverter section doesn’t seem to mind voltages between 11.5-14.5v, so a separate regulator isn’t required there. Even running off batteries that’s within the range of both charging & discharging. The only regulator required is a 5v one to reduce the input voltage for the logic PCB.

On applying some 12v power to the regulator input, we have light! Current draw at 12.5v is 2.65A for a power consumption of 33W.

There’s plenty of room in the back casing to mount a 12v input socket, I have left the mains supply intact so it can be used on dual supply.

Here’s the 5v regulator mounted on the back of the casing, all wired up & ready to go.