Electronics wizards; speculatively analyse this circuit board...

A while ago, I bought a box of random surplus stuff and it had a big stack of these circuit boards in it. The only marking on the board is ‘IN CAR 001’, which might give us a clue, but we’ll get back to that…

OK, looking at the track side of the board, it’s clear there are four distinct channels of operation, terminating in a bunch of screw terminals at the top end of the board; immediately facing the larger row of terminals are four sets of what appear to be power transistors or similar; because of their spacing, I can only read the designation on the front ones, which say MTP3055A, anyway, I’d say that must be the output stage…
Immediately below them are four rows of smaller transistors; 2N7000’s; I assume this is some kind of amplification or switching stage.

On the other end of the component side, there are some ICs - HCF4049 (Hex buffer/converter), HCF4024 (Binary ripple counter), GD4093 (some logic gate chip, I think), SI7661 (voltage converter), plus a load of resistors and a few other transistors dotted about.

Now, I’m sure it would be quite possible to trace a complete layout of this circuit and deduce the precise nature of its function that way, but I can’t escape the temptation to work it out by ‘feel’ - the thing looks like a motor controller of some kind, but the inputs (Just power, ground and one signal line) and the outputs (just four pairs of output lines) seem to rule out a stepper motor controller or even a motor speed controller.

My best guess at the moment, based on the layoiut, the inputs/outputs, the kind of components, the four channels and the name ‘In Car 001’ (and In Car Systems’ on some other devices that were in the surplus box) is that we’re looking at an after-market vehicle central locking controller board.

Anyone care to agree/diasagree/speculate?

Holy crap, thems a lot of transistors!

Wow. I’m at a complete loss, but I would speculate that you are pretty close in saying it’s a motor controller of some sort. . . At first, I was going to say some sort of audio amplifier–especially with those trannies towards the bottom with the copper posts on them–but the board doesn’t have any terminals that would resemble something one would see on an audio amplifier.

In any case, I wouldn’t put any money on reading that label on the board. It could be just a part number that we recognize as two words. . . They could be acronyms for something else.

Are you sure it’s not Darth Vader’s chest-mounted control panel?

Dunno; as I said, there were a couple of other items in the box manufactured by a (defunct, I think) company called ‘In Car Systems’ and they consisted of car after-market modifications - one of them was a steering wheel-mounted keypad and IR transmitter for controlling a mobile phone - I actually managed to understand how the IR receiver circuit works and have used it in one of my robotics projects.

But yes, that is a lot of transistors; I think, though, that they are doing more than just amplifying a signal - I haven’t bothered to check, but my impression (again, from the ‘feel’ of the layout) is that they are arranged so that the polarity of the outputs can be fully reversed (to drive a DC motor in either direction, not just turn it on or off)

I want to play but the link doesn’t work.

Nevermind my last…seems ok now.

I’d say its a remote accessory board. Maybe to let you operate the power door locks or power windows or power sunroof remotely. Usually they use relays for this but maybe there’s some special application where relays won’t work. WAG: an RF sensitive environment where point contacts would throw off too much EMI?

A 4093 is a quad 2 input NAND gate.

My guess is that this is part of a car alarm circuit. You’ve got four push-pull (maybe?) outputs driven by only one signal with a bunch of logic gates including a binary ripple counter. I’m trying to think of something that would use some sort of sequencer, and the best thing I can come up with is this is the board that if the alarm is set, it will beep the horn and flash the lights and blinkers.

Either that or it’s for a car remote that when you press the button the first time it unlocks the doors, and if you press the button a second time it locks the doors.

Power it up and give it a signal and see what the outputs do.

That will be somewhere on my list of things to try; I’ve got about a dozen of these boards - it may be that they were in the box because they are junk (although actually, I suspect they are bankrupt inventory), but as far as I can see, there’s nothing much about the board that won’t work at, say, 9 volts, so I reckon I should be able to try testing it with just a battery and some lamps.

I’ll have to look at how the the ripple counter is wired up; it might be that they are just using it to sustain a pulse (i.e. by treating all bar one of the outputs as a single item).