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Two 7-Segment LED's counting pulses.

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New Member
Hi guys. I am new here, and have experience in electronics, but not circuitry.

Here is the scenario. The transmission control unit on my car sends 12v pulses to a diagnostics pin. You get 2 digit trouble codes by hooking up an led to the pin and to ground. You count long led pulses to get 1x, 2x, etc. The short pulses follow to get x1, x2, etc. For example, it will give 5 long pulses with half a second in between, wait a second or so, then give 4 short pulses with a half second in between. This equivalates to a data trouble code of 54.

Instead of hooking up an LED to the pin, can I hook up two 7 segment led's with a proper driver? If so, how would I go about doing this? I am guessing I will need an input latch to lock the first segment led after the long pulses, then activate the second segment led to count the short pulses.

Any feedback would be appreciated. I tried searching around and couldn't quite find exactly what I was looking for.

Thanks. Mike.

Edit: Parts I was thinking of so far

500 ohm resistors
HCF40110 counter/decoder/latch/driver
radioshack 7 segment led's
button to reset

I think my big question is how do I make it switch from one driver to the next after the long pulses are done, and the small ones are about to start?
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New Member
It'll be easier to get a code reader at an auto parts store... but if you want to build something, I'd use a microcontroller. So much easier, at least if you know how to program them. ;)


New Member
I'll take a look into the microcontrollers. I could just buy one, but I want to market them since there isn't anything out there to read the codes. The way these cars are wired, the typical scanners only read a few of the major codes, not all of them.

Thanks for the replies though.
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