Author Topic: Multi pin resistance / continuity  (Read 63 times)

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Offline horle

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  • Country: de
Multi pin resistance / continuity
« on: Today at 03:01:19 AM »
Hey guys!

I'd like to check if any of 24 pins in a connector  are shorted. I thought of implementing some switch matrix to route any pin combination to 2 wires and then measure resistance.

I can think of several ways to attack this problem but I'm not sure if any of them might be superior.

Surely I can solve this with a lot of relays, maybe even transistors? I also know there are switch matrix ICs but I'm not sure if I can measure resistances through such a device properly.

So maybe you guys think: poor electronics noob, everyone knows that you use the famous XY to solve this. :)

Any advice that would spare me costly failures are highly appreciated. My hobby budget is quite limited at the moment

Online duak

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  • Country: ca
Re: Multi pin resistance / continuity
« Reply #1 on: Today at 05:15:30 AM »
I had to do a similar test with about 1000 lines on a complex flex circuit.  I used some FPGAs (Field Programmable Logic Arrays) that implemented a 1000 stage shift register.  The shift register implemented a rotating bit (1 on, 999 off) that started at one end and stepped bit by bit to the other end.  Each shift register stage drove an FPGA I/O pin that could be set to provide a weak pull up to Vdd.  Each pin could read or sense the actual output signal and logically compare it to the orginal rotating bit pattern.  If there was an difference, the controller would stop and then determine if there was a short circuit to circuit common or to another output by examining the states of the I/O pins.  This scheme didn't determine actual resistance as the faults essentially short circuits.

I didn't have access to the both ends of the flex but in your case you could implement a checker that drives one end of the cable and reads the other.  In the simplest case the receiver could be 24 LEDs and the driver a hardwired shift register, a rotary switch or even some test points that could be scanned manually.  Note that this scheme requires that the driver provide a connection to either a test voltage or circuit common.

Hope this makes sense,



Offline Brutte

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  • Posts: 476
Re: Multi pin resistance / continuity
« Reply #2 on: Today at 07:21:35 AM »
I had similar problem for bed-of-nails tester.
I have used an eval uC with USB interface, 64 pins used. Each pin could be driven in one of four states:
- output high
- pullup
- pulldown
- output low

32 IOs total.

So essentially through USB I was:
- sending some IO drive sequence,
- 1ms delay
- sensing IO pins.
All that mess of bits was controlled and analyzed by host application.

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