Forrest W Christian wrote:
>I am slowly moving to building automatic test jigs for most of the
> products, so staff (or I) can test them in an automatic fashion.  Most
> of these so far have been built as one-off designs.... but that's
> getting old fast.
>
> I think my job would be a lot easier if I could come up with a piece of
> 'pin reading' circuitry I could easily step and repeat for *lots* of
> pins, that would let me both read the voltage of each pin, plus try to
> drive it to a certain voltage level.   Of course, this needs to be
> relatively indestructable, with voltages up to around 30V on current
> products, and 50-60V on coming ones.   Most of the pins I either need to
> wiremap (I.E. verify connected to another pin on another connector, and
> only that pin), or verify connection to a voltage or ground.   For ones
> with more exotic needs, I can do one-off circuitry to measure the more
> critical waveforms.
>
> The thought I had was a DAC through a current limiting resistor to the
> pin, and another resistor from the pin to an ADC.  That would work for a
> lot of it, but it seems rather crude for some reason.
>
> Has anyone played with some sort of 'universal pindriver' for automatic
> test purposes like I describe?   Does the ADC/DAC pair sound reasonable?

Back in 2006 we built a custom test fixture, which would read voltages on 
power pins, output waveforms and read them back to make sure the pulsewidths 
were within the acceptable range:

http://maksimov.org/piclist/test_fixture/

The fixture ended up being far more complicated than the device under test, 
but the development effort paid off over time because the tester was able to 
identify marginal cases which we couldn't test for using any other means 
(slow transistors, poor loading, etc) and allowed us to move production to 
the Far East. Of course, it would not have been worth the cost if the 
volumes were too low.

I have a hard time envisioning a "generic" tester that could accomplish the 
same task.

When you say "step and repeat", do you mean:

- Step and repeat this circuitry in your schematic editor, or
- Have some kind of multiplexor on the other end of this circuitry that 
would sequentually connect the circuit to the DUT?

Vitaliy 

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist