Roman Black wrote:

>>   PIC
>> -------+
>>        |                                   D.U.T.
>>    RB7 +-----3.3K----+-------> A ------------+
>>        |             |                       |
>>    RB6 +-----330-----+                       |
>>        |                                  | /  e
>>    RB5 +-----3.3K----+-------> B ---------|
>>        |             |                 b  | \  c
>>    RB4 +-----330-----+                       |
>>        |                                     |
>>    RB3 +-----3.3K----+-------> C ------------+
>>        |             |
>>    RB2 +-----330-----+
>>        |
>> -------+
>
>
>Hi Dan, yes I think that is a good start, but you really
>need analogue inputs to make this work well. Also it would
>be nice to have analogue outputs... TI make some quad D-A
>converters at 10 bit and 12 bit, not too expensive.
>

Hi Roman, a full-blown device tester would be nicer, as this
one is a little light on the dynamic testing end of things.

Unfortunately, it appears to be somewhat difficult to be able to
place a 3-pin part willy-nilly into a 3-pin socket and be able to
do perfectly symmetrical measurements on all pins - then you need
a switcher to be able to connect your analog input/etc to each pin
as required, once the pins have been ID'ed - got any ideas of how
to do this easily?

A PIC73 does have 3 A/D channels you could connect to points A/B/C.
Also has 2 PWM channels which could gen analog signals, and then
maybe a 3rd PWM in s.w. Maybe a clever re-assignment of the pins
rather than use portB.
============


>I think I would prefer to have a 15vdc supply, and be able
>to adjust this via the DACs. Then measure the result via
>the ADC inputs. Could use 2x 9v batteries to make it portable.
>

Yeah, 15v would be nice. But now to make everything symmetrical
you need some hi-V pin drivers that can function as both input
and outputs, plus a switching matrix for all the pins. Small
wonder those universal testers cost so much.
================


>Your procedure seems good, to check for obvious diode
>junctions first, then explore the possible variations.
>Testing Vsat well would maybe require a larger current
>source, I like to test stuff at 500mA or 1A etc. I'm not
>sure how this would be handled or even if it is necessary.

What on earth are you testing here that you need to run
500mA thru the junction. Certainly not Vbe[sat] of a BJT.
Maybe Vce[sat]? Rectifier diode?


best regards,
- dan michaels
www.oricomtech.com
========================

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