Transistor tester schematic IC

Borber said:

I bought that issue. The article describes as title says transistor identifier. It can determine type of transistor PNP, NPN, NJFET, PJFET, NMOS and PMOS. IT allso indicates transistor pins EBC SGD and measures HFE, RDSON and cutoff voltage at fets. Instrument is build arround PIC16F872 it has 2x16 LCD. As I understand instrument is suitable to indicate type of transistor which has no label more than to perform more advanced measurements.

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wizpic said:

hi all
would it be possible for some one to translate this from french to eniglish . now i know most of you would say why need it you got pcb and schematic but i like to read to understand how it works so i would be greatfull is some one could translate it
i have tried but i dont understand 1 bit of french and most of the words come out unreadable

cheers

wizpic

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MikeOhio said:

Well, the uploaded article did the trick. I had to order the PIC and ICs, which arrived today, and I got the tester built this evening. Like WizPic, I have problems with the French but a trip to Google's translation page and a lot of typing (and numerous typos) got me most of the information that I needed. So, here's an update on what I have found to this point.

First, I programmed and tried the 16X1 version. It displays the transistor type and pin-out but cuts off the last letter on the pin-out (but that may be related to the display that I am using). For example, it should display E-B-C (or whatever combination it detects for the leads). What it displays is E-B-. This in itself isn't a problem since it identifies two leads, the one not displayed is, in this case, logically the collector. It does not display the beta value.

I then programmed the 16X2 version and everything displayed as it should.

Getting started was a trial and error process (between what I could translate from the article and just playing with the tester on the bench). There is a jumper on the board marked ST1. The first time you start the tester, this jumper must be in place. The tester will display the verison number and then CALIBRATION will appear on the LCD. This calibration is for FET measurements, if my translation was correct. I'm not sure exactly how this calibration process is supposed to function but removing the jumper will blank the screen and then replacing it and removing it several times finally displays RES G-M and an ohmic value (Gate to Source resistance), then G-D and an ohmic value (Gate to Drain resistance), and finally M-D and an ohmic value (Source to Drain resistance). These values, I assume, are stored in memory since you only have to go through this process initially. At this point the jumper can be removed. On my board, I soldered two pins in place and am using a jumper between the two pins and just leave the jumper on one post when the calibration is completed. The tester will then display *-*-* on the LCD and you are ready to check your transistor.

Shortcomings:
1) The tester will not test germanium or darlington transistors, only silicon, mosfet and jfet.
2) It will not identify a transistor with an internal short. When I shorted out base to emitter, based to collector, and emitter to collector of an NPN transistor, the unit indicated that it was either a P-channel or N-channel JFET, depending on which pins were shorted. So, you can not necessarily rely on the tester alone to identify the type of an unmarked or unknown transistor. Of course, if it identifies an unknown transistor as a JFET, you can always use an ohm meter to check the transistor for an internal short - no short, it is a JFET or, if it shows a short, throw it away because you can't use it anyway!
3) Like other PIC based transistor testers, it can identify the gate of a JFET but not the drain or source.

It's not a bad project and I don't want to discourage anyone, but I think its inability to identify a shorted transistor limits its value as a "tester".

I'm looking forward to comments from those that also build this tester (and I'm going to keep looking for another version!) Thanks to all that have contributed to this topic and I hope what I've noted is of some value to others.

Mike

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