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Transistor tester

Posted: Thu Mar 15, 2012 12:53 am
by foxmiles
I ran across a design for a neat little tool a couple months ago, it can identify a bunch of discrete components: transistors, mosfets, diodes, etc. It's based on a atmega8, though a 328 works fine once you get the firmware compiled.
Transistor Tester, no component
Transistor tester, LED inserted
Transistor tester, Transistor inserted
The Source: (You probably want to run this through google translate) ... stortester

UPDATED FILE 3/19/2012 - V0.2 - includes Fuse Bits, updated schematic & PCB with groundplane.

Re: Transistor tester

Posted: Fri Mar 16, 2012 7:23 pm
by Jarod
I'm done with chemical etching. I'm not sure if the boards we have are coated with photoresist or something.

I can do toner transfer perfectly. every time its perfect.

But I put the board into the acid and it gets this film over all the copper and sits there and never actually etches properly. I'm not sure if I could get it to come off with some kind of chemical, it wont come off with sandpaper, as I always sand the copper right before I transfer the toner.

I tried doing an isolation route with my dremel... that turned out pretty bad, my hands aren't exactly steady enough to double as a CNC machine, and my CNC machine isn't much better, especially since the z axis refuses to move most of the time.

I think it would work with my hand routed board but I don't have any of the .100nf caps and the .33nf or whatever they are.
So I've decided to wait until the CNC is working better or I figure out whats going on with the pcb material, and I've got all the proper components.

Re: Transistor tester

Posted: Sat Mar 17, 2012 1:30 am
by foxmiles
I'm not sure what would be left behind (it's an acid!). For automotive painting surface prep you always wash with soap and water, sand (or whatever), then go over it with a wax & grease remover. If you don't it can cause problems, usually fish-eyes from silicone contamination(it's in most waxes), various adhesion problems. But that's pretty unrelated, so I really don't know.

Re: Transistor tester

Posted: Mon Mar 19, 2012 7:12 pm
by Jarod
I modified your design to add a ground plane for easier etching with a chemical etchant, I've made some new etchant so I'm going to give it another go and see if something was mixed up wrong last time.

Heres the archive with the ground plane added: (EDIT: OP updated with ground plane and improvements, removed this attachment to avoid confusion)

Re: Transistor tester

Posted: Mon Mar 19, 2012 11:05 pm
by Jarod
Well, It was indeed a problem on my end, after several uses the solution must be "recharged" either by bubbling air through it, or adding more hydrogen peroxide.

I got a (mostly) successful etch earlier today, theres a few traces that got eaten up more than id like but it should work fine.

I've been slowly populating the board, I may have a small issue with the IC socket, one of the pins has disappeared, I think its connected but I'm not sure. I think the only things I need now are all the little caps, the button, and a header to connect the display to, then I can put it in a box or something.

Heres a picture of the bottom of the board. (EDIT: replaced the really blurry picture with a sharper one)

Re: Transistor tester

Posted: Tue Mar 20, 2012 1:49 am
by foxmiles
Looks good, Hope it works. 2 caps are just filter caps for the voltage regulator, you can sub electrolytic or whatever, I don't think they are critical. The other one may be, I basically copied the schematic, so I'm not sure what that's for.
UPDATE: I just looked it up, just another filter cap, it helps stabilize the adc reading. Use whatever you have on hand (preferable a fairly small value, it charges through the adc, and not a i/o pin). You may not need it at all, at least not for initial testing.

I'm looking up the fuse settings

I used:
LOW = 0x62
HIGH = 0xD9
EXT = 0xFF


Good Idea on the ground plane, I thought about it when I was copying the schematic and never thought about it again. I've been cleaning up the schematic a bit, I'll update the whole thing eventually.
A few notes:
1. I put the display on the bottom, if you attach the headers to the top it will hang off the board like mine does, not a big deal. it will be harder to solder on the bottom.
2. I planned to do the top side with jumper wires, so only need single sided board is needed. It's not perfect, but it's good enough for now.

Re: Transistor tester

Posted: Tue Mar 20, 2012 2:29 am
by foxmiles
Replaced original file with latest. My ground plane didn't turn out quite as good as yours, I need to learn a bit more about them I guess.

Re: Transistor tester

Posted: Thu Mar 22, 2012 5:55 pm
by Jarod
Got it working, well mostly anyways.

It detects any capacitor much larger than 10 uF as a N-JFET second line says GDS = 231.

Other than that it seems to work great, detects leds, even multicolor leds.

I've wired a switch to it and everything. I had a royal fit with grounds. the ground plane I put on was rather troublesome. it didn't connect everywhere, probably due to poor etch resist. I had to solder jumper wires from one side of the board to 2 other locations so the display and voltage regulator would be grounded.