PIC - based Germanium Transistor Tester?

[polaris26]

I had an idea for a project that would involve a microprocessor ( PIC maybe?) that could be used
to determine the real Hfe of Germanium transistors.  In practice, you have to take one reading for leakage and then another reading with a given amount
of base current, and then subtract the two.  This also changes rapidly with temperature.  This works ok when you have one or two devices to test, but I
have amassed a collection of various transistors and I don't look forward to testing them all 'by hand'.

I was thinking the readout could display Leakage, Ambient Temperature, and Hfe.
I unfortunately am not very good at programming (just never was my thing) but I'm sure such a project would not be too hard for someone already well-versed in
PIC programming.  If anyone would be interested, I would be happy to lend whatever resources I can to such a project.

Dave

[The Tone God]

I already have built a uC Ge tester but the problem with the temperature idea is knowing how much the temperature is affecting things to offset the output. I wouldn't bother with that instead the user should just to be aware of the issue.

Andrew

[polaris26]

Hi Andrew - I was suggesting just to have a temp sensor read by the PIC and shown in degrees F or C so that if you wanted to record the results of a test or be more
consistant, you could record what the ambient temp was when you tested the device.  I realize you could just use an external thermometer but I thought this would be
more convenient and consistent.  I would be interested to know more about your tester project - is it something a PIC newbie could reproduce (I'd be willing to buy a programmer
or whatever I needed).

thanks,
Dave

I already have built a uC Ge tester but the problem with the temperature idea is knowing how much the temperature is affecting things to offset the output. I wouldn't bother with that instead the user should just to be aware of the issue.

Andrew

[oskar]

Simply having a temperature output from one of these IC thermometers is simple and if you let the whole setup sit still for enough time so you know everything is having the same temperature then you can trust your measurement to be correct. Just make sure the transistor and the thermometer are close and share as much copper as possible and that you give them time enough to settle ( we're talking minutes here, but I really don't do germanium transistors... )

I like heat and measuring it. I've worked with scientific equipment for heat measurement which had lots of those one-chip termometers ( I believe it was the dallas semiconductor ones...) with a digital output. For the equipment to work at a good level they had to know the temperature at various points on the circuit board to cancel out ambient temperature "noise". Measuring heat can easily take off into a nightmare of complexity... trust me on this one!   

Another way to go about it is to give the transistors the same known temperature. Dip the top of them in icewater...

...knowing how much the temperature is affecting things to offset the output

Ah, yes! And this is where the complexity starts to take off... But still we're talking a limited temperature range... the real unlinearity stuff start to get to work once the transistor is getting warm and I dont know if you need to let it get warm to measure it? Because then you would have a real problem. With a constant current and the transistors given a temperature reference ( ice bath ) you could get the setup ready for measures in just 10 minutes...       -yikes!

The idea of measuring temperature is really good thinking but in reality I don't think it would do you no good... It's just to many variables involved.
Don't go there...   

Just getting a temperature reading is easy!
It will probably do you no good!
Just finding out if it is doing you good will be a quest into a jungle with lurking dangers and no map...

[The Tone God]

My tester was pretty simple. Couple of MOSFETs working as switches to take the two readings then the uC spits out the numbers based on the the two A/D readings. I used a regulated DC input instead of a battery so I know the voltage is consistent and the readings will be correct. So I plug it in, stick the transistor into the socket, hit the button and I get a reading of the gain and leakage.

Andrew