The Lazy Man's Germanium Tester

[BetterOffShred]

This project is rad, do you think an ATTiny85 could do this?

That was the first one I had considered as an alternative. The ADC is 10 bit as well. I'd imagine if you have a stable 5 volts supply voltage it would be just as good if not better than the AIO arduinos with dodgy 5 volt references. I think I might have one or two kicking around I could try!

Could always use an external ADC. I was just looking at the MAX1241. A little pricey though perhaps worth the accuracy if you're looking for precision here.

This is my Lazy Man's Germanium tester:

https://www.amazon.com/Pocketable-Multifunctional-Backlight-Transistor-Capacitor/dp/B07X5YS1JN/ref=asc_df_B07X5YS1JN/?tag=hyprod-20&linkCode=df0&hvadid=416638923984&hvpos=&hvnetw=g&hvrand=4105942515975511802&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9005070&hvtargid=pla-845729973092&psc=1&tag=&ref=&adgrpid=93604202533&hvpone=&hvptwo=&hvadid=416638923984&hvpos=&hvnetw=g&hvrand=4105942515975511802&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9005070&hvtargid=pla-845729973092

I've thought about grabbing one of those before. Does it display leakage as well? Has it been tested against other methods? Just curious.

I got a couple little attiny85 dev boards for a weather station I was fooling with, they have built in 5V regulators and a mini usb port for flashing them.

https://www.ebay.com/itm/Digispark-Kickstarter-ATTINY85-Micro-USB-Development-Board-for-Arduino-US-Stock-/191867257317?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l49286&mkrid=711-127632-2357-0

I don't know much about programming them yet

[Phend]

And this thing ? $12.69 on Amazon.
(I do not promote this product)

[Kevin Mitchell]

While I could get the ATTINY85 to function for this purpose, as I played with it I had learned how non-linear the ADC behaves which is not ideal. But for basic purposes and for the transistor tester it works OK - depending on what grade of precision you're looking for.

Just pulled the trigger on a ADS1115 module from Adafruit (preassembled ADC circuit for these kinds of projects). It's 16bit so it'll scale 0.076mv per bit at 5 volts while the arduino's 10bit ADC could only do about 4mv per bit. Also snagged that TS12A4514P (SPST, N/O analog switch IC) - datasheet says logic control input is 2.6v so I could omit the buffer. Otherwise I would have replaced the 4049 with a simple opamp comparator to save breadboard real-estate.
So an update is coming soon 

[Kevin Mitchell]

I don't know much about programming them yet

I use Arduino as ISP to burn bootloaders & program ATTINY or other Atmega chips that I use for proprietary projects.

[BetterOffShred]

And this thing ? $12.69 on Amazon.
(I do not promote this product)

These did not measure leakage from my testing and always are way off from my Atlas DC55

[Vorskla]

Nice project Kevin. I did something similar myself with just a plain ATMega328P as the brains and an MCP4822 (12-bit ADC). I think I also have a unity-gain rail to rail op amp before the ADC powered by 5V, but it's been awhile since I looked at it. The whole thing is built into a 1590B with a transistor socket on top.

Since it doesn't really need to be a speedy process, my code is averaging a whole bunch of ADC measurements. It's probably overkill given the fluctuations GE transistors can have with temperature, but I don't see any harm in it either.

With regards to the other transistor testers people have linked, I'd be wary of those even if they do account for leakage. They often use very different test conditions than the RG Keen circuit (and often don't tell you what those conditions are). The RG Keen circuit tests at ~4uA base current if I remember correctly. I would guess that most generic transistor testers use a current that's quite a bit larger. Both readings would probably be "correct", but they can vary substantially. It depends on the transistor too. I have a DCA75 which is a great device, but its basic HFE measurement can be quite different from what you'd get using RG Keen's circuit - usually displaying a much higher HFE.

[Kevin Mitchell]

Nice project Kevin. I did something similar myself with just a plain ATMega328P as the brains and an MCP4822 (12-bit ADC). I think I also have a unity-gain rail to rail op amp before the ADC powered by 5V, but it's been awhile since I looked at it. The whole thing is built into a 1590B with a transistor socket on top.

Without looking into it, I'm pretty sure the MCP4822 is a dual channel DAC - you pretty much just described my first CV controller design for modular synths - but it had an offset/multiplier post-DAC to scale for a 5 octave range.

Thanks for sharing your experience between the RG circuit and your DCA75. It's a given that the readings would vary as the test parameters aren't the same. As far as I understand, the RG circuit is ideal for Fuzz circuits while typical meters just give you some vanilla specs for general purpose. There's more to the story as I've found on the forum over the years and with recent searches. I feel RG is exhausted talking about it and probably gave a big eye roll to this thread

Edit:
Your first post! Welcome to our DIY haven!

[Phend]

Seems to be boiling down to trust yours ears and not the quality control instruments.
Build a reference fuzz circuit, socket the transistors,  and listen?

[Kevin Mitchell]

Seems to be boiling down to trust yours ears and not the quality control instruments.
Build a reference fuzz circuit, socket the transistors,  and listen?

Consistency, my friend.
If one supplies a fuzz pedal build kit with parts and does not want to disappoint (especially if an audio demo had been provided) it would be ideal to provide devices that have at least been spec'd and are close to the ones in the demo. Or if one is trying to replicate a certain signature fuzz pedal this would be an ideal tool to quickly sort through a lot of them for best matches.

Also, DIY tools for the bench are fun!

[Vorskla]

Without looking into it, I'm pretty sure the MCP4822 is a dual channel DAC

Whoops! Thanks for the correction - I think it's probably an MCP3202. I use both series a decent amount and get them mixed up.

The RG circuit is definitely closer to the kind of currents fuzz circuits will typically see compared to a lot of generic testers out there and also compared to the test conditions used for the numbers in most (if not all) transistor datasheets. A test circuit like his or Kevin's has been a major time-saver for me. I do think it's worth giving an audio test to any set of GE transistors before building or at least socketing them, but using a tester beforehand can definitely weed out suboptimal ones and give you an idea of what values you personally like for which stage.

And yes, DIY tools are fun and I find the whole testing process kind of fun too in a weird way.

[mateusborges]

What you really need is one of these. I doubt anybody will build it. Not enuff sexy mojo.

This looks too sexy hehe

BTW, when reading leakage wich one is the one that matters?

And about geofx gizmo and the TC-1 comparison, if you leave the transistor for 10 min seating quiet before reading the tests they are really close, at least in the ones I´ve tested so far.

[theehman]

Any updates on the simplified version??

[Kevin Mitchell]

Any updates on the simplified version??

It really doesn't get much more simple after the initial post. You could replace the switching IC (CD4016 or CD4066) with a TS12A4514P. In doing so you'd be able to drop the buffer since the TS12A4514P can be triggered at a low threshold from the pulses provided by the Arduino directly.

To further simplify it you could drop the LCD display and use the Arduino IDE's serial monitor to relay the measurements - though it continuously scrolls.

I'll try to update the thread tonight with the latest design on the breadboard. New display, smaller switching IC, no buffer and using a nano instead of a mega 

[Ben N]

Forgive me for what may be a dumb question, but does it do NPN as well?

[Kevin Mitchell]

Ahh didn't have time last night to draw a schematic. I have to clean up the code before I share though it's working wonderfully! Will do an A/B sample of the manual method VS my lazy man design to prove accuracy.

I might also draw up a PCB for a finalized version with all ICs + microcontroller on one board. I'd try to keep it DIY friendly but through-hole 16 bit DACs are pricey - may stick with the ADS1115 module.

Anyways, I'll try to update the thread with the accurate modular/breakout design over the weekend. Probably in an instructables style - it's a mess drawing schematics for modules.

Forgive me for what may be a dumb question, but does it do NPN as well?

Not as is, no. It would have to be modified to measure difference rather than the single point against ground. You'd also have to swap the power supply on the emitter & resistors. I'll further elaborate and add it to the final design!

[theehman]

Any updates on this??

[Kevin Mitchell]

Any updates on this??

There certainly are some updates, just been busy with other things. I'll see if I have time over the weekend to dig into it again. Without getting into great detail right now, the design had taken a few turns as I tried to further simplify things while also using what I consider to be common parts in effort to ditch the breakout module. But that's moving further from being a Lazy Man's work 

I'll be back with what I'll call the most simple design using the 10-bit ADC that most of these MCU's have. We'll call that Version 1.0, expanding from the proto in my first post. That way we can stick a fork in it as the finalized Lazy Man's Germanium Tester.

If anyone has thoughts on this feel free to put them up!

[Kevin Mitchell]

A little update.
I'm drawing a layout for an ATtiny85 version that uses 8 (4x2) segment displays. This is in effort to minimalize the design while using common parts & no breakout modules although you'll need means of an ISP programmer to burn the bootloader & firmware.

Update with breadboard proto & layout preview coming soon. I've got a few things on my bench right now but hope to get this situated during the week so I can get some boards fabricated.

To do;
-Implement a PNP/NPN switch
-Write a lookup table to easily write to 8 single-digit displays using shift registers
-Verify on breadboard
-Design PCB
-Circle back here to introduce the LMGT v1.0

[theehman]

A little update.
I'm drawing a layout for an ATtiny85 version that uses 8 (4x2) segment displays. This is in effort to minimalize the design while using common parts & no breakout modules although you'll need means of an ISP programmer to burn the bootloader & firmware.

Update with breadboard proto & layout preview coming soon. I've got a few things on my bench right now but hope to get this situated during the week so I can get some boards fabricated.

To do;
-Implement a PNP/NPN switch
-Write a lookup table to easily write to 8 single-digit displays using shift registers
-Verify on breadboard
-Design PCB
-Circle back here to introduce the LMGT v1.0

Awesome!!

[Kevin Mitchell]

I think I have the PNP/NPN switching down. Sadly other than a DPDT switch this method also requires a bipolar supply as well as an inverting circuit and a buffer for good measure.


I could swing it a few different ways but the main implication is that the ADC's reading expects a positive voltage in respect to 0v ground. I'll sit on it for a bit but at the moment I can't think of a more efficient way to integrate both polarities within the same circuit.

Definitely open to suggestions.