$20 LCR ESR Transistor checker project

[Per Hansson]

If 500mA supply is tight, I would opt for a more powerful LD1117-V50 linear regulator.

Finally, I would like to know if anyone is interested in my project and if so, where I could share my thoughts and results?

I second madires about the interest in your project, I've looked at building one myself but in the end thought it would be too expensive so a search for a cheaper solution I am all for!
This project really could do with a open source hardware design that is more accessible and cheaper than the current ones are.

That said I just wanted to mention it since you brought up using a LD1117 linear regulator.
It has much worse voltage tolerance than the recommended regulator.
I have quoted an old post from madires below with some more details.
But anyway here is a quick comparsion from the datasheets:

LD1117:
On chip trimming allows the regulator to reach a
very tight output voltage tolerance, within ± 1 % at 25 °C.

Available in ± 1 % (at 25 °C) and 2 % in full
temperature range

MCP1702:
The output voltage tolerance
of the MCP1702 is typically ±0.4% at +25°C and ±3%
maximum over the operating junction temperature
range of -40°C to +125°C. Line regulation is ±0.1%
typical at +25°C.

Some thoughts about selecting a voltage regulator for the Transistor Tester:
- It should handle 100mA (MCU) plus whatever is needed for display and hardware options.
  The MCU does need much less in average but a few checks use high currents very briefly.
- It should be able to handle rapid load changes (sleep mode, normal operation, high current checks, hardware options).
- It should have a good regulation to keep the voltage stable under changing loads.
- It doesn't need to be one with a low output voltage tolerance but such a regulator would improve the tester's accuracy.

We recommend the MCP1702 (250mA, 0.4%, about EUR 0.60). Affordable and much better than a LM78L05 plus TL431.

This brings us to the external voltage reference. The purpose of the reference is to determine Vcc and therefore it should have a tolerance at least one order of magnitude better than the voltage regulator's tolerance. A TL431 is ok for a 78L05, a LM4040 would be better. If you use a MCP1702 you don't need a reference at all unless you're a voltage nut .

I hope this helps with the selection of the voltage regulator and external voltage reference.

[indman]

so a search for a cheaper solution I am all for!

There is no such thing as a good product made from low quality components!
In this project you just need to prioritize. If you want your device to work stable, predictable and long - choose QUALITY components. The DEVKit644 project assumes the use of such QUALITY components as a genuine ATmega644, measuring resistors with 0.1% tolerance, MCP1702 and the possibility of careful tuning and calibration!
If you just want cheaper and something to show on the display - just buy a cheap Chinese clone and don't waste your precious time on empty experiments. 99.9% of users do exactly that and are quite happy with it.

[Per Hansson]

Yes for sure Indman I agree, maybe I should have been more clear: I mean what I wrote in this old post of mine, afaik there is no open source hardware design that fulfills my wishes but I have already 3 different transistor testers so I'm quite good

[Pygmalion]

Here is the optimised circuit with the explanation.

All interested parties are welcome to comment and make further improvements and also to find errors in my thinking and design. If possible, with elaboration.

[proditaki]

I ended up ordering custom PCBs to build a transistor tester

[Pygmalion]

I ended up ordering custom PCBs to build a transistor tester

Where did you get this PCB, and do you have its circuit?

[proditaki]

I ended up ordering custom PCBs to build a transistor tester

Where did you get this PCB, and do you have its circuit?

I got the PCB from PCBway and the project is on github.
https://github.com/vitaliy-bobrov/avr-transistor-tester

[geralds]

Looks very neat. How is it working (accuracy etc)?
Another project on my to-do list...

[Pygmalion]

I guess I'm not the only one who only wants to use only 5V USB supply. And I'm also not the only one who uses the MT3608 just he is using it to boost the voltage before feeding it into the linear regulator. This is necessary in his case because he uses a rechargeable battery.

Well, nice idea!  Had I seen that before, maybe I wouldn't start designing my own.

[Pygmalion]

It would be interesting to make a Transistor Tester project that imitates a typical multimeter: It is powered by two rechargeable NiMH AA batteries.

With two MT3608, one stepping up to 6V and feeding the MCP1702 and one stepping up to 28V for the Zener tester. In this configuration, automatic switch-off is of course a must.

It would also be more energy efficient than a project powered by a 9V battery as the voltage drop of the linear regulator would be far lower. Also, AA battery chargers are much more common than 9V battery chargers.

If I knew how to design a circuit for a latching power switch, I could try it myself, so no. Has anyone tried something like this yet to take a look?

[indman]

Do you have great difficulty finding a 6-9V power supply in your country? 
I am strongly against the use of any kind of boost circuits in this project, even with filter components. If you take this project seriously and not as a toy.
Why raise the voltage first and then lower it again?

[Pygmalion]

Do you have great difficulty finding a 6-9V power supply in your country? 
I am strongly against the use of any kind of boost circuits in this project, even with filter components. If you take this project seriously and not as a toy.
Why raise the voltage first and then lower it again?

I have "finished" my 5V/7-12V powered project in the separate thread. Now I still have a few unanswered questions and a free space on the board for one hardware option. I also hope someone will take another look and find eventual errors.

I don't like batteries, but if I really need them, I prefer AA batteries. I always have a few charged batteries on hand and AA chargers are everywhere. When I was buying my multimeter, 9V or button batteries were an absolute no-go for me. Maybe that's a personal preference, but I can see that modern multimeters are fine with them.

By the way, the project above (https://github.com/vitaliy-bobrov/avr-transistor-tester) uses a Li-ion battery and a booster.

[indman]

By the way, the project above (https://github.com/vitaliy-bobrov/avr-transistor-tester) uses a Li-ion battery and a booster.

That doesn't prove anything. Nowadays there is a wide range of 9V power supplies, there is a Li-ion battery in a compact case, consisting of 2 cells. No voltage increase is required. I'm in favor of this way of feeding this project, no matter how much others convince me in reverse

[Pygmalion]

That doesn't prove anything. Nowadays there is a wide range of 9V power supplies, there is a Li-ion battery in a compact case, consisting of 2 cells. No voltage increase is required. I'm in favor of this way of feeding this project, no matter how much others convince me in reverse

I'm not going to argue about it, because I'm a complete amateur when it comes to electronics, but I do appreciate you making your point.

[madires]

When we worked at the Zener check long time ago we had testers with different boost converters, such as classic MC33063 based and also brand name modules. All were controlled by the test button and powered by the standard 5V regulator. And they all caused issues we had to mitigate by adding delays and adapting the code of the Zener check. Brand name modules cause less issues than an MC33063, for example. The mitigations also work acceptably with the TC-1 clones. The first ones had a crude boost converter creating the voltages for Vcc (followed by a 7805) and the Zener check.

[Pygmalion]

When we worked at the Zener check long time ago we had testers with different boost converters, such as classic MC33063 based and also brand name modules. All were controlled by the test button and powered by the standard 5V regulator. And they all caused issues we had to mitigate by adding delays and adapting the code of the Zener check. Brand name modules cause less issues than an MC33063, for example. The mitigations also work acceptably with the TC-1 clones. The first ones had a crude boost converter creating the voltages for Vcc (followed by a 7805) and the Zener check.

For this reason, to power the device with AA batteries, I suggest that the booster be followed by a linear regulator, but not the 7805, which is really old and not very effective for suppressing the high frequency voltage ripple, but the 1702.

I just found this circuit, which allegedly shows TC-1:


This is exactly the same as Vitaliy Bobrov above did - supplying Li-ion and then smart boost up for both the chip supply and the Zener test at the same time.  Chip supply through a linear regulator which model I cannot recognise, while Zener test supply directly to Zener diode, without even a LC filter.

So how good is TC-1 for normal measurements and for Zener? I didn't understand this part well.

[madires]

So how good is TC-1 for normal measurements and for Zener? I didn't understand this part well.

You can read plenty about the TC-1 and the other variants in this thread, and there are also a few threads dedicated to that clone. It looks nice with the case and LiPo battery, but has many issues. BTW, U4 is an STC15L104W.

[Feliciano]

Short version for Pygmalion (and others): there are many variations of the TC-1 and its derivates. There are several versions of the boost converter too, some with serious design flaws. IMHO, the olders are better. But for sure, it you search a couple of years back on this thread you will find we discussed that part quite a bit.

[Pygmalion]

Short version for Pygmalion (and others): there are many variations of the TC-1 and its derivates. There are several versions of the boost converter too, some with serious design flaws. IMHO, the olders are better. But for sure, it you search a couple of years back on this thread you will find we discussed that part quite a bit.

Yes, I found several threads about the problems and repairs of the TC-1, but I had a hard time finding anything about the design of the power section and how it affects the accuracy of the measurements. This is what I need to understand in order to assess whether it makes sense to power the device with two AA batteries via an MT3608 booster followed by an MCP1702 linear regulator. I see that many devices powered by either a LiIon/LiPo battery or 5V use this logic (admittedly with different boosters and linear regulators), but can't find any hard data on the effects.

[indman]

Yes, I found several threads about the problems and repairs of the TC-1, but I had a hard time finding anything about the design of the power section and how it affects the accuracy of the measurements.

It's just that none of the users are bothered by the same problems as you are. They just use these clones and they're fine with it.

[Feliciano]

Yes, for a precision equipment, we should look for something on the $100+ price range. For around $20, most people would be OK with being able to simply assess whether a particular DUT is damaged or not, or perhaps within the operational window. In that regard, I think madires and previous people have made a remarkable job, with some help from other collaborators of this thread.

If you want to move this a little bit forward, the issue is to achieve voltage stability with load surges, and minimal noise (not only for DC/DC converters but also for linear regulators in this scenario). Another thing would it be to use good quality components, and not the typical knockoffs.

[Yuriy_K]

madires
I understand that not everything can be corrected, but is it possible to correct such measurements.
The lower readings are correct.

[madires]

Noted. I'll look into that.

[porter]

Hi,

I don't know if it's right thread, but anyway to the point... I bought lately GM328A tester from aliexpress, for something like ten bucks with shipping. It came of course with the old version 1.12k of firmware, so i wanted to upgrade it with 1.42m. It had a strange lcd module, with additional unknown chip between buffer and controller, white silicone around the controller, module was mounted on pins on the left side (not on screws). On picture "LCD modules.jpg", on left side is my lcd module from the DIY GM328 red kit.

It turned out that after flashing atmega, this lcd just doesn't work, no matter what, but both lcd modules, this one and one from GM328 "red kit" worked on version 1.13k. I spent almost a week to get this thing working, and here is what i've finally done:

1) no image, garbage on the screen -  generally this module behaves like ST7735, but needs CS switching between sending bytes  in LCD_Data2 (High, Low), like it is in k-versions, after adding it both modules work on 1.42m.

2) this lcd module works in BGR mode, but doesn't react on command 0x36 (and most of the other control commands), so colors have to be inverted by the software, i've added inverted BGR colors to colors.h and defined LCD_BGR_SOFTWARE.

I attach changed files with fixes for the next version.

Thank you for developing this soft!

I have the same tester that you show in your post. Following the notes here and in the Clones file for version 1.55m,
I was able to update the firmware on my tester (after much mucking about  ).
Cheers 
(I haven't tested all functions, but it looks good so far.)

[siealex]

Can any of existing transistor testers explicitly detect Darlington transistors?