$20 LCR ESR Transistor checker project

[Vitaly_Ne]

Hello everybody.
It was necessary to measure the capacitance of the coaxial wire (about 1m), I plan to make a probe for the oscilloscope, but I noticed something odd.
Compared with the device RM219.
Those. ordinary capacitances measure +/- the same way (taking into account the error), in the photo just for example the capacitance is 1 microfarad (yellow) and 10nF (green) ...
But that's it when measuring a piece of cable - the readings differ twice!??? I measured other pieces 50cm ... and 1.5m ... also a huge discrepancy ...
Moreover, measurements of other components are normal ... if there are discrepancies, then they fit perfectly into the errors (and my needs).
Usually I measure something with either a device or a tester and there have never been any problems ... but here an incomprehensible situation arose with the measurement of the cable .. Maybe someone came across? Is it in different ways or features of measuring instruments?
I want to know what to believe anyway...
Or maybe someone will also conduct a similar test (wire range from 0.75 - 1.2m coaxial), will you have discrepancies?

It’s just that later I’ll calculate the compensation capacity and I don’t know what evidence to build on ...
The cable is marked RG58A / U (but I doubt that this is the original ...)

Tester G328A(BGR), firmware costs 1.13k (from Yuriy_K from page 277)
In principle, I can try to flash 1.44m (Thanks to indman,
  for help in compiling in due time ...), only the USBASP-programmer threw it somewhere, but I can search(But I don't think it's a firmware issue...) ...

p.s. According to the videos on the network, who made such probes, the capacitance is within 30-45nF for people ... i.e. the readings of the tester in this case are greatly overestimated (I don’t understand the reason), but the readings of the device 219 are, as it were, normal ...
This is probably some kind of feature of measurements by a tester of coaxial cables?

[madires]

The Transistor Tester doesn't use an AC signal to measure capacitance. Instead it charges the DUT to a specific voltage, counts the time, and calculates the capacitance from that. It measures the DC capacitance. For a transmission line, e.g. a coax cable, a proper LCR meter with an AC signal is recommended.

[Yuriy_K]

This is probably some kind of feature of measurements by a tester of coaxial cables?

The indications should not depend on the methods of measurement. Here are examples of measurements on different instruments...

Attention! Added,  for the TTester on both firmware, there is a dependence of the readings on the connection of the leads to the measuring terminals.

[Feliciano]

I measured other pieces 50cm ... and 1.5m ... also a huge discrepancy ...

The capacitance of a coax cable is function of its length (think about the capacitance of two conductors in parallel of variable lenght separated a constant distance by a dielectric, the more the length, the more charge can be stored). In fact, if you look at the manufacturer datasheet it will tell you the typical pF/m or nF/m.

[Vitaly_Ne]

The Transistor Tester doesn't use an AC signal to measure capacitance. Instead it charges the DUT to a specific voltage, counts the time, and calculates the capacitance from that. It measures the DC capacitance. For a transmission line, e.g. a coax cable, a proper LCR meter with an AC signal is recommended.

Yes, that's understandable. Unfortunately, I do not have such devices yet. I thought to measure, not perfectly accurately, but at least to decide on further calculations ...
But such a nuance turned out ...

[Vitaly_Ne]

The capacitance of a coax cable is function of its length....

What depends on the length, I know that.
According to the datasheet, the manufacturer claims 85pf per meter.
When I measure a long piece and a short ratio with a tester, this is how it turns out.
Also, if I measure with a multimeter, the length ratio is the same (+/- error) ...
But Yuri wrote that the readings should be the same, but for some reason I have different ones .. moreover, they simply measure the capacitors EQUALLY ... and resistors, etc.
But it was with the cable that such a nuance arose ...
I myself wonder what my problems are ... is it a multimeter? those. According to Yuri's screenshots, his tester readings approximately coincide with mine (70-80pF)

[Vitaly_Ne]

The indications should not depend on the methods of measurement. Here are examples of measurements on different instruments...

Here you have "ideal" ... The tester calibrated ... Everything shows correctly ...
It happens that you need to believe his testimony (they are closer to the datasheet) .. but the multimeter turns out to be a failure for me ...
But why exactly when measuring the cable This is incomprehensible to me ... after all, all other measurements for them practically coincide ...

[oitar]

Any suggestions regarding resetting the fuses would be welcome

Another method for recovering a bricked AVR is using an external clock/oscillator. I did a quick search and found these:

https://www.eevblog.com/forum/beginners/bricked-atmega-1284-with-avrdude!-can-it-be-saved/
https://www.avrfreaks.net/s/topic/a5C3l000000UMBiEAO/t099084
https://www.avrfreaks.net/s/topic/a5C3l000000UboeEAC/t159156
https://classbproject.com/fixes-and-hacks/recovering-a-bricked-avr/

Connected it to an external 1 Mhz source(arduino), the mega324PA even has 125.0 kHz coming out of its PB1 pin. Running avrdudess with -b 1200 -B 56 (16 kHz SCK). Still unable to read signature, or change fuses.

[hojnikb]

• We already had a short discussion about DurandA approach. You can go back to the posts of July 23, 2022 of this thread
• Unless the vendor shows an internal photo (and even in that case we cannot be 100% certain), you cannot know for sure what you're going to get untill you have it in your hands. For instance, last July I bought one T1 and one T7 from Amazon, for $20+ each, from different sellers. One was the real ATmega, the other was a 32pin clone

Guess i'll have to roll the dice and see what i get. It's cheap though, so it won't matter that much.

Just got mine after 3 weeks. It has an unmarked microcontroller. By the looks of it, it seems like a 32pin deal



Is there a way to know which of the clones this is ?

[Obelix2007]

Yes, that's understandable. Unfortunately, I do not have such devices yet. I thought to measure, not perfectly accurately, but at least to decide on further calculations ...

... the ComponentTester is better than you think, correct calibration is important ...

... I carried out the measurement with different devices and documented the results in photos.

Greeting Horst

[Fuzzy Star]

This is probably some kind of feature of measurements by a tester of coaxial cables?

Your photo says: "Measurements of just capacitances are more or less the same ... but when measuring a cable such a spread"
The capacitances you use to compare are 1uF and 10nF. But the capacitance of the cable you're trying to measure is less than 100pF. It's such a low value to say 'spread'. Results are 40pF and 70pF, it's only 30pF difference. With such a low value, your probe capacitances and the connection methods affect the results.
How many pF the Tester shows when there is nothing connected to the probes? (keep the probes connected to the ZIF socket)

Use a 50-100pF capacitor to compare your DMM and Tester. Probably you will see a similar 'spread'.

[Vitaly_Ne]

... the ComponentTester is better than you think, correct calibration is important ...
... I carried out the measurement with different devices and documented the results in photos.

Of course, the tester is an excellent device. Calibrated, I think, is also correct (I have been using it for a relatively long time and figured it out a little) ...
Here you are in the photo, I also look at the instrument readings more or less the same ...
So I have problems with the multimeter ... because. my readings are 70nF closer to those measured by Yuriy_K and you...
___________________
p.s.  I just measured a piece of double-sided textolite and ....
in general I have a COMPLETE misunderstanding ((((
The readings are almost the same (I leaned the contacts several times) +/- a few units of difference ..

[Yuriy_K]

....
in general I have a COMPLETE misunderstanding

Don't you understand that it is impossible to compare the readings of devices with autonomous power and kicking from a mains power supply?
The sensitivity of the TTester is so high that it reacts to the close presence of hands, like an antenna to influence network interference.
In all my examples, there is no mains power and there are no hand pickups.

[Vitaly_Ne]

...With such a low value, your probe capacitances and the connection methods affect the results.
How many pF the Tester shows when there is nothing connected to the probes? (keep the probes connected to the ZIF socket)

Use a 50-100pF capacitor to compare your DMM and Tester. Probably you will see a similar 'spread'.

1. The tester shows 0.05pF-0.1pF
2. measured 15nF almost the same (I think the error is normal) ..
3. I connected the cable to the ZIF - 69-75pF, which is almost similar to the measurements from others ... i.e. tester can be trusted...
then the problem is in the multimeter ... it probably can't cope ...
Okay, I'll focus on the tester.
Thanks to EVERYONE who helped

[indman]

tester can be trusted...
then the problem is in the multimeter ... it probably can't cope ...

The problem is in your multimeter, which has a large error when measuring the picofarad range. Try to measure the usual capacitance of 10-20pF on this multimeter and you will immediately see the difference in the readings.

[Vitaly_Ne]

....Don't you understand that it is impossible to compare the readings of devices with autonomous power and kicking from a mains power supply?
The sensitivity of the TTester is so high that it reacts to the close presence of hands, like an antenna to influence network interference.
In all my examples, there is no mains power and there are no hand pickups.

So I have both a multimeter and a tester powered by batteries ...
I take into account the influence of the hands, and I understand that they can influence ... but the fact is that when everything is connected and the hands are removed - for some reason, when measuring the cable, this is what happens ...
In all other measurements, the tester and multimeter are almost the same ...
Here ONLY this coaxial cable froze and confused ... it seems to me that even with "noise", there should not be such a large spread ...
But for now, I decided to trust the testimony of the tester (of course, having correctly connected it to the ZIF panel and removed my hands away)
---------------------------------
Tell me more please. On page 317 Your options for BGR display - ST7735_BGR_en.zip is this the final option for G328A(BGR)? Those. Can I reflash this k-version over 1.13 color?
-------------------------------------
I have the m-firmware version 1.44 extreme .... still available

[elecdonia]

Just got mine after 3 weeks. It has an unmarked microcontroller. By the looks of it, it seems like a 32pin deal. Is there a way to know which of the clones this is ?

That is a Logic Green LGT8F328P MCU. It is said to be "almost" compatible with the Atmel ATmega328P. However the pinout is slightly different. As of yet there really isn't any fully tested OSHW Transistor Tester software for it, although this person is working on it:
     https://github.com/DurandA/transistor-tester-lgt328p

I have also read discussions stating "it may be possible to rework the PC board for Atmel ATmega328P."

[hojnikb]

Just got mine after 3 weeks. It has an unmarked microcontroller. By the looks of it, it seems like a 32pin deal. Is there a way to know which of the clones this is ?

That is a Logic Green LGT8F328P MCU. It is said to be "almost" compatible with the Atmel ATmega328P. However the pinout is slightly different. As of yet there really isn't any fully tested OSHW Transistor Tester software for it, although this person is working on it:
     https://github.com/DurandA/transistor-tester-lgt328p

I have also read discussions stating "it may be possible to rework the PC board for Atmel ATmega328P."

cool. Did anyone try this modified firmware... Does it actually work?
How does one go about flashing these things.... likely not serial, like arduinos?

[Feliciano]

We could review/update some discussion of last year about the several MCU clones populating the market, and DurandA initiative. If we re-read the discussion around those days, maybe there is something worthy to add now.

[elecdonia]

cool. Did anyone try this modified firmware... Does it actually work?
How does one go about flashing these things.... likely not serial, like arduinos?

I don’t know very much about the DurandA project on GitHub. It hasn’t been updated in 2 years. Perhaps the author went on to other projects before finishing it? There seem to quite a few unfinished projects on GitHub.

Programming LGT8F328 chips is totally different than Atmel AVR.
The AVR programming interface is known as “ISP” and uses a 6-pin cable and a programming device.
Arduino boards have a “bootloader” which works through a TTL level or USB serial port.
But to get the bootloader onto an AVR initially requires the ISP programmer.
LGT8F328 uses a totally different programming device than AVR.

Note: Transistor Testers don’t usually have a bootloader. There’s not enough flash in 32k devices like ATmega328P or ATmega324 for them to have a bootloader and still have enough room for the Transistor Tester firmware.

[.RC.]

My LCR testers turned up today.

While the chip says Atmel 328P and it did come from what should have been a reputable seller (fnirsi)  There is no crystal on the board, so I am going hmm.

[indman]

.RC.,you got a fake from FNIRSI!

[.RC.]

Well a fake there.

Then I try to use the second one I bought and it is DOA.

Not even the screen lights up when I connected a battery and tried to test a resistor.

Just not my day.

[indman]

Not even the screen lights up when I connected a battery and tried to test a resistor.

In this option, a lot depends on how thoroughly and carefully you assembled the constructor.
Before soldering parts, it is highly desirable to check their compliance with the diagram and item number.
Very rarely, but there have been cases that the ATMEGA328 was empty. Then you need a simple programmer to determine this.

[elecdonia]

Then I try to use the second one I bought and it is DOA. Not even the screen lights up when I connected a battery and tried to test a resistor. Just not my day.

Two months ago I purchased a Transistor Tester in  “kit form” identical to the unit in your photo. I thought it was easy to assemble, but then I’m a professional EE with many years of experience.

Before starting the build I took several photos of the bare PC board since it has the labels showing where each component part is supposed to go. Then I measured the resistors with ohmmeter and put them into groups of same resistance before soldering to PC board. These resistors are small and the color bands can be difficult to read.

After assembly the LCD would turn on and display the expected screens. It was almost functional. However it was unable to enter the “self test”  mode. Then I discovered that one of the 680 ohm “probe” resistors was slightly out of spec. Details are in my previous post:

https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/msg4726172/?topicseen#msg4726172

I strongly recommend downloading the full Transistor Tester manual and then printing the schematic and selected pages to use while troubleshooting. I will endeavor to post a brief checklist to assist with getting these “kit form” Transistor Testers into working condition.