$20 LCR ESR Transistor checker project

[elecdonia]

MrAl,why did you provide us with a full copy of the message February 23, 2013 from the 1st page of the topic? You could just make a short link to this post in the topic.

What is the method to insert links to other posts which are inside the EEVblog forums? The only instructions I can find in the forum help documents are for linking to URLs. I can do that OK. But I cannot yet link to an individual forum post. 
Thanks in advance!

[indman]

elecdonia, this is easy to do if you copy the link "Re: $20 LCR ESR Transistor checker project" in the browser and paste it through the globe icon "InsertHiperlink" 
For example, here is a link to the 1st post in the topic
https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/msg195093/#msg195093

[elecdonia]

To protect U7 I will try adding a series resistor (4K7 or 10K) between the high end of 40 ohm current sensing resistor and U7 current sensing pin.

It will cause quite a big additional power consumption by device (additional 40mA or something like that).

You can put protective diode or zener diode in parallel to that 40 ohms resistor. Diode will not allow over voltage on U7 sensor pin, it will cut voltage to 0,6v.

I will test your suggestion to connect diode in parallel with 40 ohm resistor.
Advantage: Addition of parallel diode doesn’t require cutting a PC board trace.

However, addition of 10K series resistor should not cause power consumption to increase. The input resistance of U7 current sensing pin is much larger than 10K. Therefore the series resistor is not expected to alter the operation of U7.

[vklimk]

However, addition of 10K series resistor should not cause power consumption to increase. The input resistance of U7 current sensing pin is much larger than 10K. Therefore the series resistor is not expected to alter the operation of U7.

Agree. I have updated that message recently, please have a look. I think it is necessary to add one more component for a special case I didn't think about. See a drawing there as well.

By the way, if the input resistance of U7 current sensing pin is much larger than 10K then almost all voltage from capacitor will be applied to U7 current sensing pin (it will be similar to a simple resistor divider), 10K resistor will not protect U7 from overvoltage.

[elecdonia]

However, addition of 10K series resistor should not cause power consumption to increase. The input resistance of U7 current sensing pin is much larger than 10K. Therefore the series resistor is not expected to alter the operation of U7.

Agree. I have updated that message recently, please have a look. I think it is necessary to add one more component for a special case I didn't think about. See a drawing there as well.

By the way, if the input resistance of U7 current sensing pin is much larger than 10K then almost all voltage from capacitor will be applied to U7 current sensing pin (it will be similar to a simple resistor divider), 10K resistor will not protect U7 from overvoltage.

Yes, adding a small series resistance (100R) between the filter capacitor and the ZIF socket will reduce the instantaneous peak of the transient current to 300mA when a direct short is placed across K and A test pins.

Regarding current sensing pin of U7, it is possible this device has ESD protection, but dumping a capacitor charged to 30V directly into it would likely cause permanent damage. I accidentally destroyed the SRV05-4 protection device in a much older transistor tester (GM328 AY-AT type) with a capacitor which I (incorrectly) thought was discharged. The ATmega328 MCU was undamaged, so the protection circuit did protect the MCU. I temporarily removed the faulty SRV05-4 but will replace it as soon as the replacements arrive. I also ordered replacement U7 devices at the same time. I will be testing the revised circuit you recommend as soon as these arrive.

[vklimk]

Yes, adding a small series resistance (100R) between the filter capacitor and the ZIF socket will reduce the instantaneous peak of the transient current to 300mA when a direct short is placed across K and A test pins.

300mA will be applied for a very short time and will not damage the diode.
And we can increase this resistor to limit the current more. But we have to know triggering voltage for zenner diode detection to find the best value for the resistor.
Can you find this voltage?
Just remove burned u7 and connect voltage supply to K and A terminals to emulate voltage drop of zenner diode. Set 30v and slowly decrease it, TT will start detecting zenner diode at specific level. It will be near 25v most probably. Having triggering voltage we'll be able to find better value for that resistor.

[indman]

I also ordered replacement U7 devices at the same time. I will be testing the revised circuit you recommend as soon as these arrive.

For me, your efforts to restore this clone from FNIRSI look ridiculous - it's like trying to make a chocolate candy out of shit!? FNIRSI has released a crude, low-quality product to the market, which does not correspond to the level of this project in any way. It is desirable to return such products to the seller, to demand a refund of the money spent for wasting time.

[elecdonia]

Hardware upgrade and update mod m-firmware 1.43m,k-firmware 1.13k for clone LCR-TC1!

I wish I had purchased LCR-TC1 last year, back when the Asian manufacturers made them with ATmega324 MCU. Sadly it appears all LCR units available today contain an unknown MCU (frequently mislabeled ATmega328). I know of 2 ways to ID the fake MCU, but it requires seeing a photo of PC board (never shown by the Asian vendors):
   1) Pinout is totally different than Atmel MCU
   2) There is no crystal

I would have loved to do the ATmega644 mod described in detail in the following post. It has all the advanced features in a self-contained unit powered by a rechargeable battery!
https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/msg3578117/#msg3578117

FYI the Asian vendors are now offering bare ATmega324 and ATmega644 TQFP-44 MCU chips for $20-30 USD each, plus shipping. I suspect they learned the bare IC chip all by itself can now be sold for more $ than a fully assembled transistor tester. As a long-term Atmel AVR fan I’m glad I bought several tubes of AVR MCU (DIP-40) with large flash size several years ago before they became expensive, and then unavailable from USA distributors like Digikey & Mouser.

New plan: I’ll build a “full featured” transistor tester from scratch. As a consolation prize I may use a much larger TFT display panel. It will be the “bench version” rather than “handheld.”

[elecdonia]

I also ordered replacement U7 devices at the same time. I will be testing the revised circuit you recommend as soon as these arrive.

…FNIRSI has released a crude, low-quality product to the market, which does not correspond to the level of this project in any way.

Maybe FNIRSI had no official relationship at all with these recent LCR-TC1 clones?
Could it be that the LCR clone makers simply thought it would look better to display FNIRSI on the self-calibration screens?

When I ordered the LCR-TC1 (where U7 failed after I used it a couple of times) I was hoping to receive the ATmega324 unit.

From what I’ve read about FNIRSI, the stuff they make is very cheap. Some of it is said to be “functional” to a certain extent. But mostly it is just “cheap.” I won’t buy any more FNIRSI gear until their reputation improves. I own way too much test gear already. Most of it is in the “restored vintage” category.

[MrAl]

MrAl,why did you provide us with a full copy of the message February 23, 2013 from the 1st page of the topic? You could just make a short link to this post in the topic.

Oh it must have come out that way when quoted the very first post.  Not sure why the images show up again like that.  Makes it longer.
I can try to get rid of that part i guess.

[MrAl]

Also, these little meters will never be able to read inductors except for the very small ones maybe, and maybe only air core inductors. 

The Transistortester isn't an LCR meter, but in can measure L, C and R to some extend. Get one, compare the results with a proper LCR meter, and you'll see that the Transistortester isn't that bad.

For several years I’ve been using a device known as the LC100-A to measure inductors and capacitors. I highly recommend the LC100-A for measuring small capacitance and inductance - uH and pF. That said, the LC100-A is also capable of measuring 10,000uF and 50H.

The LC100-A is a modern digital version of the legendary “grid dip meter” used by ham radio enthusiasts for nearly 100 years. It tests the unknown L or C by connecting it in parallel with an internal calibrated C or L to form a tuned LC circuit. It then uses an IC comparator with positive feedback to drive the LC circuit into steady oscillation. Typical oscillation frequency is from 5kHz to 500kHz. Finally an internal MCU-based frequency counter measures the frequency of oscillation and uses clever math to calculate and display the uH or pF of the unknown L or C.

As a result of my personal experience with the LC100-A I recommend that everyone who enjoys using their transistor tester should also try out the LC100-A.

There are numerous Asian vendors for the LC100-A. Although the quality and accuracy of the LC100-A implementation varies by vendor, the cost ( < $25 USD) allows one to explore this useful device on a budget. The original manufacturer of the LC100-A is a company named Ming-He. I have a genuine branded Ming-He LC100-A which is amazingly accurate, often within 2% when compared to high-end LCR meters. If you can find a vendor who shows a photo of the LC100-A with a Ming-He label under the PC board, then this is the one to buy.

Here is a link to a more comprehensive discussion of the LC100-A from the Antique Radio forum:

https://www.antiqueradios.com/forums/viewtopic.php?f=8&t=365161


-Elecdonia

What is the excitation current adjustment range?

I cant see how any one meter will be able to measure all inductors, although it may still be useful.
For example, some buck converters will output 100ma while others 100 amps.  That means the filter inductor may be seeing either 100ma DC or 100 amps DC.  I've dealt with that entire range in my career so i can see how things can vary and how the inductance can vary.
Im not saying other meters cant help, but they will never be able to test the entire range of inductors available.  That's all.

[MrAl]

Hello there,

If you get a scope and frequency generator you can test for all those things and get the error down to a very low value.  This is especially useful for cap ESR which is an important specification.
(...)

I agree with your remarks about the potential pitfalls when measuring inductors and capacitors, but the keyword is convenience: for a quick check these testers are exceptionally useful.

Yes of course i understand that, but i wanted to make it clear that no one tester can test every inductor out there and some require a large DC bias to test properly.  For a quick example, saturation current.

I just wanted to make it clear that there will be inductors that are harder to test so they would have to be tested in the actual circuit they will be used in or a prototype of the same circuit.  That way they are subject to the same bias and frequencies and all that.

[indman]

I just wanted to make it clear that there will be inductors that are harder to test so they would have to be tested in the actual circuit they will be used in or a prototype of the same circuit.  That way they are subject to the same bias and frequencies and all that.

None of the people who understand the meaning of electronics does not argue with this opinion, it's true, but as correctly observed by dear rsjsouza - the key purpose for this project is a QUICK TEST of a part, removed from the board or a new (unknown) part. For more detailed testing and analysis you will certainly need more serious equipment.

[elecdonia]

None of the people who understand the meaning of electronics does not argue with this opinion, it's true, but as correctly observed by dear rsjsouza - the key purpose for this project is a QUICK TEST of a part, removed from the board or a new (unknown) part. For more detailed testing and analysis you will certainly need more serious equipment.

I agree 100%.

The transistor tester is intended to be the quickest, easiest, and lowest cost method to identify unknown components and provide reasonable measurements of their parameters. Often this is sufficient when diagnosing a malfunctioning circuit. Faulty components usually measure grossly out of spec. But a component which measures within +/- 20% of its expected value is likely to be functional.

Yes, "lab grade" test gear can be necessary for comprehensive design and debugging projects. However one doesn't always need expensive gear to quickly determine whether a component is good or bad. I own plenty of test gear, yet I nearly always make my "first tests" with small convenient easy-to-use tools like the transistor tester or a hand-held 3.5 digit multimeter. I also own a 6.5 digit multimeter ( HP 3456A ), but I don't use it every day.

Finally, for people with limited budgets and for folks who are just starting out with electronics, low-cost multi-function test gear like the transistor tester is essential.

[elecdonia]

What is the excitation current adjustment range?

I cant see how any one meter will be able to measure all inductors, although it may still be useful.
For example, some buck converters will output 100ma while others 100 amps.  That means the filter inductor may be seeing either 100ma DC or 100 amps DC.  I've dealt with that entire range in my career so i can see how things can vary and how the inductance can vary.
Im not saying other meters cant help, but they will never be able to test the entire range of inductors available.  That's all.

I value your comments about L & C measurement and wish to continue this discussion in greater depth.
Therefore let’s move our discussion to the following topic which is focused on L/C measurement devices such as the LC100-A:

https://www.eevblog.com/forum/testgear/lc100-a-a-precise-lc-meter-for-3-75$/msg4596301/#msg4596301

[indman]

One of the new clones of the Chinese industry and its inner world. The marking of the chips is smeared, but if we compare the location of 6 external measuring resistors, we can assume that the Chinese LGT8F328P controller or its equivalent is used.
The photos are not mine.

[elecdonia]

I finally took the plunge and got a random version from eBay. From the outside this looks identical to the LCR-TC1 version but inside it has the same PCB as LCR-T7(FNIRSI) AFAICS complete with a (presumably fake) chip marked as MEGA328P. When you power it up in test mode it says FNIRSI-TC1, pauses at 38% but it does not report the firmware version at the end. I was hoping to reflash it, never mind.

I got a similar unit a couple of weeks ago. It works but... I wanted a unit with ATmega324 so I could change the MCU to ATmega644 and gain a lot more functionality in a self-contained battery-powered unit. This post describes the mod I want to do:
     $20-lcr-esr-transistor-checker-project/msg3578117
 
But... No luck!
Yesterday I ordered another unit which just might contain the ATmega324. These things are cheap enough that I'll keep at it until I get the one I want!

FYI these forum posts suggest the fake ATmega328 is actually a APT32F172K8T6 :
     $20-lcr-esr-transistor-checker-project/msg4291063
     $20-lcr-esr-transistor-checker-project/msg4370932
     $20-lcr-esr-transistor-checker-project/msg4383955 
     $20-lcr-esr-transistor-checker-project/msg4398580
     $20-lcr-esr-transistor-checker-project/msg4429093

Also take a look at the attached pinouts. They are totally different! In fact the VDD and VSS pins are on opposite sides of the package! The only thing they have in common is that both MCU chips are in a 32-pin TQFP package.

[Spongey]

I found out two other things about the fake TC1.

It sends traffic down the serial port (which is connected to the USB port via a CH340N) at various points, such as pressing the button, making a measurement and decoding IR. Not readable text though.

Pressing the button 4 times rapidly puts in into a bootloader screen. Not managed to do anything else at that point. After 5 minutes (or disconnecting the battery) it resumes normal operation.

[elecdonia]

One of the new clones of the Chinese industry and its inner world. The marking of the chips is smeared, but if we compare the location of 6 external measuring resistors, we can assume that the Chinese LGT8F328P controller or its equivalent is used.
The photos are not mine.

RE: This LGT8F328P clone of the Atmel ATmega328 MCU:
     Evidently this MCU has been ported into the Arduino IDE.
     It is also claimed that clone Arduino boards are available with this LGT8F328P MCU.
     I intend to get some for experimentation since they cost almost nothing.
     I'm intrigued by its (claimed) 32MHz clock option.

The following links may be useful:
     projects/anyone-here-interested-in-the-logic-green-avrs-lgt8f328p
     microcontrollers/lgt8f328p-clone-of-atmega328-with-lots-of-extras-anybody-use-them

Also a suggestion for searching for this MCU on EEVblog: Try both of these search terms: LGT8F328P and LG8F328 (without P at the end), and also search for "logic green" (manufacturer of the LGT8F328P)

[elecdonia]

I found out two other things about the fake TC1. It sends traffic down the serial port (which is connected to the USB port via a CH340N) at various points, such as pressing the button, making a measurement and decoding IR. Not readable text though. Pressing the button 4 times rapidly puts in into a bootloader screen. Not managed to do anything else at that point. After 5 minutes (or disconnecting the battery) it resumes normal operation.

My LCR-TC1 FNIRSI responds to the "quickly press the button 4 times" command as seen in the attached photo. It displays FNIRSI-TC1 in the bootloader screen. It also displays FNIRSI-TC1 at the start of the selftest procedure. I haven't yet checked for any output from the USB port.

-E

[eti]

How does one know if this model uses genuine part? Photo shows 32 pin atmega…

ARCELI LCR-T4 ESR Meter Transistor Tester Diode Triode Capacitance SCR Inductance https://amzn.eu/d/g9qNQx6

[madires]

It's a lottery. Even when the images show a genuine ATmega it doesn't mean that you'll get one with your new tester. One of the replacement MCUs has a different pinout (check Vcc and Gnd). The other one often has fake markings with a specific batch number and production date code (was posted a while ago).

[vklimk]

PCB in the photos has ISP header specific for atmega MCU. So, if your PCB is identical to the photo then most probably it will be atmega MCU.

[elecdonia]

How does one know if this model uses genuine part? Photo shows 32 pin atmega…
ARCELI LCR-T4 ESR Meter Transistor Tester Diode Triode Capacitance SCR Inductance https://amzn.eu/d/g9qNQx6

The unit in the Amazon photos has a genuine ATmega328 MCU. Because it’s coming from Amazon you can return it if it doesn’t look exactly like the photo.

One other thing: This unit does not have a protection circuit for the MCU. So be sure to discharge all capacitors before connecting them to the tester.

[elecdonia]

It's a lottery. Even when the images show a genuine ATmega it doesn't mean that you'll get one with your new tester.

The following post contains the most recent (16 Dec 2022) clone identification and comparison list. I think it is the best available reference to identify different versions of the transistor tester:

$20-lcr-esr-transistor-checker-project/msg4584517