$20 LCR ESR Transistor checker project

[Per Hansson]

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.

Well duh, you have to solder the components to the PCB first!
Sorry, I'll find the door and let myself out

[alex_D]

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.

Worth looking at this video for troubleshooting:-
  #108 Building and testing an eBay Transistor Tester kit
Also feel free to post some closeup photos of the assembled board in case we can spot something.

[.RC.]

Well duh, you have to solder the components to the PCB first!
Sorry, I'll find the door and let myself out

Oh, damn, I thought I must have done something wrong.   

There is another job to do.

Actually I was going to get some high precision components for the kit before I built it.

[vk3em]

I ordered a LCR-TC2 from SeeSensor on AliExpress which arrived today.
https://www.aliexpress.com/item/1005004717377243.html

PCB is marked T7 Plus v2.0 - mcu has no markings, 8 pins per side.

Note: This seller was previously known to ship Atmel based LCR testers (at least in Jan 2023) but now in April 2023 they have moved to the alternative.

[elecdonia]

I ordered a LCR-TC2 from SeeSensor on AliExpress which arrived today.
     https://www.aliexpress.com/item/1005004717377243.html
PCB is marked T7 Plus v2.0 - mcu has no markings, 8 pins per side.
Note: This seller was previously known to ship Atmel based LCR testers (at least in Jan 2023) but now in April 2023 they have moved to the alternative

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."

[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.

After looking at your photo very closely I think I understand the problem.

[.RC.]

After looking at your photo very closely I think I understand the problem.

Yes, there is no crystal there either, or so I found out when I was going through the components.

So I visited Ms Mouser and ordered all the parts to make it as per the proper original specs.  I actually ordered twice the number (plus some other stuff I needed) as then I got free freight, as otherwise the freight was more then the component costs. Only thing I could not get was a spare dip ATMega328 as they were out of stock.

I will probably blow this unit up down the track doing something silly.   Probably worth getting another kit anyway as who knows how long these genuine Atmel kits will be around for.  It seems the prebuilt SMD units are pretty much non Atmel now, unless you are lucky. 

[vk3em]

Probably worth getting another kit anyway as who knows how long these genuine Atmel kits will be around for.

Where can you buy it from?

Luke

[elecdonia]

Yes, there is no crystal there either, or so I found out when I was going through the components.

The standard factory crystal is 8MHz. That's what my "kit form" unit came with. Only part "missing" from my unit was a 10k resistor which I had dropped on the floor (I did manage to find it).

[.RC.]

Where can you buy it from?

Luke

I generally buy from Aliexpress now.   Seems to be far cheaper then ebay for me.

I searched with this term GM328 LCR tester  -->> https://www.aliexpress.com/w/wholesale-gm328-lcr-tester.html

I did some searching and found one seller selling a kit for a far lower price then everyone else.   Then I noticed the three SMD components on the PCB were missing in the photo -->> https://www.aliexpress.com/item/32706710335.html

I also found a version that looked to be a cut down version. 

So I went for a version were multiple sellers were around a similar price.  Like -->>https://www.aliexpress.com/item/1005003127524856.html

[hoangtran]

I ordered a LCR-TC2 from SeeSensor on AliExpress which arrived today.
https://www.aliexpress.com/item/1005004717377243.html

PCB is marked T7 Plus v2.0 - mcu has no markings, 8 pins per side.

Note: This seller was previously known to ship Atmel based LCR testers (at least in Jan 2023) but now in April 2023 they have moved to the alternative.

I have the same item like this. Mod to Atmega328 with 1.48m firmware. Here is the result:
Original firmware:

M328 with 1.48m firmware

Measuring with DE5000

[Yuriy_K]

I have the same item like this. Mod to Atmega328 with ...

The value of any measuring instrument is determined by its accuracy in relation to reference values.
I did not find a similar capacitor in my arsenal. For example, the readings of such capacitors on the firmware of both authors.

[hoangtran]

In my pics, there is a big difference in ESR measuring between the original firmware (8.19 ohm) and the m firmware (0.14 ohm). And the ESR results of m firmware and DE-5000 are nearly equal.

[Feliciano]

Have you calibrated the component tester before and after flashing the OSHW firmware? and again when alternating between the ZIF socket and the test leads? This is an important step to do every time to change the environment.

[elecdonia]

In my pics, there is a big difference in ESR measuring between the original firmware (8.19 ohm) and the m firmware (0.14 ohm). And the ESR results of m firmware and DE-5000 are nearly equal.

Regarding Transistor Testers with their original Chinese factory firmware:

It is always necessary to "short the probes" and then press "Start" to perform the "self-test" before expecting accurate test results. Chinese firmware performs "self-test" for 15 to 60 seconds and then displays a message instructing the user to "isolate probes" (remove the short) and then the self-test continues for another 20 to 60 seconds before it finishes. Unlike open-source Transistor Tester firmware the Chinese firmware does not display intermediate "step-by-step" data screens during self-test. It may be necessary to perform "self-test" several times before getting accurate test results.

Many Transistor Testers with Chinese firmware are capable of selecting either English or Mandarin for the displayed language. This is (of course) desirable for Transistor Testers which are sold both inside Chinese-speaking countries and exported. For example I have an LCR-TC1 unit (MCU is LGT8F328P) where holding down "Start" button for 5 to 10 seconds changes the displayed language between English and Chinese characters.

Because Chinese display fonts occupy a substantial amount of flash, the Chinese software developers must remove large portions of the original Transistor tester code and/or greatly simplify it.

This most certainly impacts their accuracy and reduces their feature sets.

[hoangtran]

In my pics, there is a big difference in ESR measuring between the original firmware (8.19 ohm) and the m firmware (0.14 ohm). And the ESR results of m firmware and DE-5000 are nearly equal.

Regarding Transistor Testers with their original Chinese factory firmware:

It is always necessary to "short the probes" and then press "Start" to perform the "self-test" before expecting accurate test results. Chinese firmware performs "self-test" for 15 to 60 seconds and then displays a message instructing the user to "isolate probes" (remove the short) and then the self-test continues for another 20 to 60 seconds before it finishes. Unlike open-source Transistor Tester firmware the Chinese firmware does not display intermediate "step-by-step" data screens during self-test. It may be necessary to perform "self-test" several times before getting accurate test results.

Many Transistor Testers with Chinese firmware are capable of selecting either English or Mandarin for the displayed language. This is (of course) desirable for Transistor Testers which are sold both inside Chinese-speaking countries and exported. For example I have an LCR-TC1 unit (MCU is LGT8F328P) where holding down "Start" button for 5 to 10 seconds changes the displayed language between English and Chinese characters.

Because Chinese display fonts occupy a substantial amount of flash, the Chinese software developers must remove large portions of the original Transistor tester code and/or greatly simplify it.

This most certainly impacts their accuracy and reduces their feature sets.

In this Chinese firmware, it looks like self-calibration has been cut off. I have tried many times, but only this result appears:

[hoangtran]

Have you calibrated the component tester before and after flashing the OSHW firmware? and again when alternating between the ZIF socket and the test leads? This is an important step to do every time to change the environment.

Yes, I know, but 8.19 ohm vs 0.14 ohm is not acceptable. And most importantly, I cannot run self-calibration with this Chinese firmware; it looks like they cut off that function.

[elecdonia]

In this Chinese firmware, it looks like self-calibration has been cut off. I have tried many times, but only this result appears

Please measure resistance of each 680 ohm probe resistor. There are 3 of these, each connected between a MCU pin and a test socket pin.

These 3 resistors must match each other within +/- 1 ohm.

I had a similar issue with a “kit” style Transistor Tester where the 3 resistors supplied with the kit measured as follows:  675, 676, 691 ohms. The resistor which measured 691 ohms was far enough out of range to  prevent my tester from entering “self test” mode. Instead, when powered up with 1-2-3 shorted it would only display the following test result:    “1 - [resistor] - 2 - [resistor] - 3”

Details in my earlier post:
   https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/msg4726172/#msg4726172

[Aldo22]

Please measure resistance of each 680 ohm probe resistor. There are 3 of these, each connected between a MCU pin and a test socket pin.

Hi!
Because of your posting, I looked at the circuit board of the TC1 with the APT32F172K8T6 again.
It looks like the middle "1" connectors go somewhere different than the first "1".
The first goes to R4 (474 Resistor), while the middle ones go to U6 ("V05").
I can't see what's happening on the other side of the board because that's where the connector is soldered, but to me it looks like there are different "1"s.
Does anyone understand what's going on here?
Thank you.

[madires]

Have you checked for continuity between all the #1 test pins? U6 plus D1 is the overvoltage protection. Each test pin should be connected to an ADC pin, a 680 Ohms resistor, a 470 kOhms resistor, and one I/O pin of the SRV05-4 (U6).

[Aldo22]

Have you checked for continuity between all the #1 test pins?

No, I have not. I was just looking at a photo of the inside of my device that I took earlier.
I've opened it up again now and checked continuity.
You're right, all #1's are connected.
On this occasion I also measured all resistors.
They are very close together (<1%).
Everything's ok.

Thank you!

[vk3em]

I have the same item like this. Mod to Atmega328 with 1.48m firmware. Here is the result:

Can you provide details on how you modded to replace this mcu with the ATMEGA328?

Luke

[hoangtran]

In this Chinese firmware, it looks like self-calibration has been cut off. I have tried many times, but only this result appears

Please measure resistance of each 680 ohm probe resistor. There are 3 of these, each connected between a MCU pin and a test socket pin.

These 3 resistors must match each other within +/- 1 ohm.

I had a similar issue with a “kit” style Transistor Tester where the 3 resistors supplied with the kit measured as follows:  675, 676, 691 ohms. The resistor which measured 691 ohms was far enough out of range to  prevent my tester from entering “self test” mode. Instead, when powered up with 1-2-3 shorted it would only display the following test result:    “1 - [resistor] - 2 - [resistor] - 3”

Details in my earlier post:
   https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/msg4726172/#msg4726172

I have read your post before. Those resistors in my kit are good: 680, 680, 680.01.

[hoangtran]

I have the same item like this. Mod to Atmega328 with 1.48m firmware. Here is the result:

Can you provide details on how you modded to replace this mcu with the ATMEGA328?

Luke

Yes, I can.

In the hardware: Replace LGT8F328P with ATmega328P. Wiring pin 3 and 21 to GND; pin 6 and 18 to +5V.

Here is a change in makefile:

Code: [Select]

FREQ = 16

In config.h

Code: [Select]

#define HW_REF25
#define ZENER_R1         100000
#define ZENER_R2         10000
#define ZENER_UNSWITCHED
#define ZENER_BOOST_HIGH                  /* high active */
#define HW_PROBE_ZENER
#define ZENER_VOLTAGE_MAX     20000     /* max. voltage in mV */
#define HW_IR_RECEIVER
#define UI_ZENER_DIODE
#define BAT_DIRECT
#define BAT_OFFSET       0
#define BAT_WEAK         3600
#define BAT_LOW          3400
#define ADC_LARGE_BUFFER_CAP

In config_328.h

Code: [Select]

/*
 *  ST7735
 *  - 4 wire SPI interface using bit-bang SPI
 */
#define LCD_RES          PD1            /* port pin used for /RESX (optional) */
//#define LCD_CS           PD5            /* port pin used for /CSX (optional) */
#define LCD_DC           PD2            /* port pin used for D/CX */
#define LCD_SCL          PD4            /* port pin used for SCL */
#define LCD_SDA          PD3            /* port pin used for SDA */
#define LCD_FLIP_X                      /* enable horizontal flip */
//#define LCD_FLIP_Y                      /* enable vertical flip */
#define LCD_LATE_ON                     /* turn on LCD after clearing it */

#define TP_REF           PC5       /* test pin for 2.5V reference and relay */
#define TP_BAT           PC4       /* test pin for battery */
#define TEST_BUTTON      PD5       /* test/start push button (low active) */
#define IR_DATA          PD0       /* data signal */
#define BOOST_CTRL       PD7       /* control pin */

You can play around with other options as you want.

The schematic is based on MrSqueaky's work.

[Vitaly_Ne]

There was a need to measure megaohm resistors, and noticed a nuance. It immediately shows, for example, 4470k, and then at first faster, and then it grows more slowly ... after a minute, about 4495k ... if you wait even longer from about 2 minutes, it can grow to 4497k ... and stops.
Interested in the question: is this normal for measurements? if so, is it really necessary to measure large resistances for 2 minutes? Or is it some kind of accumulation in the controller (or a failure ... although everything else measures correctly ...)? When can a measurement be considered more or less correct? At the very end or when it starts to "slow down"?
I don't attach a photo, but I can, if necessary)))
I measured on different megaohm resistors ... 0.125W, 0.5W, 1W ..
The denominations are also from 2M to 4.7M ... everything is about the same in time ..
I apologize if this has been explained before (tell me the page?) .. just for the first time I measured megaohms, so it was embarrassing ...
Tester G328A(BGR), firmware 1.13 color(from Yuriy_K).