$20 LCR ESR Transistor checker project

[elecdonia]

I have ordered a through hole DIY kit.  Is it worth it doing the things in this mod just for general use?  https://github.com/blurpy/transistor-tester

That’s a very good set of recommendations. Note that it begins by explaining the importance of matching the probe resistors. Especially the three 680 ohm probe resistors. They don’t need to be precisely 680 ohms, but they need to match each other within +/- 0.5 ohms. The three 470k ohm probe resistors also need to match each other. Unfortunately the resistors which come with these kits usually aren’t matched. Replacing these six resistors with high-quality 0.1% precision resistors is a great place to start.

[madires]

is this a full version of the LCR ESR Transistor Tester Project?

No, it's my 644 developement board (https://github.com/madires/Transistortester-Warehouse/blob/master/Hardware/DevKit-644.kicad.tgz) and a display board with level shifters. The dev board features the Zener check with boost converter, rotary encoder, 2.5V reference, self-adjustment cap, SRV05-4 input protection and the SamplingADC cap.

[oitar]

Hi all, sorry- tried reading the whole forum, but it will take a few months..

I have a LCR-TC2 with a Mega324PA cpu, on a T7-plus V1.1 board, 6 pin connector to 160x128 display subboard.
Originally was showing v3.1E firmware, but had a very bad(although consistent) accuracy on certain resistor values only, and very low reading on zeners below 10V(showing less than 1V). Input ports were not blown- confirmed it by measuring equal resistance of few hundred kOhm to Vcc and Gnd.

Soldered headers for main cpu, and U3(in my case), tried a few pre-compiled firmware(.hex and .eep) files without success. Best I can get is startup, quick measurement, and then almost immediate off(with v1.34m).
Is there any alternative firmware for the U3 chip? It gets recognized by STC-ISP as STC15L104W, but the only firmware I have is tc1_u4_v0.3.1.hex(which flashes without error). Or is it the main program that's not right?

If I need to compile from a source file, why are there no mega324 subfolders inside the trunk folders of both developers?
Sorry about the noob questions, but have been battling for few days.

[madires]

Is there any alternative firmware for the U3 chip? It gets recognized by STC-ISP as STC15L104W, but the only firmware I have is tc1_u4_v0.3.1.hex(which flashes without error). Or is it the main program that's not right?

Nope, the STC15 firmware from https://github.com/atar-axis/tc1-u4 should also work for your tester. Alternatively you could replace U3 with a simple two-transistor circuit (https://github.com/madires/Transistortester-Warehouse/blob/master/Hardware/TC1-Mod.pdf). And yes, the m-firmware could be configured incorrectly. In the source archive is a file called 'Clones' which lists the recommended settings for various clones, including the TC family.

If I need to compile from a source file, why are there no mega324 subfolders inside the trunk folders of both developers?

The k-firmware needs a small modification for the ATmega324 (see https://www.eevblog.com/forum/testgear/$20-lcr-esr-transistor-checker-project/msg4637602/#msg4637602] and the next few posts). And the m-firmware doesn't provide any binaries as there are too many configuration possibilities.

[elecdonia]

The dev board features the Zener check with boost converter, rotary encoder, 2.5V reference, self-adjustment cap, SRV05-4 input protection and the SamplingADC cap.

I’ve read many posts claiming the “2.5V reference IC isn’t needed if the 5V regulator is very precise in voltage and free of drift.”

What is your current opinion about this?

[madires]

Still the same, i.e. the external 2.5V voltage reference should be at least 10 times more precise than the 5V voltage regulator to make sense. The dev board has an external reference for testing purposes (in this case an LM4040).

[Fuzzy Star]

...it's my 644 developement board... features the Zener check with boost converter, rotary encoder, 2.5V reference, self-adjustment cap, SRV05-4 input protection and the SamplingADC cap.

I'm curious about the MCP1702 at the boost converter input. Any reason to use that precision regulator there instead of an AMS1117-5.0 or 78L05?

Also curious about the 'logic probe' option. Do you think about including that circuit on the dev kit schematic?

The 'SamplingADC cap relay' option is on the schematic but firmware files say 'not suppoted yet', 'not implemented yet'. Is there any developement about it?

[madires]

Any 5V regulator is fine. I simply had a bunch of MCP1702s at hand. The logic probe option is a dedicated ADC pin with a voltage divider, quite easy to add. I don't think I'll add it to the dev kit to keep one ADC pin free for testing future options. The SamplingADC is currently supported only by the k-firmware, and I don't have any plans to add it to the m-firmware any time soon. Also, I don't know if Karl-Heinz already added support for the cap relay option.

[9voltbrain]

About the LCR-T7... The rechargeable battery is making me a little paranoid, plus I think it's annoying having to keep it charged, so I'm thinking of replacing it with AAA-batteries. How hard would this be? Would I need to regulate the voltage down from 4.5 volts (3xAAA), or can it handle 4.5? The rechargeable battery is 3.7v.

[gipetto]

i saw a post saying the stc chip in the t7 is only rated for 3v max, and so using it with a 3.7v li ion is overdriving. in that case, two aa cells in series would be sufficient.when (if) mine arrives i may do as others did and use a switch in series with the battery to prevent discharge if it is an issue. aa cells are expensive, i think you would be going backwards.

[Feliciano]

About the LCR-T7... The rechargeable battery is making me a little paranoid, plus I think it's annoying having to keep it charged, so I'm thinking of replacing it with AAA-batteries. How hard would this be? Would I need to regulate the voltage down from 4.5 volts (3xAAA), or can it handle 4.5? The rechargeable battery is 3.7v.

• The battery draining is annoying if you have one of the old versions in original state (with the STC power management MCU). That can be solved by replacing it with 2 transistors (plus some dioes and resistors) and flashing the m-firmware, with many other benefits discussed in this thread
• If you have one of the recent versions, the battery doesn't drain too fast (unless yours is damaged somehow)
• To feed the ctester with something less than 5V, and variable (as batteries goes flat) would give you all sort of troubles. For starter remember this is comparing voltages samples against references. So I would rather find a bigger Li-Ion battery and/or modify the circuit as I stated above. But if you really want to use AAA size, I would analize whether the existing charger/boost converter could handle that scenario

[thm_w]

Can't believe there is still no STM32 or other high end port of this tester. Some regular alix models are selling for $30.
Usually Chinese products are very quick to swap out the micro to a completely different model. But maybe the atmega clones are so cheap there is no incentive.

Anyone here working on it?

[9voltbrain]

About the LCR-T7... The rechargeable battery is making me a little paranoid, plus I think it's annoying having to keep it charged, so I'm thinking of replacing it with AAA-batteries. How hard would this be? Would I need to regulate the voltage down from 4.5 volts (3xAAA), or can it handle 4.5? The rechargeable battery is 3.7v.

To feed the ctester with something less than 5V, and variable (as batteries goes flat) would give you all sort of troubles. For starter remember this is comparing voltages samples against references. So I would rather find a bigger Li-Ion battery and/or modify the circuit as I stated above. But if you really want to use AAA size, I would analize whether the existing charger/boost converter could handle that scenario[/li][/list]

The battery that comes with it is already lower than 5V (3.7), so how would this be more of an issue with AAA? When the battery voltage drops too low for it to regulate to its desired operating voltage, it's going to tell me to "charge", then I'll just change the batteries. Am I missing something?

[elecdonia]

Can't believe there is still no STM32 or other high end port of this tester. Some regular alix models are selling for $30.
Usually Chinese products are very quick to swap out the micro to a completely different model. But maybe the atmega clones are so cheap there is no incentive.
Anyone here working on it?

In the existing Transistor Tester hardware architecture several MCU I/O pins are directly connected to the 3 probe terminals (or connected through the 680 ohm and 470k ohm probe resistors). This requires the MCU to directly support 5V I/O for digital outputs and inputs. Also the on-chip A/D converter needs to accept 0-5V. If the test voltages were limited to 3V it would become impossible to test most transistors, JFETs, and MOSFETs.

A substantial amount of additional analog driver and level-shifting hardware will be necessary to make the Transistor Tester concept functional with a 3V MCU. It will no longer be a “simple” circuit design where the MCU itself does most of the work.

With that said, if  an analog driver section was to be developed it would be feasible to support testing with voltages >5V.

[thm_w]

Can't believe there is still no STM32 or other high end port of this tester. Some regular alix models are selling for $30.
Usually Chinese products are very quick to swap out the micro to a completely different model. But maybe the atmega clones are so cheap there is no incentive.
Anyone here working on it?

In the existing Transistor Tester hardware architecture several MCU I/O pins are directly connected to the 3 probe terminals (or connected through the 680 ohm and 470k ohm probe resistors). This requires the MCU to directly support 5V I/O for digital outputs and inputs. Also the on-chip A/D converter needs to accept 0-5V. If the test voltages were limited to 3V it would become impossible to test most transistors, JFETs, and MOSFETs.

A substantial amount of additional analog driver and level-shifting hardware will be necessary to make the Transistor Tester concept functional with a 3V MCU. It will no longer be a “simple” circuit design where the MCU itself does most of the work.

With that said, if  an analog driver section was to be developed it would be feasible to support testing with voltages >5V.

Yeah I did see a bit about that earlier but your explanation is much clearer, thank you.
It would be cool to have more than 5V available on all of the testing pins, on a higher end version. IMO.

There is also say the ATSAMC20G18A, instead of STM32, which can do 5V.

Looks like the $100 Peak DCA55 only supports 5V as well.

[gipetto]

there are 8051 mcus widely available. they tend to be more ram limited than the current atmega (300 bytes) due to  their age, but they're much cheaper. some have 64k of flash. If you wanted to avoid the scarcity issue it would be a good way to go.

[indman]

Can't believe there is still no STM32 or other high end port of this tester. Some regular alix models are selling for $30.
Anyone here working on it?

There is such a port and it is called DSO-TC2. And now, Chinese friends have launched an updated version of DSO-TC3 on the market, in which they added a signal generator and also taught how to measure the ESR of capacitors.
It is interesting to look at the circuitry of this clone and find out how it is possible to match the power supply of the STM with checking parts with a higher voltage? 

[Feliciano]

The battery that comes with it is already lower than 5V (3.7), so how would this be more of an issue with AAA? When the battery voltage drops too low for it to regulate to its desired operating voltage, it's going to tell me to "charge", then I'll just change the batteries. Am I missing something?

Similar to a power bank, your ctester comes with a 3.7V Li-Ion charger and boost converter to 5V, designed to operate within 4.2V to 3.2V or so. A new set of 3x AAA can be between 4.8V full or 2.7V flat.

As I said, if you connect the alkaline batteries directly to the main MCU you will have a lot of trouble. And if you connect it to where the actual battery is, you would have to check whether that IC supports 5V Vbatt (and put a tape over the microUSB input), and how it would be behave under that scenario.

Let's say it does: If your ctester shut off at 3.5V, you would be replacing alkaline batteries with around 45% of charge remaning.

[madires]

About the LCR-T7... The rechargeable battery is making me a little paranoid, plus I think it's annoying having to keep it charged, so I'm thinking of replacing it with AAA-batteries. How hard would this be? Would I need to regulate the voltage down from 4.5 volts (3xAAA), or can it handle 4.5? The rechargeable battery is 3.7v.

You could add a simple switch to prevent discharging by the control MCU. When going for the AAA batteries check if the Li-Ion charger chip will be happy with the higher voltage or needs to be removed. The second thing to check is the control MCU. The STC15L104W is rated for 2.4 to 3.6V (STC15F104W 3.8 - 5.5V).

[Cliff Matthews]

Can't believe there is still no STM32 or other high end port of this tester. Some regular alix models are selling for $30.
Anyone here working on it?

There is such a port and it is called DSO-TC2. And now, Chinese friends have launched an updated version of DSO-TC3 on the market, in which they added a signal generator and also taught how to measure the ESR of capacitors.
It is interesting to look at the circuitry of this clone and find out how it is possible to match the power supply of the STM with checking parts with a higher voltage? 

TC3 first looks here I think

[Fuzzy Star]

Thanks for the answers, Madires.

Any 5V regulator is fine. I simply had a bunch of MCP1702s at hand.

Just noticed the 'Extented circuit with ATmega644' in Karl-Heinz's pdf document also has MCP1702 in the same place.

The logic probe option is a dedicated ADC pin with a voltage divider, quite easy to add. I don't think I'll add it to the dev kit to keep one ADC pin free for testing future options.

Yes, the voltage divider is easy to add. I just thought seeing the options on the schematic would be better than discovering them inside the firmware files.

The SamplingADC is currently supported only by the k-firmware, and I don't have any plans to add it to the m-firmware any time soon. Also, I don't know if Karl-Heinz already added support for the cap relay option.

As far as I see there is no mention of cap relay in the k-fw makefile and config files.

I also noticed the 'extented circuit' schematic uses a darlington BJT for 'power management', your dev-kit schematic has a standard BJT there. I imagine it's just preference.

[gipetto]

i received my joyit lcr-t7 from reichelt.de today. i tried the self test with the three terminals shorted but it pauses indefinitely at 26% unless the short is removed. the pcb is the same as the previous user posted, with the dip mcu.
I guess if i want to calibrate it i'd have to change a resistor somewhere to get the self test to run. i dont plan to do so because smt is painful for me, and if i put a through hole part on it would surely tear the traces.

[madires]

Yes, the voltage divider is easy to add. I just thought seeing the options on the schematic would be better than discovering them inside the firmware files.

True! I'll add a simple diagram to the README file.

I also noticed the 'extented circuit' schematic uses a darlington BJT for 'power management', your dev-kit schematic has a standard BJT there. I imagine it's just preference.

Yep, any PNP with a sufficient high hFE and current rating is fine.

[madires]

i received my joyit lcr-t7 from reichelt.de today. i tried the self test with the three terminals shorted but it pauses indefinitely at 26% unless the short is removed.

Around 22% the tester will ask to remove the short (small text below the progress bar). It's part of the normal self-adjustment.

I guess if i want to calibrate it i'd have to change a resistor somewhere to get the self test to run. i dont plan to do so because smt is painful for me, and if i put a through hole part on it would surely tear the traces.

If the tester has an ATmega you can flash the original OSHW firmware with much more features.

[mcgyvr81]

i received my joyit lcr-t7 from reichelt.de today. i tried the self test with the three terminals shorted but it pauses indefinitely at 26% unless the short is removed. the pcb is the same as the previous user posted, with the dip mcu.
I guess if i want to calibrate it i'd have to change a resistor somewhere to get the self test to run. i dont plan to do so because smt is painful for me, and if i put a through hole part on it would surely tear the traces.

No, this is standard behaviour of this tester. It requires 1,2,3 to be shorted upon startup to enter self-test mode, then have the short removed when requested to complete the test. This happens to be at 26% on my unit as well - it flashes the request to remove the short on the bottom of the screen when it's waiting for it.