$20 LCR ESR Transistor checker project

[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.

[indman]

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.

This is how the new DSO-TC3 measures the ESR of capacitors. While the Chinese friends have a lot of work to achieve similar results on the classic AVR. In the meantime, the ESR of this device shows the weather on Mars and not the actual equivalent resistance values.
However, like other similar testers that are not built on the original ATMEL.
In the photo, for comparison, the measurement of the same capacitor with the mod m-firmware 1.48m.

[Yuriy_K]

This is how the new DSO-TC3 measures the ESR of capacitors.

The photo does not show which capacitor is being measured. Such readings are typical for ceramic capacitors. Here are the measurements on the firmwares of both authors.

[indman]

The photo does not show which capacitor is being measured.

The photo shows the measurement of an electrolytic capacitor 4.7uF(not ceramic). Is it really not clear that such a electrolytic capacitor of any company cannot have ESR = 0.11Ohm ?
Here are some more comparison photos for example. Transistor KП103 DSO-TC3 defines as a resistor.

[Fuzzy Star]

The photo shows the measurement of an electrolytic capacitor 4.7uF(not ceramic). Is it really not clear that such a capacitor of any company cannot have ESR = 0.11Ohm ?

I have some 10uF/16V Sanyo Os-con polymer electrolytics that measure ESR=0.11 Ohm
https://en.wikipedia.org/wiki/Polymer_capacitor

[indman]

Fuzzy Star,and the photographs that I provided do show polymer capacitors? Or does DSO-TC3 define them as polymer?

[Fuzzy Star]

Fuzzy Star,and the photographs that I provided do show polymer capacitors? Or does DSO-TC3 define them as polymer?

"electrolytic capacitor 4.7uF(not ceramic)... such a capacitor of any company"
Polymer capacitors are electrolytics, too and they don't look different. We can't be sure from your photo what type of electrolytic is it.

does DSO-TC3 define them as polymer?

Do these testers can detect and display capacitor type?

[indman]

Polymer capacitors are electrolytics, too and they don't look different. We can't be sure from your photo what type of electrolytic is it.

I assure you that the photo measured is an ordinary electrolytic capacitor, not a polymer one. If you can't tell the difference between an ordinary electrolyte and a polymer one, I'm sorry.

[oitar]

Ok, I bricked it, took a week
Maybe this will help someone avoid doing the same:
The Windows installation of WinAVR for some reason installs an empty folder for Programmers Notepad. So, used WinAVR Portable. Didn't [apparently] need to install the extra toolchain, but had to change the msys-1.0 file inside C:\WinAVR_Portable_V14_1\WinAVR-20100110\utils\bin to get everything to compile without errors.
The 1.44m firmware compiled fine with minimal set of features, the 1.48m was giving an error, so when I compared the 1.44 and 1.48 I saw both #define SPI_BITBANG, and #define SPI_HARDWARE were commented off. Enabling #define SPI_BITBANG made it compile without error..

That's when I decided to try SPI_HARDWARE, and also manually changed the low fuse from 0xff to 0xf7 using Avrdudess(I saw inside the Makefile: LFUSE_CRYSTAL = -U lfuse:w:0xf7:m, since I have a mega324pa, running 16 MHz external crystal)... //famous last words...

Whichever of the above did the trick, I cannot program anything on the cpu anymore, everytime avrdude "Detect" shows different device signature, and any attempt to change fuses or firmware gives an error. And of course the screen stays blank.
Any suggestions regarding resetting the fuses would be welcome , but it looks like- apart from cpu swap(which would be practically impossible, since i have no hot air station/experience), it's only good for the dust bin.

[madires]

You can debrick an ATmega324 by high-voltage (parallel) programming or maybe JTAG. Only a few ATmega programmers support the high-voltage mode, but some (many?) universal programmers do.

[ekoloski]

Fuse bits are dangerous...

It looks like that fuse config set the AVR to expect a low power crystal oscillator. If there's a crystal on there that just isn't being driven right, maybe you can rescue it by setting a slower bitrate and trying to program the fuse? With avrdude it's the -B option (substitute in your parameters for the programmer you're using, and experiment with the -B flag which is the bitclock period in uS): avrdude -p m324 -B20 ... -U lfuse:w:0xff:m

Otherwise as the previous poster mentioned, parallel programming is the way to recover it. The catch is that you'd need to remove the chip from the board first and you've stated that's a no go. Maybe there's someone local who can help out with the desoldering if necessary?

A number of programmers out there support hvpp. I personally use an older AVR Dragon, but some people even make their own programmers out of another AVR. If you are able to get it removed it would be something similar to:

avrdude -p m324 -P usb -c dragon_pp -U lfuse:w:0xff:m

[oitar]

Thanks for the replies! Why is it necessary to remove the chip for parallel programming? If I ensure all peripherals are disconnected, can't I do it in-circuit? I've already written it off, so wouldn't mind trying anything, if it will help others.
Sorry for wasting the time of one of the project creators !

[ekoloski]

I'd remove the chip out of caution, since I don't know what the schematic for this board looks like. HVPP uses 12 volts on the Reset line, if anything else on the board is connected to it and is not tolerant of 12V it could be damaged.

Beyond that, anything else connected to the pins could load it down and interfere with the programming. And lets not forget that there are a LOT of pins to connect (21 of them!) for parallel programming.

If there really isn't anything else on those pins that could get damaged or interfere, then you're right. The chip could be programmed in-place.

For reference, below is a snapshot from page 368 of the datasheet (this is a Mega324, right?) which shows the pins for parallel programming. Note that in addition to each named line all of PB is connected for data.

[Fuzzy Star]

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/