$20 LCR ESR Transistor checker project

[UKTech]

Hi all
I've been lurking now for quite sometime but thought I'd better register into this forum and thank everyone for all the knowledge that I've gained and a special thanks to madires and KH for all the support that is given to us all. What a fantastic forum subject we've got. I now have two of these little mighty meters and just ordered the third, an AY-AT clone with the colour screen and the rotary encoder, so will be updating as soon as it arrives on the slow boat. The last one was a TC4 and the other is one of the early ones that I've just put into the old test gear box.
I'm an old timer but enjoyed electronics way back when I was conciderably younger and transistors were the thing, but at least I saw the first i.c.'s come in, what fun were those 555 things. I decided that when I retired I'd pick this hobby up again and also have a play with 3DPrinting, well I've played quite well with the Tevo Black Widow 3DPrinter and I've had built a nice shed for the electronics, I've spent quite sometime with the Arduino, so now to play.
I can honestly say that I've just finished reading all 195 pages and will rescan to pick up the parts that I've tagged that are of special interest to me.
Sorry to have taken up so much of the page but just had to say.......
Thanks again to everyone.

[Azure]

The k and m firmware won't run on an unmodified TC-1 because of the additional MCU U4. But it's possible to replace U4 with a small circuit which I've posted on this page. Also I've run into problems with the TC-1's power supply, it's not stable. The "Clones" file is in the m-firmware's tgz archive and lists settings for a few clones and some hints. And here's the wiring of the LCD for your diagram:

PB7 (SCK)  - LCD SCK
PB6 (MISO) - LCD SDA
PB5 (MOSI) - LCD A0
PB4             - LCD /RESET

If the designer of the clone would have payed more attention to the pin assignment the TC-1 would be able to use the hardware SPI for driving the LCD.

I agree it is annoying that they don't publish their changes to the code or schematic.  Given that there are a lot of these units out there, which will most likely end up faulty and people want to get them going or upgrade them with newer features functions: Isn't it possible to modify the "m" version code to support the configuration utilising U4.  I am happy to try and give the changes a go.  I have a working TC1 with original 324 chip I can use to check things (take measurements) and also as a reference. I have another one I am trying to modify which now has a blank 644 in place.

For reference the 2 PCB's appear to be almost the same.  Only differences I have spotted are (as per my schematic in previous post) C11 now has a second Cap C12 in parallel and any higher numbered Caps have been renumbered by +1 (C12-C23 become C13-C24).  EN pad had been moved from the edge to near the middle.  D2 is physically smaller.  All of the other traces and vias and components on the PCB appear to be placed and route exactly the same.  I will draw an updated diagram and post if it anyone wants it.  I can also take a picture of the 2 different but similar PCB's and post those if people are interested.

I do want to get my second unit with the 644 working with more of the new code features eventually, also very keen to try and contribute in any way I can to help others.  I have adequate test gear for the task (lab bench supplies, 4ch digital and analogue scopes, 5 1/2 digit mm, basic signal generator, simple logic analyzers, tools for surface and PTH rework, AVR JTAGICE3...).

I am new to the source repository and find this thread very useful but still not sure which repository version to download as a starting point for converting a TC1 with ATMEGA 324.  I downloaded ComponentTest 1.33m and it does not have an archive folder, so I must have the wrong file.

[perieanuo]

Download all from start page


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[madires]

Maybe it's an idea that someone actually can make a summary, make a new topic and make that as a sticky?
I have the idea that a few people here know exactly what's going on and what/where to find everything.
But to me it's also a huge maze to go through.

jakeisprobably started working on a FAQ/how-to a while ago but I don't know the current status.

[madires]

I can honestly say that I've just finished reading all 195 pages and will rescan to pick up the parts that I've tagged that are of special interest to me.

Wow! I hope it wasn't too boring

[madires]

Isn't it possible to modify the "m" version code to support the configuration utilising U4.

Unfortunately U4 doesn't simply simulate a button press or read the power-on signal, it uses a serial protocol to communicate with the ATmega.

I will draw an updated diagram and post if it anyone wants it.  I can also take a picture of the 2 different but similar PCB's and post those if people are interested.

I'm sure some users would be interested in your diagram and the pictures.

I am new to the source repository and find this thread very useful but still not sure which repository version to download as a starting point for converting a TC1 with ATMEGA 324.  I downloaded ComponentTest 1.33m and it does not have an archive folder, so I must have the wrong file.

The "Clones" file is part of the ComponentTester-1.33m.tgz archive.

[b_force]

Maybe it's an idea that someone actually can make a summary, make a new topic and make that as a sticky?
I have the idea that a few people here know exactly what's going on and what/where to find everything.
But to me it's also a huge maze to go through.

jakeisprobably started working on a FAQ/how-to a while ago but I don't know the current status.

Just a post were people van even find the links for downloads and the global differences?
At this moment people need to read through a whole bunch of pages to discover that the firmware can even be changed.

[timelessbeing]

At this moment people need to read through a whole bunch of pages to discover that the firmware can even be changed.

Everybody who says this clearly didn't try. It's on the first page

[Azure]

OK, I have just finished a marathon post read of all 196 pages.  I did skim read but was trying to focus on the progress of the various hardware/software versions not specific faults.

I have hopefully read all the TC1 posts.  Seems several have been down this road before me.  I would prefer to not have to change U4 for now and try to see if we can understand it.

My plan is to try and do the following (for TC1 style):
Verify what the supply voltages are like on a working unmodified unit (using scope and 5 1/2 digit DMM measurements);
Update my schematic with more info as provided by previous posts;
Make the previously suggested mods to my second unit (now sporting a 644) 0.1% test resistors, replace 78L05 vreg and/or TL431 vref chips;
Make improvements to 5v rail on second unit as previuosly suggested by Madires;
Look at any variations on U4 signals (long press/short/double press) from previous waveforms posted;
Try and decode the power on protocol between U4 and U1.

Hope that might help to confirm this clones strange behaviour and make it a working part of the clone configs info.  Please let me know if any of it is useful or just a waste of time.

If there is anything else needed I have missed regarding the TC1 that I can possibly do please let me know.

[Azure]

I am trying to work out what is available as a replacement part to improve the 5v regulation on the TC1 from the 78L05 SOT-89 they use.

Would anyone with knowledge of the tolerance requirements cast your eyes over the attached specs of a couple of pin compatible SOT-89 LDO's with better line and load regulation I have found?

Below are links to the data sheets, could not attach them (not for lack of trying, they were over the size limit allowed):
Element14, LD2981 http://www.farnell.com/datasheets/2310115.pdf?_ga=2.139301427.1894826597.1530201477-1167880404.1500891526
Mouser/Digikey AP7381 https://au.mouser.com/datasheet/2/115/AP7381-1220674.pdf

If these look suitable I will order the one from Element14 first and see how they perform.

[perieanuo]

I am trying to work out what is available as a replacement part to improve the 5v regulation on the TC1 from the 78L05 SOT-89 they use.

Would anyone with knowledge of the tolerance requirements cast your eyes over the attached specs of a couple of pin compatible SOT-89 LDO's with better line and load regulation I have found?

Below are links to the data sheets, could not attach them (not for lack of trying, they were over the size limit allowed):
Element14, LD2981 http://www.farnell.com/datasheets/2310115.pdf?_ga=2.139301427.1894826597.1530201477-1167880404.1500891526
Mouser/Digikey AP7381 https://au.mouser.com/datasheet/2/115/AP7381-1220674.pdf

If these look suitable I will order the one from Element14 first and see how they perform.

You don't need ldo you need precision regulators I guess.


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[Azure]

You don't need ldo you need precision regulators I guess.

Most precision vregs are around +-2% which is not as good as the ones suggested like MCP1702.  The ones I suggested are better precision and can be soldered directly in place of the TC1's 78L05, the MCP1702 like most others have different pinouts are not a direct replacement.

[perieanuo]

pinout is not really the point.you have tons of precision regs and you find easy some place to adapt. the realy issue is in fact temperature drift... I remember lt1461 series as example

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[madires]

Some thoughts about selecting a voltage regulator for the Transistor Tester:
- It should handle 100mA (MCU) plus whatever is needed for display and hardware options.
  The MCU does need much less in average but a few checks use high currents very briefly.
- It should be able to handle rapid load changes (sleep mode, normal operation, high current checks, hardware options).
- It should have a good regulation to keep the voltage stable under changing loads.
- It doesn't need to be one with a low output voltage tolerance but such a regulator would improve the tester's accuracy.

We recommend the MCP1702 (250mA, 0.4%, about EUR 0.60). Affordable and much better than a LM78L05 plus TL431.

This brings us to the external voltage reference. The purpose of the reference is to determine Vcc and therefore it should have a tolerance at least one order of magnitude better than the voltage regulator's tolerance. A TL431 is ok for a 78L05, a LM4040 would be better. If you use a MCP1702 you don't need a reference at all unless you're a voltage nut .

I hope this helps with the selection of the voltage regulator and external voltage reference.

[perieanuo]

I don't agree,microchip says in datasheet Vout could be bttween 5V -3% and 5V+3% for MCP1702.No way 0.4%.
And I saw this often confirmed in real life.
That's why I proposed the LT.just as example.
Regards,ovidiu


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[UKTech]

madires   "Wow! I hope it wasn't too boring"

To be honest it has been a good read, it's always good to read, and a day without learning is a day wasted, that's how I see it.

[pierreraymondrondelle]

read again, the folowing is an abstract of the Microchip MCP1702 datasheet:

"The MCP1702 is capable of delivering 250 mA with
only 625 mV (typical) of input to output voltage
differential (VOUT = 2.8V). The output voltage tolerance
of the MCP1702 is typically ±0.4% at +25°C and ±3%
maximum over the operating junction temperature
range of -40°C to +125°C. Line regulation is ±0.1%
typical at +25°C".
Do you really use electronic circuits at home and operate your tester over this range ?
EDIT:
reading further, @25°C, min and max Output Voltage tolerance remains within +-2% !

[b_force]

At this moment people need to read through a whole bunch of pages to discover that the firmware can even be changed.

Everybody who says this clearly didn't try. It's on the first page

I think it's more clearly that the amount of information is overwhelming.

[perieanuo]

read again, the folowing is an abstract of the Microchip MCP1702 datasheet:

"The MCP1702 is capable of delivering 250 mA with
only 625 mV (typical) of input to output voltage
differential (VOUT = 2.8V). The output voltage tolerance
of the MCP1702 is typically ±0.4% at +25°C and ±3%
maximum over the operating junction temperature
range of -40°C to +125°C. Line regulation is ±0.1%
typical at +25°C".
Do you really use electronic circuits at home and operate your tester over this range ?
EDIT:
reading further, @25°C, min and max Output Voltage tolerance remains within +-2% !

Have your even seen a pro calculating regarding 'typically' values?
If anyone bother to change something in this meter should not regard for 2 euros cheaper but in components with slow drift and higher precision, in fact I do so.
And second I prefer leave microchip power products to begginers, they never give satisfaction.have you seen lot of microchip power stuff in laptops for example?have you wondered why they use LT or others?
You can recomend what you consider,as I do based on my own experience.
And 'it's pin to pin compatible' also I don't even consider for a 3 pin device, I just find a place for the replacement.
Mods is for advertised people, who can switch pin 2 with pin 3 if necessary.
I'll never reply to this kind of post,it's not professional, just ego stuff.
Ovidiu


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[CNC Engineer]

I saw the TC-1 but also a TC-6 and a TC-7.
Does anyone know the differences?

Thanks, CNC Engineer.

[indman]

CNC Engineer,these devices imeet very similar functionality and differ only in the display which is used. LCR-TC1, LCR-TC7-colored display. LCR-TC6 - the monochrome display.

[timelessbeing]

At this moment people need to read through a whole bunch of pages to discover that the firmware can even be changed.

Everybody who says this clearly didn't try. It's on the first page

I think it's more clearly that the amount of information is overwhelming.

 

[Cliff Matthews]

Food for thought.. I was thinking about an alternate "headless" technician version of the AVR tester:

Why not send display data via USB serial protocol and have an easy to read screen app on the host that stores all the graphics (to free-up AVR memory allowing an on-board 5v-to-??v boost convertor to run tests at higher voltages and higher current?

But then again, maybe it's been done? Maybe there's also a USB OTG version? 

[madires]

The next m-firmware version will have a VT100 display driver (incl. color support) which outputs everything via a TTL serial interface. Only the fancy symbols are missing.

[Cliff Matthews]

So it's conceivable a variant could send simplistic raw data, symbol number and pin order then?

IMHO, ditching display for USB OTG (w/ DC-DC step-up) and Android app would make this more usable in 3rd world countries
 (9v cells cost precious $ and many basic tech's have a cell-phone but no PC)

* Without symbols precious AVR memory could run PWM step-up supply voltage (but I really don't know if it's feasible..)