$20 LCR ESR Transistor checker project

[oitar]

So, 324 out, 644 in, plenty memory available for more features The issues with the bandgap reference(reported last year) are all gone- so the 324 was defective to start with. Looks like the Auto-adjustment is quite sensitive, and gives error if the probes are not plugged really tight.
Next- rotary encoder, low-tolerance resistors and external voltage reference.

Quick question: I've noticed the zener measurement goes progressively(and proportionally) off- from spot-on at 0.5 V to about 2 V over the actual voltage at 25 V. The Auto-adjustment doesn't fix it(even when completed successfully). Is there a way I can tweak it manually?

[madires]

The TC-1/T7 uses just a resistor (10k) to limit the current for the Zener check, i.e. the test current will decrease as the Zener's V_Z increases, and vice versa. The Zener voltage will vary with the changing test current, especially with a too low current. A better solution would be to use a constant current source (as in the ATmega644 circuit in Karl-Heinz' dccumentaion).

[Feliciano]

FYI: To be added to the list of non-supported clones, I've just spotted an STC '51-based DIP40 unit, with a text-based (1602) display.

[hapless]

Doesn't look like a clone. Looks like a dedicated L/C meter. Does the display claim that it's anything else?

[indman]

FYI: To be added to the list of non-supported clones, I've just spotted an STC '51-based DIP40 unit, with a text-based (1602) display.

This is an DIY F/L/C meter and is not relevant to this project.
https://www.aliexpress.com/item/3256806396807109.html?_randl_currency=USD&_randl_shipto=US&src=google

[Feliciano]

Reading at the screen of the sample picture, yes, you're right, but the banggood title says "Transistor Tester Resistance Capacitance Meter Tester Digital Frequency Meter Multi-function Measurement Electronic DIY Kit ". So, another misleading seller.

[wesk18]

running firmware ComponentTester-1.41m, is it possible to add the autobots logo or any other logo to the fish8840-tft?

[madires]

No, but you could modify the firmware to add that feature. The most simple way would be to utilize LCD_Symbol() and split the logo into tiles (same size as the symbols).

[LeWidget]

Hey all,

Picked up a tester, LCD-T7, it was $14.50aud so I thought why not, though it's a bit different than what I've seen. The chip seems to be unmarked so I assuming it's non-authentic? The battery is also built in rechargeable & doesn't use a 9v like others.

Can I do anything with it? Unfortunately it doesn't have the pads for testing Surface-mount components, unless there's a way to test in the slots.

Also, can anyone explain the 123|1232? How is this used to test?

[Kim Christensen]

1,2, & 3 are the test points. All the ones are connected/grouped together. As are the twos. As are the threes. It just allows you to insert parts with different lead spacing easier.
Be aware that the K & A will output around 30V and are for testing zener diodes only.

Don't put a capacitor into K & A and then immediately stick it into 1,2,3 because that'll destroy the tester. Always make sure capacitors are fully discharged before testing them.

[LeWidget]

1,2, & 3 are the test points. All the ones are connected/grouped together. As are the twos. As are the threes. It just allows you to insert parts with different lead spacing easier.
Be aware that the K & A will output around 30V and are for testing zener diodes only.

Thanks Kim, much appreciated

So, when testing, I don't do 1+1, I have to do 1+2, 1+3, 2+3, 1+2+3?

What does the K & A mean?

Don't put a capacitor into K & A and then immediately stick it into 1,2,3 because that'll destroy the tester. Always make sure capacitors are fully discharged before testing them.

Ouch, thanks for the heads up lol. I think I did that with an LED earlier  , lucky it wasn't the capacitor.

Any idea why they would include 1x capacitor, 1x LED, 3x (what appears to be) wire terminals?(see attached pic)

[Kim Christensen]

I have to do 1+2, 1+3, 2+3, 1+2+3?

Yes.

What does the K & A mean?

Cathode and Anode.

Any idea why they would include 1x capacitor, 1x LED, 3x (what appears to be) wire terminals?(see attached pic)

The 3-wire terminals (Actually crimp pins) are for calibration. If you insert them, as is, into 1,2&3 and press "start" then the unit will go into self calibration mode.
Not sure if the Chinese firmware also will ask for a capacitor during self calibration. Usually you use a better quality film capacitor than the one they gave you.

The LED is just a bonus part for checking the tester. It'll flicker as it gets tested.

[LeWidget]

The 3-wire terminals (Actually crimp pins) are for calibration. If you insert them, as is, into 1,2&3 and press "start" then the unit will go into self calibration mode.
Not sure if the Chinese firmware also will ask for a capacitor during self calibration. Usually you use a better quality film capacitor than the one they gave you.

Thanks again Kim

I ran a test, seemed to come back ok (see pic). Didn't ask for a cap though.

[oitar]

Brag time

1. Original Atmega324(slightly defective) replaced with Atmega644.
2. The power management ic replaced with the 2 transistor hack(see attached, yeah looks like a dog's breakfast, but it works nicely; will put a bit of hot glue over).
3. Button replaced with rotary encoder- helps prevent arthritis from multiple button presses
4. Don't think I'll even replace the probe resistors- I'm happy with the precision already.

Changing the zener testing to separate terminals- away from the zif socket should be done as a matter of necessity, sooner or later one will forget either a charged cap, or  the probes in the wrong zif pins, and toast the cpu.

Cheers to all, thanks @madires for still keeping the upgrades going, and answering even the dumbest questions!

[BennehBoy]

I've just come to use my T7 after quite a period of none use and found that the screen repeatedly cycles between full white and off whilst trying to charge the unit.

I'm assuming that it's been killed at some point - maybe even the last time I used it...

I've not read all 380 pages (eeek!), and a quick google did not turn up a similar symptom, but any ideas?

I'm hoping it's just a case of reflashing something/doing the transistor mod on the STC15L104W.

Thanks

[Calambres]

I also have an AY-AT with genuine DIL ATMEGA328 chip that suddenly and randomly started to write some crap characters on the screen.
Quite annoying if you ask 

[madires]

I've just come to use my T7 after quite a period of none use and found that the screen repeatedly cycles between full white and off whilst trying to charge the unit.

Please check the voltage of the LiPo battery. It's possibly very low (deeply discharged). If charging doesn't help try a new battery.

[BennehBoy]

I've just come to use my T7 after quite a period of none use and found that the screen repeatedly cycles between full white and off whilst trying to charge the unit.

Please check the voltage of the LiPo battery. It's possibly very low (deeply discharged). If charging doesn't help try a new battery.

It was very low - 0.1v when I checked it just before the time of my last post.  It's been sat trying to charge since then, will check it shortly.

UPDATE - no change to the voltage, I guess it's toast?

[Yuriy_K]

For those who see similar readings on silicon transistors on the k-firmware, which is incorrect (upper left corner). This is not a program error, but an incorrect measurement scheme. If we add inductance and capacitance to the scheme, highlighted in red SMD, we get correct readings for silicon transistors. For germanium transistors, measurements are shown - lower right corner.

[madires]

UPDATE - no change to the voltage, I guess it's toast?

Yep, the LiPo battery needs to be replaced. I'd recommend also to add a small switch to the battery (to prevent draining it by the high quiescent current).

[madires]

For those who see similar readings on silicon transistors on the k-firmware, which is incorrect (upper left corner). This is not a program error, but an incorrect measurement scheme. If we add inductance and capacitance to the scheme, highlighted in red SMD, we get correct readings for silicon transistors. For germanium transistors, measurements are shown - lower right corner.

Also recommended by the ATmega's datasheet, i.e. a small inductor plus cap for the ADC's power supply.

[indman]

For those who see similar readings on silicon transistors on the k-firmware, which is incorrect (upper left corner). This is not a program error, but an incorrect measurement scheme. If we add inductance and capacitance to the scheme, highlighted in red SMD, we get correct readings for silicon transistors. For germanium transistors, measurements are shown - lower right corner.

Also recommended by the ATmega's datasheet, i.e. a small inductor plus cap for the ADC's power supply.

Here is a reply from Karl-Heinz Kübbeler on the advisability of using a inductance(throttle-coil) in the AVCC power supply circuit:
"There is no need to use a throttle (coil) for the AVCC supply.
During the ADC period no digital activity disturb the VCC power supply.
Any inductance in the AVCC supply also have a resistance.
The influence of the resistance of the coil probably interfere the
measurement result more then a remaining noise at the VCC power.
The enhancement of ADC resolution requires a noisy or unstable signal.
The mean value of several input values is always the input value itself,
if there is no change of the value. Only if the input signal changes a
little bit, the mean value can interpolate the steps of the ADC by
a statistically effect. For example the mean value of
10, 11, 11, 12, 11, 10, 11, 10, 11, 11 is 10.8 ! "

[madires]

There's no simple answer. It depends on how well the power supply circuitry is designed. Some Vcc ripple helps (is necessary) with the ADC (averaging multiple readings). But a sudden larger load change will cause a short drop/rise of Vcc. With a marginal power supply and no inductor for AVCC the ADC's 5V reference voltage would change too. The LC filter reduces that change of AVCC. For a proper power supply the LC filter isn't really needed (might even be counterproductive). But for a poor one it can be a good idea. And the values of the LC filter should be choosen to suppress ripple to some extend while keeping enough noise for the ADC. This is also one of the reasons why some clones deliver results which are a bit off.

[indman]

But for a poor one it can be a good idea.

It is a good idea for poor and rich people to make a quality power supply for this device that is not afraid that a sudden change in load will cause Vcc to drop/rise, thus eliminating unnecessary parts in the form of external REFs, coils, i.e. crutches for the lame.

[BennehBoy]

Yep, the LiPo battery needs to be replaced. I'd recommend also to add a small switch to the battery (to prevent draining it by the high quiescent current).

I've ordered a larger capacity lipo (that will fit the case) and will certainly be adding a switch, thanks.