$20 LCR ESR Transistor checker project

[oitar]

That's interesting! The delay should happen only once when switching from Vcc to band-gap. Increasing the delay would increase the time of the voltage measurement by the same delay. In the Zener check the voltage is measured several times. Hence the maximum delay should be: number of calls of ReadU() * delay. Have you tested that with the original code or your modfied ReadU()?

With the original code. If I use the modified one, the reading is correct regardless of time.
When original code is used with various wait functions, it is definitely taking that long as mentioned.

To make your changes work you need also to change the default voltage reference, which is done here:

Code: [Select]

  /* prepare bitfield for register: start with AVcc as voltage reference */
  Channel &= ADC_CHAN_MASK;        /* filter reg bits for MUX channel */
  Channel |= ADC_REF_VCC;          /* add bits for voltage reference: AVcc */


You got me here
As soon as I change the code you specify to: Channel |= ADC_REF_BANDGAP;, the wrong reading comes back- even with my modification still in place!

So you start with Vcc and set Vcc again when Value >= 1024 (your mod), i.e. the band-gap reference isn't used at all. And since the measurements are fine with just the Vcc reference the actual problem is related to the band-gap reference.

I'm afraid I cannot argue with that. For voltages between 3 and 24 V, the error is around 1.5%. Under 3 V it gets a lot worse: -3% at 2.0V, -5% at 1.5V, -9% at 1.0 V, and -18% at 0.5 V

Let's try something else. Take the original ReadU() and change

Code: [Select]

      if ((uint16_t)Value < 1024)       /* < 1V (5V / 5 samples) */
to

Code: [Select]

      if ((uint16_t)Value < 900)
The idea is to check if the voltage of the band-gap reference might by a bit too low.

Result:
Votage Input, V:     Reads as, V:
       10.5               10.66
       10.0               10.13
        9.5                 9.622
        9.0                 9.090
        8.5                 8.586
        8.0                 2.165
        7.5                 2.025
        7.0                 1.885
        6.5                 1.754
        6.0                 1.614
        5.5                 1.474
                  .........

[indman]

oitar,your board has a QFN44 form factor controller. Have you checked the reliability of the soldering of its contacts with a multimeter? The thought that there is a bad contact or not enough connection with GND does not leave me.There have been cases when soldering all the contacts of the processor fixed the problems.

[oitar]

oitar,your board has a QFN44 form factor controller. Have you checked the reliability of the soldering of its contacts with a multimeter? The thought that there is a bad contact or not enough connection with GND does not leave me.There have been cases when soldering all the contacts of the processor fixed the problems.

Visually all solder points look ok. All GND pins of the chip read properly. I will try and re-solder all pins later.

Just for interest's sake, if the internal bandgap reference cannot be used(for whatever reason), can I swap it with the 2.5V external? This would give a better precision for voltages below ~2.5V. After a few attempts to modify the ADC.c code, I keep getting "timeout" errors.

[Sudya]

Comparison of LCR-TC2 testers.
The firmware for the converted (LGT8F328) to ATMega328P is added to the folder with the sources.
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[madires]

Result:
Votage Input, V:     Reads as, V:
        8.5                 8.586
        8.0                 2.165

Seems to follow the lower threshold for switching to the band-gap reference. There are some measurements which use the band-gap reference directly. Do you also get strange values for ESR and inductance?

[madires]

Just for interest's sake, if the internal bandgap reference cannot be used(for whatever reason), can I swap it with the 2.5V external? This would give a better precision for voltages below ~2.5V. After a few attempts to modify the ADC.c code, I keep getting "timeout" errors.

As soon as you use an external voltage reference at AREF you can't use the internal ones anymore, i.e. neither Vcc nor band-gap.

[oitar]

Seems to follow the lower threshold for switching to the band-gap reference. There are some measurements which use the band-gap reference directly. Do you also get strange values for ESR and inductance?

Definitely when measuring resistance. Don't have proper samples(with known parameters) regarding ESR or inductance.

[oitar]

As soon as you use an external voltage reference at AREF you can't use the internal ones anymore, i.e. neither Vcc nor band-gap.

I was hoping it's possible to just make the program use the voltage from the external source, but consider it the bandgap voltage, without re-wiring.
Sorry this is just my ignorance talking, I'm still learning the internals of an AVR.

[elecdonia]

Just adding another data point on the LCR-TC2 to this thread. Old version vs new version, both bought from "Z industry store" on Aliex about 18 months apart.
   Old version:
      Generic case (with modification)
      f/w v2.3E
      PCB T7-PLUS v1
      Atmel marked 44 pin MCU

MCU very likely to be Atmel ATmega324.  Why do I think this is so?
   1) No Chinese MCU comes in 44-pin package (yet)
   2) 6-pin header near top edge of PC board is standard Atmel ISP programming interface. Chinese MCU don't use ISP. It is unique to Atmel

Some modification of existing -K or -M firmware may be necessary, but it certainly is feasible to replace the Chinese firmware because this MCU is actually mega324. Also possible to upgrade MCU to mega644 or mega1284.

New version:
Customized case based on original generic case
f/w v3.1E
PCB T7-PLUS v2.0
Unmarked 32 pin MCU

MCU likely to be LGT8F328P
Several people on this forum report successfully replacing LGT8F328P with Atmel ATmega328P. Hardware mod is simple because only a few pins have different functions. However existing -K or -M firmware needs modification for mega328P to work with this PC board. When time permits I plan to try this myself.   

[Yuriy_K]

Using symbols_32x39_hf.h. For the correct display of contact numbers, you need to correct the line:
PIN_LEFT | PIN_BOTTOM, PIN_RIGHT | PIN_TOP, PIN_RIGHT | PIN_BOTTOM, /* UJT n-type */

[Calambres]

I've just received a T7-H multi-function tester (V1.1 E) and it seems there is no way to perform the auto calibration, neither with the supplied 3 pin header nor by shorting the also supplied three DuPont cables with mini grabbers.

Is this the normal behaviour of this version? The calibration instructions supplied in the AliExpress page are for the T7... Is it different in this T7-H model?

[madires]

Very likely a tester with an alternative MCU.

Some hints on identifying the MCU:
- MCU in DIP is usually an genuine ATmega.
- APT32F172K8T6 has different power pins:
  - 32-LQFP/QFN: 18=Vss, 19=Vdd (ATmega328 32-TQFP: 5=Gnd, 4=Vcc)
- APT32F172K8T6 uses SWD port for ISP:
  - 5 pins: Vdd, Vcc, F_SDAT, F_SCLK, F_RST
- Testers with APT32F172K8T6 often lack a quartz crystal.
- LGT8F328 has slightly different pins:
  - QFP32L: 21=PE2/SWD (ATmega328 32-TQFP: 21=Gnd)
- LGT8F328 uses SWD port for ISP:
  - 5 pins: Gnd, Vcc, SWD, SWC, Reset
- Clone variants with an genuine ATmega are usually about EUR/US$ 5 more
  expensive than the variant with a different MCU.

[Calambres]

MCU is unlabeled, 8 pins per side so no Atmel   

This one has a XTAL, albeit a very small one (X2) just by the pads for the bigger non existent X1.



Some more photos below, includig two showing the process of not performing the calibration as indicated in the instructions.


Comparing the readings with both a DER EE-5000 and a Peak Atlas DCA55, the values are all over the place 

[madires]

5-pin ISP header (SWD), one pin connected to MCU's pin 21 -> LGT8F328

[Calambres]

Thanks a lot. I suppose there's nothing I can do with this tester other than asking AliExpress for a refund 

[indman]

I suppose there's nothing I can do with this tester other than asking AliExpress for a refund 

Right! It is necessary to return such a low-quality product back to the seller and demand a refund of the money spent.

[Calambres]

I'm afraid the return postage cost to China is greater than the cost of the item itself 

[Calambres]

This chinese seller is really wicked 

I sent him a message through the AliExpress messaging service explaining my concerns about the impossibility to perform a calibration with this tester. On next day the seller answered, in a very amicable way, to send him a video showing the problem. Everything OK so far so I did a couple of videos, one using the supplied 3 pin header and another shorting the also supplied three DuPont cables with mini grabbers. I uploaded both of them to my youtube channel.

So far so good... except for one little detail: AliExpress does not allow neither sending files through their messaging system nor even sending youtube links. As soon as the system detects a youtube link or even the word "youtube", the message is zapped and a menacing warning is produced:

Note: This message contains prohibited content and hasn't been sent. Any further messages of this nature may result in account restrictions.

Isn't it wicked? 

Of course the seller is perfectly aware of this AliExpress behaviour and asks for a video just to make all things difficult 

I've sent a note to the seller explaining what happened (without using the evil "youtube" word). Let's see what the seller comes with now 

Meanwhile, if you feel courious and want to take a look at those two aforementioned videos:

[Calambres]

Ah, by the way, anyone knows what is hFEr?

[indman]

Ah, by the way, anyone knows what is hFEr?

hFEr=REVERSE_HFE
"All transistors have inverse Hfe, since you can always swap the collector and emitter. This is equivalent (but not strictly identical - Hfe is a large signal, BF is a small signal hybrid signal) to the SPICE BR parameter, just as BF is equivalent to Hfe."

Link: https://www.physicsforums.com/threads/what-is-reverse-hfe.305553/

[Calambres]

Thanks, mate!   

[4thDoctorWhoFan]

I did not realize these testers had a selftest/cal mode. lol
I tried it on my T7H and it worked.  I guess I have older firmware as mine says v1.1 (No E after the 1.1 like yours in the pictures)

Perhaps it's just a firmware issue and not a hardware problem.

[madires]

The self-adjustment feature is simply missing in the modified firmware for that specific alternative MCU. Either it's the lack of flash memory or the manufacturer is unable to adapt the self-adjustment to the other MCU. Because ATmegas are quite expensive at the moment some clone manufacturers switched to other MCU types. And those testers are a disaster, mostly thanks to a poorly ported firmware.

BTW, TC-1 and similar clones run a modified k-firmware (fancy graphics, less features).

[Calambres]

Then which is the best option today? 

[indman]

Then which is the best option today? 

M328Kit+TFT RGB(GM328A) ATMega328 Dip form factor. It is easy to make an adapter for this clone for ATMega644.
This is the best option for today, so as not to get a fake and wasted money, nerves and time!