$20 LCR ESR Transistor checker project

[madires]

So, I rather invest some time on this unit than putting it aside or thowing it away. But to convert this schematic to the original one it's not feasible, as the changes are too many. Therefore if @madires and you and other readers can please support this new mod, I will appreciate it, and I think it will be of benefit for other "lucky" owners too.

All what we need might be just the pin assignment of the ATmega324 to configure the firmware accordingly.

[Feliciano]

I think you can simply ignore the STC of your TC1 variant, i.e. no need for the mod. Or remove it, as indman suggested.

Thanks for replying. I had that gut feeling: the mod could be simpler. However, do the m-firmware?:

the press of the button is detected by a low on pin 42, answered with a high on pin 16 to trigger the boosters.

(I meant at the boot time. Of course pin 42 should be also read for menu access, as pin 16 should be high during operation).

On the other hand, I'm checking this soldered display, and uses a different pin mapping (from right to left bottom-view):
1=GND, 2=Vcc, 3=PB4 (44), 4=PB3 (43), 5=PB5 (1), 6=PB7 (3)
Is that what you meant by:

All what we need might be just the pin assignment of the ATmega324 to configure the firmware accordingly.

So what do you think? Shall we forget the auxiliary PCB, remove the STC (for power consumption reduction), adjust the config, make, and flash? Or something else needs to be adjusted?

[carl1961]

It is running with the 8 hz crystal , I removed the 16 hz when I was having screen issues after I read in Karl-Heinz manual where he said something about , Logic Gate Chips on some of these boards and 16 hz not working on them, as this board has a no name china 20 pin Logic Gate Chip.

[indman]

carl1961, This is exactly the nuance I wanted to clarify with you.
The use of an additional microcontroller, which acts as a command translator for BGR displays as well as for the 8-bit paralell display that is installed in your clone version, does not allow full operation at a frequency of 16 MHz.
For whom this frequency factor is important, you should refrain from purchasing such GM328A models or find and connect a standard classic RGB SPI ST7735 display directly to the ATMega328 ports without an extra chip.
Somewhat earlier, one of the participants in the Russian-language forum identified the marking of this 20-pin chip - HC89S003A.
A similar controller 24-pin HC89F0531 can also be installed.

[carl1961]

carl1961, This is exactly the nuance I wanted to clarify with you.
The use of an additional microcontroller, which acts as a command translator for BGR displays as well as for the 8-bit paralell display that is installed in your clone version, does not allow full operation at a frequency of 16 MHz.
For whom this frequency factor is important, you should refrain from purchasing such GM328A models or find and connect a standard classic RGB SPI ST7735 display directly to the ATMega328 ports without an extra chip.

I bought this thing before I even knew about the firmware.
Thanks for the advice too, I will remove the ISP jig when I am done playing with this. I still trying to get the 1.51m to work, seems all the reason for not working is the 7735 driver.
Yes ,  now that you gave that chip number, it is more readable LOL in this photo of another similar model as mine.

[jdev99]

Just received this one, with original ATmega328P. They are still out there...

Many thanks for the link. It seems to be a version of the GM328A different from the ones showed in the comparison chart. Isn't "M328Kit+TFT(AY-AT)" a better choice?

I don't know if it is better, it does have firmware version 1.12k

[NF6X]

I am new to the transistor tester world, and I'm missing some context and history. Why is that additional STC microcontroller in there? Is that a feature of any of the OSHW designs, or something that the clone manufacturers added? I only see it connected to two ATMega pins in Feliciano's draft schematic. If it's not driving any other hardware, I don't understand why they spent money putting it on the board instead of implementing whatever it does in ATMega firmware. I saw indman's comment about it translating LCD commands, but I don't grok its reason for being there yet.

[indman]

NF6X, STC is an 8-pin power management controller that Chinese engineers have implemented in some clone models.
And the 20-pin(24-pin) microcontroller is another direction of Chinese engineering. They use crappy cheap BGR displays and connect them to ATMega that way. It's clear? In both cases, these Chinese tricks only worsen the design of the original author's project, which is optimally designed with a minimum number of parts used.

[NF6X]

I'm having a hard time wrapping my brain around the idea that they spent money on a whole microcontroller to manage the power button instead of implementing it in the main microcontroller firmware for free, given how profit-motivated I expect the clone manufacturers to be. Does it normally have additional connections not shown in Feliciano's draft schematic?

[indman]

NF6X, using STC involved adjusting the time (from 10 seconds to 25 seconds) until the device was completely powered off.
But this time can be easily configured in advance and in the author’s project. So I don’t see any justification for using an additional controller. Maybe someone else can explain it to you better?

[Feliciano]

The short STC story:
The STC15L104 on the older TC1 and variants is used as a timing/power MCU. On the older factory firmware there was a communication between it and the MCU in order to hold the 5V, and for how long. It had high standby consuption (IIRC it was the 3.3V unit overdriven @VBatt-Vd). Later the manufacturers updated it with a better model. Later the manufacturers removed as by the schematic indman shared recently (and also replaced the transformer with a second booster). You can refer to the pages around May 2018 for the whole STC&TC1 discussion/details. Here I attach the original schematic as reference.

And that's what's puzzling me with my different STC-based TC1:
At the first press of the button, 5V is generated and the MCU will power up, with a low on pin 42. It shall reply with an steady high on pin 16 for keeping the 5V. If another low comes on pin 42, it shall be processed as menu enter (if held low, IIRC), or reset (if quickly returned to high). As I said, I don't know what normally m-firware does with these pins, so I don't know whether it can be adjusted on the config, or it had to be a different subrutine, or it can be accomplished by an external circuit taking Vbatt and 5V (from different places), reading the low from the push button from Q2 transmitting it to PD1, and reading the high on PD2 and transmitting it to Q3. I'm waiting for confirmation on whether the additional workaround is not needed, else, which shall be the better approach.

[NF6X]

The best hypothesis I've come up with so far is "firmware engineer's uncle owns the local counterfeit STC factory, and snuck the part into the tester design for a kickback".

[indman]

NF6X, I, for example, it does not bother me in any way, and I will not and do not want to bother with hypotheses as to how and why details absolutely unnecessary for the project appeared. If you are so concerned about it, ask a Chinese engineer, such as FNIRSI, directly!

[Feliciano]

Agree. Please lets focus on the matter in question: how to make this work with OSHW firmware.

[indman]

Feliciano,you have checked the display connection and identified the controller pins. Are the rest of the peripherals connected in the standard way or are there also differences from the original circuit? There are a lot of unclear points on the schematic you showed earlier, the pins of the ATMega324 are not labeled. It would be nice if you could draw a more detailed circuit diagram.

[Feliciano]

Indeed:

I'm checking this soldered display, and uses a different pin mapping (from right to left bottom-view):
1=GND, 2=Vcc, 3=PB4 (44), 4=PB3 (43), 5=PB5 (1), 6=PB7 (3)

And not all the pins are labeled because I'm writing over an m328p schematic [WIP].

[indman]

That's understandable, that's not what I'm asking. To which ports are connected 6 measuring resistors, ION, calibration capacitor, IR detector?
This is all to be considered when customizing new firmware.

[2hry]

@Feliciano

Your tester looks like my JOYIT T7.
I have removed the Stc chip, and flashed m-firmware.
It is not working anymore, because the srv05 got damged, but i made some notes of the pinout.

LCD_RES          PB4           
LCD_DC           PB3
LCD_SCL          PB7
LCD_SDA          PB5
LCD_OFFSET_X     2               
LCD_OFFSET_Y     1               
LCD_FLIP_X                     

TP1              PA0
TP2              PA1
TP3              PA2
TP_ZENER         PA4
TP_REF           PA3
TP_BAT           PA5
TP_CAP           PA7

R_RL_1           PC0
R_RH_1           PC1
R_RL_2           PC2
R_RH_2           PC3
R_RL_3           PC4
R_RH_3           PC5

POWER_CTRL       PD7
TEST_BUTTON      PB2 
IR_DATA          PD3
ADJUST_RH        PC6

[indman]

I have removed the Stc chip, and flashed m-firmware.
It is not working anymore, because the srv05 got damged, but i made some notes of the pinout.

The tester can work without SRV05, unless, of course, the microcontroller is also damaged.
You could provide the firmware so Feliciano can test it on his clone.

[2hry]

I think the microcontroller is damaged.
It didnt start anymore and the srv05 got hot. So i removed it and the tvs, but it always measures a battery on pin2.

and compiled it in english again if anyone is interested.

[Feliciano]

Indeed 2hry firmware worked, and as madires suggested, without further hardware modifications. Thank you very much dears.

Now my unit is running 1.51m (STC no longer needed, removed). And with the hints on the pin assigments, I will work on the original configs for customization.

FWIW (maybe for the clones files), attached a comparison of some clones' PCBs (JOYIT, FNIRSI on the right).

PS: It also looks to me that 2hry's MCU is damaged.

[rddube]

Hello everyone,

Programmed my TT with version 1.51m and when I try to put it into L Monitor (inductance) it just stands on the screen in the photo and won't read anything and won't respond to the button press either.

What did I do wrong to not have it give my inductance readings?

Many thanks,

Raymond

[carl1961]

what version is this?

[rddube]

what version is this?

You mean the Ttester, it is version ST7565R .

[indman]

Programmed my TT with version 1.51m and when I try to put it into L Monitor (inductance) it just stands on the screen in the photo and won't read anything and won't respond to the button press either.

Enable the RLC Monitor mode in the firmware. Will the tester in this mode react to the connection of resistance, capacitance, inductance?

Feliciano, To which ports of the ATmega324 were pins 7 and 8 of the STC connected? I've almost updated the circuit diagram for FNIRSI's LCR-TC1.