$20 LCR ESR Transistor checker project

[madires]

Some AY-AT/GM328A come with a different LCD emulating an ST7735 (semi-compatible). That LCD module has an MCU and a level shifter on the PCB. In this case use LCD_SEMI_ST7735 (see 'Clones' file).

[Embehu]

Some AY-AT/GM328A come with a different LCD emulating an ST7735 (semi-compatible). That LCD module has an MCU and a level shifter on the PCB. In this case use LCD_SEMI_ST7735 (see 'Clones' file).

Thank you so much, I flashed the new firmware, it runs into the Probing.... and then restart again and again. And the screen direction is flipping, X become Y. So what am I still doing wrong?
here is my 7735 semi that I found somewhere on internet

Code: [Select]


#define LCD_SEMI_ST7735
#define LCD_GRAPHIC                     /* graphic display */
#define LCD_COLOR                       /* color display */
#define LCD_SPI                         /* SPI interface */
#define LCD_PORT         PORTD          /* port data register */
#define LCD_DDR          DDRD           /* port data direction register */
#define LCD_RES          PD0            /* port pin used for /RESX */
#define LCD_CS           PD5            /* port pin used for /CSX (optional) */
#define LCD_DC           PD1            /* port pin used for D/CX */
#define LCD_SCL          PD2            /* port pin used for SCL */
#define LCD_SDA          PD3            /* port pin used for SDA */
#define LCD_DOTS_X       160            /* number of horizontal dots */
#define LCD_DOTS_Y       128            /* number of vertical dots */
#define LCD_LATE_ON                     /* turn on LCD after clearing it */
#define FONT_8X8_HF                     /* 8x8 font */
#define SYMBOLS_30X32_HF                /* 30x32 symbols */
#define SPI_BITBANG                     /* bit-bang SPI */
#define SPI_PORT         LCD_PORT       /* SPI port data register */
#define SPI_DDR          LCD_DDR        /* SPI port data direction register */
#define SPI_SCK          LCD_SCL        /* port pin used for SCK */
#define SPI_MOSI         LCD_SDA        /* port pin used for MOSI */



[madires]

Does the probing cycle start again or does the tester restart (showing the firmware version)?

[Embehu]

Does the probing cycle start again or does the tester restart (showing the firmware version)?

It restarts. Showing firmware version 1.46 then Battery ok, Probing... and the screen light up then get dark and start showing firmware again...

[indman]

Embehu,Try this firmware to test the performance of your clone. ignore the russian language.
Will there be the same reboot effect as on your 1.46m?

[Embehu]

Embehu,Try this firmware to test the performance of your clone. ignore the russian language.
Will there be the same reboot effect as on your 1.46m?

Oh my God, suprisingly it works, screen also ok. But the results is not good (I think because I'm using 2,234V as Vref). 

[indman]

Embehu,for what purpose did you apply such a Vref? Put a good quality LDO +5v and remove the external REF altogether!
Attach the zip archive to a message with your config.h and config_328.h. I will compile the 1.46m firmware for you in English.

[Embehu]

Embehu,for what purpose did you apply such a Vref? Put a good quality LDO +5v and remove the external REF altogether!
Attach the zip archive to a message with your config.h and config_328.h. I will compile the 1.46m firmware for you in English.

I got LM399 (it has 6.75 super stable Vout) from scratch then I use three 470K resistors 0.1% in series then I got 2234V. I think it will be better than mpc1720 or tl431
You are so kind to me but if I can I would love to make it myself because if I change the function I don’t really want to bother you again. Otherwise  I will send you via inbox.
Really thank you for helping me!

[indman]

I got LM399 (it has 6.75 super stable Vout) from scratch then I use three 470K resistors 0.1% in series then I got 2234V. I think it will be better than mpc1720 or tl431

Put original MCP1702-5002 - it will be enough for this clone and you will get great results without using ExtVref. LM399 can be used in other project, where high stability of the reference voltage is required.

[madires]

Yep, LM399 is total overkill.

[Embehu]

Put original MCP1702-5002 - it will be enough for this clone and you will get great results without using ExtVref. LM399 can be used in other project, where high stability of the reference voltage is required.

Yep, LM399 is total overkill.

Ah ha, I got it. So this project requires stability of 5V more than Vref.
Since I really get difficulty while buying the real mcp1702. How about the one from China? Do you have any idea about it?

[indman]

Since I really get difficulty while buying the real mcp1702. How about the one from China? Do you have any idea about it?

In 99% of cases you will receive a fake or relabeled part from China. You can take a risk and order it from a seller who has the highest number of orders of this LDO and positive feedback from buyers - shop FU NENG Store
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjt9a2qqev4AhVJKewKHYq1AFM4ChAWegQICRAB&url=https%3A%2F%2Fwww.aliexpress.com%2Fw%2Fwholesale-mcp1702.html&usg=AOvVaw0n34iQzC8z5oOlhG0OeJ6J
But I'm not at all sure it'll be an original part.

[Embehu]

In 99% of cases you will receive a fake or relabeled part from China. You can take a risk and order it from a seller who has the highest number of orders of this LDO and positive feedback from buyers - shop FU NENG Store
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjt9a2qqev4AhVJKewKHYq1AFM4ChAWegQICRAB&url=https%3A%2F%2Fwww.aliexpress.com%2Fw%2Fwholesale-mcp1702.html&usg=AOvVaw0n34iQzC8z5oOlhG0OeJ6J
But I'm not at all sure it'll be an original part.

Absolutely I know it then I would rely on the Vref function with lm399. In Vietnam it’s super hard to order just a mcp1702 from digikey or mouser because the price would be really high. Anw I will figure it out!

[Feliciano]

Put original MCP1702-5002 - it will be enough for this clone and you will get great results without using ExtVref. LM399 can be used in other project, where high stability of the reference voltage is required.

Yep, LM399 is total overkill.

Ah ha, I got it. So this project requires stability of 5V more than Vref.
Since I really get difficulty while buying the real mcp1702. [...]

AFAIK the ATmega generates its internal Vref from an amplified bandgap (obviously feeded from Vcc), therefore if the Vcc is stable enough, so is the Internal Vref. Else, we use the external Vref.

I got LM399 (it has 6.75 super stable Vout) from scratch then I use three 470K resistors 0.1% in series then I got 2234V. I think it will be better than mpc1720 or tl431

You can either modify the source code to work with a non-standard External Vref, or you can create an arrange to obtain the one we normally use. Several examples of such arrangements can be found on the Appendix C of the AN42 of LT.

[madires]

In Vietnam it’s super hard to order just a mcp1702 from digikey or mouser because the price would be really high. Anw I will figure it out!

You can also use any other 5V regulator with a stable output (measure the voltage and update UREF_VCC in config.h).

[madires]

AFAIK the ATmega generates its internal Vref from an amplified bandgap (obviously feeded from Vcc), therefore if the Vcc is stable enough, so is the Internal Vref. Else, we use the external Vref.

The internal bandgap reference (1.1V) can vary between 1.0 and 1.2V. The Transistortester:
- assumes Vcc is 5V exactly
- can check for an external 2.5V reference and use it to update the actual Vcc
- measures the internal bandgap reference with Vcc as reference

[Embehu]

My thinking is quite simple, the tester uses 2.5V as ref so I change to 2.234 then the mcu will use “new value” to calculate everything. So I’m wrong right?

[madires]

In that case you'll also need to change the voltage range check in CheckVoltageRefs() in main.c:

Code: [Select]

  /* check for valid voltage range */
  if ((U_Ref > 2250) && (U_Ref < 2750))      /* voltage is fine */

Try 2000 for the lower threshold and 2500 for the upper.

[lusant]

Hi,

I know there are a lot of different models, anyway have you saw this one ?
What is the purpose of USB interface ?

I try to use it to supply the module, it shows around 7 V, but didn't measure a simple resistor.

[LinuxHata]

Is there a version of firmware for these devices, which skips battery tests and other welcome messages on each button press?
This is very annoying.....

[Per Hansson]

Hi,

I know there are a lot of different models, anyway have you saw this one ?
What is the purpose of USB interface ?

I try to use it to supply the module, it shows around 7 V, but didn't measure a simple resistor.

I have no idea what version that is, but trying a OCR translation it seems to be saying that the USB port is only for user upgrades (of the firmware) and that it does not supply power.

[madires]

I know there are a lot of different models, anyway have you saw this one ?
What is the purpose of USB interface ?

No, but it looks similar to the LCR-T4, just with an additional USB to serial adapter (CH340). So the USB interface could be for TTL serial (both OSHW firmwares support a serial interface) or for ISP (programming the ATmega).

[madires]

I have no idea what version that is, but trying a OCR translation it seems to be saying that the USB port is only for user upgrades (of the firmware) and that it does not supply power.

Then it should be possible to update the firmware directly via avrdude.

[madires]

Is there a version of firmware for these devices, which skips battery tests and other welcome messages on each button press?
This is very annoying.....

Let me guess, you're still running the modified firmware which came with the clone? Which clone do you have?

[indman]

I know there are a lot of different models, anyway have you saw this one ?

A very strange implementation of the circuitry on this clone. The quartz resonator is not used, but the 7th and 8th pins of the processor are connected to an empty 6-pin connector. Instead of ExtVref, LM358 is included. Another K2 button appeared on the board