OLED meter up to DC500v....S.O.S.

[capwizard]

bought A 7-in-1 Electrical Parameter Power Voltage Meter, Can anyone help me modified to Voltage Range DC 500v, for my Poorman LED tester project, how can i modified the firmware after I put a resistor network? Maybe just modify the decimal point.

PS: ST's 8-bit microcontroller: 16 MHz STM8S 8-bit MCU, 8 Kbyte Flash, 128 byte data
EEPROM, 10-bit ADC, 3 timers, UART, SPI, I²C

https://cdn.badcaps-static.com/pdfs/...5c7935d788.pdf

PS: the last PIC, those pins, highly suspect, manufacture used for Data read and write.

Specifications:
Color: Black
Display: 0.96" OLED Blue Digits
Voltage Measurement Range: DC 0.00-33.00V (+/-)0.3%+2dgt
Current Measurement Range: DC 0.000-3.000A (+/-)0.8%+3dgt
Time Measurement Range: 0-99h 59min
Power Measurement Range: 0-99.00W
Temperature Measurement Range: -15°C-60°C
Capacity Measurement Range: 0-99.999Ah
Energy Measurement Range: 0-999.99Wh
Item Size: 47 * 28 * 21mm / 1.85 * 1.1 * 0.83in (L * W * H)
Item Weight: 18g / 0.65oz
Package Size: 5 * 5 * 4cm / 1.97 * 1.97 * 1.57in (L * W * H)
Package Weight: 27g / 0.96oz

[mariushm]

Re: OLED meter up to DC500v....S.O.S.

The voltage comes in and then you have those two resistors R1 and R2 , which form a voltage/potential divider.

R1 = 1003= 100 followed by 3 zeroes = 100 000 ohm ,
R2 = 1002 = 100 followed by 2 zeroes = 10 000 ohm

and the output goes to the ADC pin on the microcontroller.

So Vadc = [ R2 / (R1+R2) ] * Vin = 10k / 110k * Vin = 1/11 Vin
So when you have the maximum of 33v on the input, you have 3v on the ADC pin

The microcontroller looks like it's ST STM8S003F3 : https://cdn.badcaps-static.com/pdfs/...aefcff0d12.pdf

It has a 10 bit ADC but no internal voltage reference, so it uses the input voltage as voltage reference. In this particular example, the LDO is probably a 3.3v one, so this may explain why it caps the input voltage on the ADC to 3v

Anyway, the idea is that you can play with the resistors so that you'll get 3v on the ADC pin for a higher input voltage. Without reprogramming the firmware inside (which would be difficult), the easiest would be for example to say 33v when you have 330v on the input, or 3.3v when you have 33v and so on. It's an easy multiply by 10.
If you really want to, maybe you could get it to show 33v when you have 660v at the input but you'd still have to do math every time you read the voltage.

It's unlikely you'll get it to say 50v or anything more than 33v since it's programmed internally to not show more than 33v.

So to show 33v at 330v , you'd need R2 10kohm and R1 = 1.09 megaohm but you may get too little current for the ADC to work right if you use megaohm resistors.

Probably safer to go with something like 4.7 kohm and 512.3 kOhm (510k and 511k are easy to find, just add a 2.3 or 1.3k resistor in series to get )
Easy... instead of 1/11 you try to get a 1/110.

If you want to try to find other combinations, download Electronics Assistant and it has a Potential Divider Calculator... all you need to remember is that the gadget is programmed to show 33v for 3v on the ADC input pin.

ANyway... seems like a waste of time and effort when you can just buy a cheapo 830b multimeter or some uni-t meter and repurpose it.
They're like 3$ on eBay : http://www.ebay.com/itm/DT830B-LCD-D...5l-ew6WWDevH4Q

[capwizard]

Re: OLED meter up to DC500v....S.O.S.

Thank you for your fast response i really appreciate it.

I try to show of this new OLED technology and put it on my Poorman's TV LED screen tester.

PS: I follow your instruction found OLED 100V DC Voltmeter, maybe use this, modify to 1000v, the Poorman's TV LED screen tester voltage range up to DC 440v. Thank you.