Adding Decimal Point

[markscotford]

Thanks Melanie, you are a star worked first time, love you to bits.

[markscotford]

Would like to add some sort of Auto calibration to the system if possible, to iron out any variation is resistor tolerances across different PCB boards. The PIC I am using has some on-chip EEPROM memory. I was thinking of something on the lines of, at first power up, as part of the manufacturing process, the board is connected to a known set voltage (lets say 90.0 volts for example) and the firmware calculates the required divison/multiplication to get the display to read bang on 90.0 Volts. Any suggestions would be very appreciated.

Mark in Spain.

[Melanie]

That's quite simple... say on power-up a Button is held for 5 Seconds... the LCD Displays...

"Adjust for 90v"
"And Press SET"

When the Button is pressed, the ADC WORD value (containing the 90.0v reading) is then saved as a HighBYTE and LowBYTE component into two seperate EEPROM locations (since each EEPROM location can only save a BYTE).

When you power-up normally, rather than jumping into the Calibration routine (described above), your program instead loads the CAL value from EEPROM, and you would use the CAL value in your math with a modified routine, rather than the 1023 value routine previously exampled earlier in this thread...

0.1% Resistors are probably cheaper than paying the Labour to run through a CAL routine at manufacture. One of your divider Resistors could instead be a multi-turn high-stab precision POT (so you could also Calibrate for 90.0v using that method instead).