display 0-12v battery voltage on LCD

[hhhsssmmm]

hello guys

i just want to know the math equations that will be needed to go into my C18 code to display the battery voltage from 0-12V on LCD.

Of course the battery voltage is scaled from 0-5 volts and im using a 10bit adc on PIC18F2420 with VDD as the ref.

MY head has worked out following to put in my C code for the necessary scaling factor conversion.

1 / [(R1+R2)/R2] .... lets say this inverse results of value X

ADC voltage at PIC pin (0- 5V) = X * ADRES .... lets say this product results of value Y.

Now Y is the actual voltage from 0 to 5V on the ADC pin. This of course represents the scaled 0 - 12V via the potential divider.

Now what is the next step after this to get the value of Y to represent the value from 0 - 12V for the battery voltage so i can display
on LCD??

what must i multiply or divide to get my desired result?....

im lost...plz help

Thanks

Haseeb

 

[MikeMl]

Voltage = (VDD*ADCreading)/(VoltageDividerRatio*1024) where:

1. VoltageDividerRatio = 5/12 = R2/(R1+R2) or whatever your voltage divider resistors are. Note that the source impedance looking back at the voltage divider from the ADC input should be ≤ 10KΩ, and that the AC source impedance should be lowered by bypassing the tap on the voltage divider to VSS with ~1uF capacitor.

2. VDD is the actual PIC supply voltage, to three significant figures.

3. 0≤ADCreading≤1023