View Full Version : Measuring Actual voltave from ADC

02-17-2009, 01:30 AM
Hi guys,

I am working with ARM7 LPC2138, and doing the ADC module.
I loaded an example ADC program and it is giving values from 0 to 1016 through serial port. Using Multimeter i found that the max voltage is 3.19 volts.
Could anyone help me decoding the value in the register to find the actual voltage the ADC is measuring?

Here are few voltages i have measured:
Register Value Volts
0 0
80 0.25
120 0.38
256 0.81
1016 3.19

02-17-2009, 09:11 AM
Whats the reference voltage of ADC ?
I think the adc is set in 10bit resolution.

[(+Vref)-(-Vref)]*ADC REGISTER
Vin = ------------------------------------------ + (-Vref)
(2^N) - 1

Where N= ADC resolution

+Vref= Vcc
-Vref= 0v (GND)

02-17-2009, 09:15 AM
In ur case

+Vref=3.3 Volts

- Vref= 0v