Here is an example of level-switching - my implemention of an autoselect 2 / 10v voltmeter on the Arduino:
long readV(int inPort)
/*
* Returns Volts at inPort in milliVolts
* Aref must be set to "INTERNAL" for these conversions to work!
* Warning: The 5v aref may not be accurate with USB!
* (c) 2009 qs@quantsuff.com
*/
{
long V ;
/* Take reading from ext Meter and divide with the ADC reading,
* then mult the previous # to get new adjustment.
* 1M in series acts as V-divider
* Parallel 150k to gnd to get 9.5v fs */
float ref9V5adjust = 9.22983; // Start: 9.319;
float ref2V2adjust = 2.121742; //Cal'd against known good meter
digitalWrite(13,HIGH) ; // 10v scale first
delay(10);
V= analogRead(inPin); // 0-1023 on 2v2 scale
V= (analogRead(inPin) * ref9V5adjust) + .5 ;
digitalWrite(13,LOW);
if (V<2200) {
delay(10);
V= analogRead(inPin) ;
V= (analogRead(inPin) * ref2V2adjust) + .5 ; // ignore prev readings
}
return(V);
This is the output as the Arduino monitored its own voltages (Aref and 3.3).
