dc42:
void startConversion()
{
ADMUX = (B01000000 | currentAdcChannel); // Vcc reference, select current channel
delayMicroseconds(5); // only needed if using sensors with source resistance > 10K
ADCSRA = B11001111; // ADC enable, ADC start, manual trigger mode, ADC interrupt enable, prescaler = 128
}
...
BTW using a delay inside an isr should generally be avoided, however very short delays to allow hardware to settle are OK.
I'm trying to understand what the delay will do to the ADC process, but my understanding of the manual isn't great. I've reread the manual on ADC several times but I cannot make sense of statements such as:
An analog source applied to ADCn is subjected to the pin capacitance and input leakage of that pin, regardless of whether that channel is selected as input for the ADC. When the channel is selected, the source must drive the S/H capacitor through the series resistance (combined resistance in the input path).
Does this imply that the ADC circuit starts charging once a channel is selected in ADMUX but before the ADCSRA ADSC bit is set? Elsewhere the manual states that the sample & hold of a channel only starts after the ADSC bit in ADCSRA is set, so a delay before setting ADCSRA shouldn't affect the charging of the ADC cap?