ADC Math - reading 30Vdc

[jmgelba]

I tried the DIG command earlier and I got an odd character.

Interestingly, with a 8.0V source, I'm getting a reading of 15.4V. I'll have to do some further testing.


Meanwhile, any good Math for a thermistor?

[jmgelba]

I tried the DIG command earlier and I got an odd character.

Interestingly, with a 8.0V source, I'm getting a reading of 15.4V. I'll have to do some further testing.


Meanwhile, any good Math for a thermistor?

Fixed both of these issues. Thanks for the help everyone.
On to the next part of the project: controlling a digital pot.

[Charles Linquis]

Also make certain that you have an adequate acquisition time. The ADC is most accurate when the source impedance is < 2K ohms. With a 10 K source, you will need an acquisition time of 11uSec or greater.

[jmgelba]

Thanks Charles. I have had this set to 50uS right from the start. All my ADC channels are working very well.

[aajgss]

How accurate do you need you 3V? A 100K and 10 K don't make a 10:1 ratio.
Ohms Law RTotal/ Rx (in this case 10K)
110K / 10K is a ratio of 11:1

So dropping 30V across 110K will give 27.27V across the 100K and 2.73V across the 10K


aajgss