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Electronics => Electronics => Topic started by: webgeek on January 15, 2010, 10:39:39 PM

Title: Axon 2 ADC Max Voltage
Post by: webgeek on January 15, 2010, 10:39:39 PM

Really stupid question but I don't see the answer anywhere (I'm likely just missing it). What's the max voltage one of the ADC pins can take as input on the Axon 2? I'd like to have a basic software voltage monitor to watch my LiPos that power the motors on my mech. Since the batteries are not used for logic, it's perfectly reasonable for the Axon to be able to disable the use of motors before the voltage drops too low. Probably something right around 9.5v or such. I'd like to be able to monitor 11.1v directly (without a voltage divider if I can). Is this possible? Thanks!

Mike

Title: Re: Axon 2 ADC Max Voltage
Post by: SmAsH on January 15, 2010, 10:51:15 PM

Well, if it was me i definitely wouldn't be putting anything near 9v5 near my adc!
To be safe things should be kept near 5v so i doubt the axons adc could do this.
Have you considered using an external battery monitor circuit to measure and output an analogue value to the axon?

Title: Re: Axon 2 ADC Max Voltage
Post by: rgcustodio on January 16, 2010, 12:00:13 AM

This information should be in the datasheet of the AVR used.
Typically (ie most AVRs and other MCUs) AVCC (voltage for the ADC subsystem) and AREF (analog reference voltage for the ADC) should be equal to VCC.

Title: Re: Axon 2 ADC Max Voltage
Post by: Admin on January 16, 2010, 04:37:07 AM

Well, anything above 5V would result in negative current, frying the ADC pin (and maybe more).

If you want a battery monitor, you'll need a voltage divider consisting of two resistors to make it ADC safe:
http://www.societyofrobots.com/schematics_batterymonitor.shtml (http://www.societyofrobots.com/schematics_batterymonitor.shtml)