ADC ports stability!


I made some measurements on my APM board togethet with a 3DR power module and an atto 90A board.
Both sensors gives a stable sense voltage to the APM board but the reading out on MP is allways oscillating between 16.5 and 16.7V (multimeter is reading a perfect 16.6V). So I checked the shematics of the APM board and saw that the analog reference voltage supply pin (AVCC) was directly connected to VCC ! When I check the recommendations of Atmel about AVCC they ask to use an LPF between VCC and AVCC (just a 10mH inductance with a 100nF capacitor). You can imagine now my question, Why is this LPF not implemented ? My two cents are that if the reference voltage is not stable then the ADC’s can’t do their job’s on an accurate manner. What do you think about this ?


I’ve had a chat with one of the 3dr people who is familiar with this and it sounds like you’re right. Now the question is whether it will ever be fixed…my guess is that the APM2.x series won’t receive much focus now that the Pixhawk is available.

Hi, thanks for your reply. I think also that APM dev is stopped because of lack of space and performance in favour of Pixhawk. I checked the shematics of the Pixhawk and the filtering seems to be done correctly, should be interesting to have some feedback from someone that has already one :wink:

I’m tempted also to go over to Pixhawk (32 bit/168Mhz v. 8bit/16Mhz) :slight_smile: