ADC voltage reference?

luartos
Posts: 16
Joined: Wed Nov 23, 2016 7:17 pm

ADC voltage reference?

Postby luartos » Sat Dec 10, 2016 3:16 am

It seems that ADC voltage reference is about 1.1 volts. This is right?.

Using new api functions adc1_config_width / adc1_config_channel_atten / adc1_get_voltage, an input value arround 1.1 volts gives raw values near 4095 using a resolution of 12 bits.

Any one has information about this?

WiFive
Posts: 2624
Joined: Tue Dec 01, 2015 7:35 am

Re: ADC voltage reference?

Postby WiFive » Sun Dec 11, 2016 9:56 am

Seems approx 1.1v but would like to have temperature and Vdd compensation data.

onehorse
Posts: 70
Joined: Mon Feb 15, 2016 1:35 am

Re: ADC voltage reference?

Postby onehorse » Sun Dec 11, 2016 7:55 pm

Strange, on my board 4095 corresponds to 3V3.

WiFive
Posts: 2624
Joined: Tue Dec 01, 2015 7:35 am

Re: ADC voltage reference?

Postby WiFive » Sun Dec 11, 2016 9:51 pm

onehorse wrote:Strange, on my board 4095 corresponds to 3V3.
Well anything above 1.1v is 4095 @ 0db. Did you test with lower voltage?

onehorse
Posts: 70
Joined: Mon Feb 15, 2016 1:35 am

Re: ADC voltage reference?

Postby onehorse » Sun Dec 11, 2016 10:05 pm

Yes, I have pin 34 connected to a voltage divider as a LiPo battery moinitor and I could track the battery while charging. I have the resistors not quite right, they are 20K/100K meaning that at 4.2 V the voltage into the ADC is 3.5 V so yes anythibng avive about 4 V into the voltage divider will show up as 4095. But with a partially drained battery I can see the voltage climb from 3 V on up while charging.

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