0
\$\begingroup\$

The default for the Arduino A/D capability is a 5v reference. Given the 10-bit A/D converter, this is 4.88mV per number from 0 to 1023. The Arduino also supports setting the analog reference voltage to 1.1V, giving an accuracy approximately 5 times higher.

I wanted to try increasing that further. The Arduino has an internal 32k ohm resistor on AREF, so I connected a 1M ohm resistor to Vcc. The voltage reads 0.16V, but then A/D converter doesn't work. Presumably there is a lower limit. With 100k, it works, but the reference voltage is more than 1.1V, so there isn't much point.

Is it possible to set the reference voltage to less?

\$\endgroup\$
  • \$\begingroup\$ It's much better to get an instrumentation amplifier and use it to increase the voltage to the 5V range, if you're trying to detect a very small voltage. \$\endgroup\$ – pjc50 Oct 29 '12 at 11:36
  • \$\begingroup\$ Accuracy is a strange word to chose for the effect of decreasing the AREF. \$\endgroup\$ – Cybergibbons Nov 27 '12 at 6:44
1
\$\begingroup\$

Not sure which Arduino you have but on page 377 the datasheet for the atmega2560 says Vref min for the adc is 1.0V. So unfortunately that probably won't help you.

\$\endgroup\$
0
\$\begingroup\$

analogReference(type) EXTERNAL

Aref can be 0 to 5V but needs to be low impedance source and noise free.

Can you ensure the noise on Aref, signal and analog ground is < 1mV ?

The Uno is already obsolete and the Due has a 12bit ADC. The more resolution you have, the greater attention is required to EMI, conducted and radiated noise on signals, ground and Aref.

Consider boosting the signal.

\$\endgroup\$
  • 1
    \$\begingroup\$ The Uno is obsolete? \$\endgroup\$ – Cybergibbons Nov 27 '12 at 6:44

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.