Saturday, June 14, 2014

Wheatstone bridge application using ATmega16A

Abstract: In this project we are going to build a circuit that calculates the unknown resistance in a Wheatstone bridge using voltage subtractor and Internal ADC of a ATmega16A.

Wheatstone bridge is used to calculate the unknown resistance in a circuit. Here we are using OpAmp based subtractor circuit to calculate the voltage 'Vg', which is used to calculate the unknown resistance. The two buffer amplifiers are used to provide virtual isolation between the wheatstone bridge and the subtractor. Below circuit shows the working of a subtractor,

NOTE: In case of ATmega16A we don't need to use external subtractor because ATmega16A is having differential input mode.

Here we selected external ADC reference voltage 5V. So, the output of a ADC value is multiplied with its resolution to get input voltage, 5/1024. This voltage is given as 'Vg' in wheatstone bridge equation to calculate the resistance, remaining three resistors are set to 1k ohm.

Here's the program flow

  to download the code

Working images of the total circuit

Click here to see the working video.