_{1}and R

_{2}, the other from R

_{3}and R

_{4}. The voltage at the point between R

_{1}and R

_{2}, and that between R

_{3}and R

_{4}will vary according to the resistor value. V

_{bridge}is the voltage between these points, as shown in the diagram below:

When the voltages are equal V

_{bridge}will be zero, at which point the bridge is said to be balanced. At this point the value of R

_{4}can be found from:

R

_{4}= (R

_{3}* R

_{2}) / R

_{1}

A typical application for a Wheatstone Bridge is for measuring resistance; if R

_{1}is variable and is adjusted it until V

_{bridge}= 0 the value of R

_{4}can then be found from the above equation.

If all four resistor values (R

_{1}to R

_{4}) and the supply voltage (V) are known the voltage across the bridge (V

_{bridge}) can be found by working out the voltage from each potential divider and subtracting one from the other. The equation for this is:

V

_{bridge}= (R

_{4}/ (R

_{3}+ R

_{4}) * V) - (R

_{2}/ (R

_{1}+ R

_{2}) * V)

This can be simplified to:

V

_{bridge}= ((R

_{4}/ (R

_{3}+ R

_{4})) - (R

_{2}/ (R

_{1}+ R

_{2}))) * V

If the bridge is balanced the equivalent resistance of the circuit between V and GND is:

R

_{1}+ R

_{2}in parallel with R

_{3}+ R

_{4}

R

_{E}= ((R

_{1}+ R

_{2}) * (R

_{3}+ R

_{4})) / (R

_{1}+ R

_{2}+ R

_{3}+ R

_{4})