Potential Divider

A potential divider circuit consists of two components put in series across a voltage source.  They divide the voltage into smaller parts.

In the diagram two resistors are in series across a battery.  They divide the 9 volts of the battery so that the output voltage is smaller.  Here, because the resistors have the same value, they divide the voltage in half.  If you use different resistors, or variable resistors, you can get exactly the output voltage you want.  This is very important in electronics

The formula for finding the output voltage is quite simple.  Because the current is the same through both resistors, using Ohms Law, we can say:

Vout        =              Vin            or      Vout   =     Vin x Rbotto  

Rbottom      (Rtop + Rbottom)                       (Rtop + Rbottom)

You can either remember the formula or use ratios for the calculations.  Potential divider circuits can be used with all kinds of sensors for the input to a system.

Example:  In the circuit arrangement shown above, if Rtop is 100k and Rbottom is 50k and Vin is 9v, what is Vout?  Since Rtop is 2 x Rbottom, we have to split the 9v of Vin 2:1.  6v across Rtop and 3v across Rbottom works out fine.

Or…                             Vout   =      9v x 50k     =  9x1/3 = 3v

                                                      (100k + 50k)

You can use resistors, variable resistors, potentiometers, light dependent resistors (LDR), thermistors, microphones, infra red sensors, touch sensors, water and moisture sensors and switches of all kinds in a potential divider circuit.  The potential divider circuit will form the input for all sorts of processes and outputs.