Whenever you buy a new Servo motor and you connect it to the circuit, and if it doesn’t rotate, you might think that Servo may be faulty. So each time when you face this kind of problem, you think of testing it somehow. So here we are building a circuit to test the Servo motor, using 555 timer IC, where you can rotate it in forward direction or reverse direction by pushing the Buttons. If it rotates accordingly, means Servo is in good condition. Before going into the circuit, we need to know about How Servo works.
Step 1: How Servo Motor Works
Servo motors are very useful in electronics and embedded systems. You can find the use of Servo motor everywhere around you, they are used in toys, robots, CD tray of computer, cars, aeroplane etc. The reason of this wide scope is that, servo motor is very reliable and precise. We can rotate it to any particular angle. They are available in wide range, form high torque motor to low torque motors.
Servo motor works on PWM (Pulse width modulation) principle, means its angle of rotation is controlled by the duration of applied pulse to its Control PIN. Basically servo motor is made up of DC motor which is controlled by a variable resistor (potentiometer) and some gears. High speed force of DC motor is converted into torque by Gears. We know that WORK= FORCE X DISTANCE, in DC motor Force is less and distance (speed) is high and in Servo, force is High and distance is less. Potentiometer is connected to the output shaft of the Servo, to calculate the angle and stop the DC motor on required angle.
Servo motor can be rotated from 0 to 180 degree, but it can go up to 210 degree, depending on the manufacturing. This degree of rotation can be controlled by applying the Electrical Pulse of proper width, to its Control pin. Servo checks the pulse in every 20 milliseconds. Pulse of 1 ms (1 millisecond) width can rotate servo to 0 degree, 1.5ms can rotate to 90 degree (neutral position) and 2 ms pulse can rotate it to 180 degree.
Step 2: Servo Motor Tester Circuit
We know that 555 IC can generate pulse of any width and any frequency (Learn more about 555 timer IC here), so it can also be used to drive Servo by generating a pulse of proper width. So here in our circuit we used 555 timer in Astable mode by connecting resistors between PIN 8 & PIN 7, PIN 6 & PIN 7, and a capacitor between Ground and PIN 6. This circuit will generate the pulse to rotate Servo motor in Forward and Reverse direction, by pressing button 1 and button 2 respectively. When button 1 is pressed Resistor R2 of 10k ohm is used and when button 2 is pressed Resistor R3 of 68k ohm is used.
Remember that value of Resistors and capacitors have been chosen very carefully to generate a Servo driver pulse, so use the components exactly of same value as shown in circuit diagram. And also use proper power source according to your servo motor, otherwise servo will not rotate.