This circuit is designed for indicating over-speed and direction of rotation of the motor used in mini hand tools, water pump motors, toys and other appliances. A 12V DC motor is coupled to the rotating part of the appliance with a suitable fixing arrangement. When the motor rotates, it develops a voltage. This over-speed indicator is built around operational amplifier CA3140. Set the reference voltage (depending on the desired speed) by adjusting preset at pin 2 of IC. When the voltage developed at pin 3 of IC is higher than the reference voltage at pin 2, output pin 6 of comparator IC goes high to sound buzzer and light up.
The rotation indicator circuit is built around AND gate 74LS08. Pin 2 of gate goes high when the motor rotates in forward direction, while pin 1 of gate is pulled high via resistor. When both pins 1 and 2 are high, output pin 3 of gate goes high to light up LED.