A Design of DC Motor Controller


This DC Motor Controller circuit will control a 12V dc motor. The system will have three pushbuttons: a START button, a REVERSE button and a STOP button. Initially, the motor must not be running. When the START button is pressed, the motor will run in one direction. Pressing the REVERSE button (while the motor is running in START direction) must have no effect on the motor. Pressing the STOP button must stop the motor from running.

Pressing the REVERSE button while the motor is stopped will make the motor run in a direction (opposite to the direction for the START button). Pressing the START button (while the motor is running in REVERSE direction) must have no effect on the motor. Pressing the STOP button must stop the motor from running.


The circuit design has two parts: a logic control part and an amplifier part. The logic control part consists of logic gates, pushbuttons and a voltage source of 5V. For the pushbuttons, S1 is the START pushbutton, S2 is the STOP pushbutton, and S3 is the REVERSE pushbutton. These pushbuttons act as grounding buttons, and the inputs from the voltage source are passed through inverting buffers before going through the actual
logic gates. The logic gates basically implement the above conditions given the inputs from the pushbuttons. The output from the logic control is a positive voltage for START, a negative voltage for REVERSE and zero voltage for STOP.

The amplifier part uses two op-amps and two transistors (PNP and NPN). The op-amps amplify the output (positive or negative) voltage from the logic control to around 12V. The current output from the op-amps, however, fail to drive the 12V dc motor, so the transistor part is present in the circuit. The transistors basically amplify the current to a level enough to drive the motor.


1 2N6121 transistor (NPN)
1 2N6124 transistor (PNP)
1 74LS00 (buffer)
1 74LS04 (AND)
1 74LS11 (OR)
1 74LS32 (inverters)
3 7k resistors
2 10k resistors
2 30k resistors
3 normally open pushbuttons
1 12V dc motor

Schematic Diagram

Click HERE To view the schematic diagram of the dc motor controller circuit.

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