Ensuring the safety of an Arduino-controlled H-bridge motor circuit involves monitoring current levels to prevent overheating and damage. One effective way to protect both MOSFET motor H-bridge and BJT motor H-bridge circuits is by implementing current sensing. By measuring the current drawn by the motor, an Arduino can trigger a stop command if the current exceeds safe levels, thereby protecting transistors, microcontrollers, and other components from failure.
A simple method to sense current in an H-bridge interfacing with Arduino is to measure the voltage drop across a power resistor in series with the motor and power supply.
Using Ohm’s law (V = IR), the current can be calculated, but this approach generates heat and wastes energy. To minimize power loss, a low-resistance shunt (0.01–1Ω) with a sufficient wattage rating is recommended. For example, with a 0.05Ω resistor and a voltage drop of 0.5V, the current flow is 10A, requiring a 5W-rated resistor to handle the dissipation safely.
A more efficient alternative for H-bridge motor circuit protection is a Hall-effect current sensor such as the ACS-712, which can measure up to 30A bidirectionally and provides an analog output for Arduino interfacing.
The following shows how one can use ACS712 sensor module with H-bridge motor drivers to measure the current and turn off the motor if threshold current is exceeded.
This method eliminates the heat dissipation issue associated with resistors and improves accuracy. In the guide current sensor ACS712 with Arduino tutorial, it is shown how to interface ACS712 with Arduino, how to read the voltage, find out the current drawn by the motors and display the current sensor value on the serial monitor. The following shows the circuit schematic.
Additional circuit protection measures include using a protection diode in H-bridge configurations to counteract back EMF, as well as incorporating capacitors to suppress electrical noise and smooth voltage fluctuations. SPDT mechanical relays, optocouplers, and different types of H-bridge drivers further enhance motor control safety and isolation, ensuring a reliable and robust Arduino-controlled robotics.
