What does it do?
|The motor subsystem provides rotational motion when powered.
How does it operate?
Basic motor circuit
Click on the circuit diagram to download a Livewire file of the circuit that you can investigate and add to your own circuit.
The motor turns when the signal coming into the driver is high.
Low cost electrical motors generate electrical noise that can interfere with the ‘processing’ ICs. The 220nF polyester capacitor is added to reduce this noise. In extreme cases, an opto-isolator can be used to remove noise.
The reverse biased diode is included because, when motors are switched off, they can generate a ‘back e.m.f.’ that can damage the driver. When the motor is switched off the diode conducts current and prevents the damage.
Solar motors are less noisy and more efficient, but they are more expensive.
Motors come in a variety of sizes, voltages and currents. The power supply for the motor (which can be separate from the supply for the rest of the electronics) must provide the voltage needed by the motor.
The driver providing the input signal must be able to provide a current considerably larger than the specified current for the motor because there is a ‘surge’ current when the motor first starts, or if it ‘stalls’. A safety margin of ´5 is recommended.
Relay circuit for reversing a motor
The simple circuit shown above is suitable for switching a motor on and off.
It is possible to reverse the direction of rotation of a motor using a double-pole double-throw relay, as shown on the left, or a L293D driver IC.
- Causing movement. Using mechanisms, the rotational movement from the motor can be converted to linear or reciprocating movement.
Normally a motor would not be mounted on the PCB. Usually a terminal block is mounted on the PCB and wires from this are connected to the motor.
The direction of rotation of the motor is reversed if the terminal connections are reversed.
A PCB-mounting terminal
Small electrical motors rotate at high speed. It is usually necessary to use them with a speed-reducing gearbox.
Build and test the unit that will provide the driving input signal before adding the motor.
Make sure that the motor turns when power is applied from the driver unit.
If there is a fault, check the motor by removing it from the circuit and applying power to it directly. Check the voltage at the terminals of the terminal block.
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