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Inductive Relay Output


The Relay

A relay can be thought of as an electrically/magnetically operated switch.

Relays contain a primary coil of wire to generate a magnetic field. This makes and breaks (by magnetism) the contacts of a switch within the relay. This relay has a Double Pole Double Throw (DPDT) switch which allows two different circuits to be switched or controlled independently.

Higher powered circuits can be independently controlled with a relay.

Circuit Notes:

The 33 ohm resistor reduces the supply voltage down to 6 volts.
The diode prevents dangerous back emf (voltage), generated by the relay, from reaching the previous process module (usually a transistor/buffer stage).


Motor Reversing

 

The output of this DPDT relay has been connected so it can reverse or flip the voltage going to a motor. When the relay input receives a "sinking" input voltage from the transistor, it operates and switches its electrical contacts. This causes the power connected to the motor (via the relay) to reverse its polarity (ie. the + and - swap round). The motor now changes its direction of rotation.

The inductive (back e.m.f.) effects are quite strong and the diode is again used to remove them (see inductive outputs).