Single Pole Double Throw (SPDT) – This type of a relay has a
total of five terminals. Out f these two are the coil terminals. A common
terminal is also included which connects to either of two others.
The
output of each PIC pin is 5V with max output current of 20mA or 0V with 0mA
output. The voltage is not enough to run high power device e.g. motor,
solenoid. Thus we need a relay to control these high power items. A simple
switching circuit (using NPN transistor, C9013) will be used to energize /
de-energize the input coil of the relay.
The relay output is single pole
double throw (SPDT). And its coil can be energized using 5V and de-energized
using 0V. Normally the relay output NC and COM will be connected. When the
input coil of relay is energized, output NO and COM will connect. The switching
can be used to control item which is less than 250Vac and 10A.
A reverse diode
(1N4007) is connected with input of relay to avoid reverse spike or over current
flow back from the load. And a LED indicator is used to show relay is now On /
Off. When relay is On, LED is On. When relay is Off, LED is off.
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Circuit for Controlling an AC or other High-Current Device from a
Microcontroller by Using a Relay
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