Objective:to know about push button
and relay circuit
A relay is a simple
electromechanical switch made up of an electromagnet and a set of contacts.
This is relay Single Pole Single Throw (SPST). Current flow through the coil of
the relay creates a magnetic field which attracts a lever and changes the switch
contacts. The coil current can be ON or OFF so relay have two switch positions
and they are double throw (changeover) switches. Relays allow one circuit to switch
a second circuit which can be completely separate from the first. For example a
low voltage battery circuit can use a relay to switch a 230V AC mains circuit.
There is no electrical connection inside the relay between the two circuits;
the link is magnetic and mechanical. The coil of a relay passes a relatively
large current, typically 22.2mA for a 9V relay. Most ICs (chips) cannot provide
this current and a transistor is
usually used to amplify the small IC current to the larger value required for
the relay coil. Relays are usually Single Pole Double Throw (SPDT) or Double
Pole Double Throw (DPDT) but they can have many more sets of switch contacts,
for example relays with 4 sets of changeover contacts are readily available. Besides,
the transistor used to amplify the current for the relay is an NPN transistor,
C547
Push
Button as input for PIC Microcontroller
One
I/O pin is needed for one push button as input of PIC microcontroller. The
connection of the push button to the I/O pin is shown in Figure 48. The I/O pin
should be connect to 5V using a resistor 10K. Other than that, the value range for
the resistor can use between 1K until 10K. This configuration will result an
active-low input. When the button is being pressed, reading of I/O pin will be
in logic 0, while when the button is not pressed, reading of that I/O pin will
be logic 1
Relay Circuit
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