INPUT DEVICES – SENSORS
Every electronic circuit must have some kind of input device so that we (the outside world) can "communicate" with it.
THE SWITCH
When the switch is closed it allows current to flow through it.TYPES OF SWITCH
There are various types of switches that can do slightly different jobs in a circuit
SPST - sinqle pole, single throw
SPDT - single pole, double throw
DPST - double pole, double throw
DPDT - double pole, double throw
The diagrams show you examples of each type.
STUDENT INVESTIGATION
Which switch would you use to:
(a) change the direction of an electric motor
(b) switch on a light
(c) switch off a green light and switch on a red light
(d) switch on two motors at once
Which switch would you use to:
(a) change the direction of an electric motor
(b) switch on a light
(c) switch off a green light and switch on a red light
(d) switch on two motors at once
THE LIGHT DEPENDENT RESISTOR
This is a resistor which has a resistance that changes with the amount of LIGHT that falls on It. In the DARK its resistance is LARGE (millions of ohms), in the LIGHT its resistance is SMALL (tens of ohms). Very little current will flow through It In the dark.THE THERMISTOR
This is a type resistor which has a resistance that changes with TEMPERATURE. In the COLD its resistance is LARGE (thousands of ohms), in the HEAT its resistance is SMALL (tens of ohms). Very little current will flow through it when it is cold.