What does it do?
|The switch subsystem provides a switch that closes when pressed. The output signal from the switch subsystem goes high when the switch is pressed.
How does it operate?
Click on the circuit diagram to download a Livewire file of the Push Switch that you can investigate and add to your own circuit.
The switch circuit uses a push-to-make switch:
The push switch forms part of a potential divider whose output voltage is determined by the upper and lower parts of the circuit.
When the switch is not pressed its resistance is very high and the output signal is low. When the switch is pressed its resistance is very low and the output signal is high.
Instead of using a push switch, a slide switch (that stays in the on or off position) or a microswitch (that is designed to be pushed by an object) can be used.
It is also possible to manufacture contact switches in various ways.
- Providing a signal to make something start or stop
- Sensing an object (microswitch)
How part of the PCB might look
Use a multimeter (on the resistance setting) to check that the switch is working before soldering it in place.
Make sure that the signal going out (on the green PCB track) changes from low to high when the push switch is pressed.
If there is a fault, check that:
- The voltage at the ‘bottom’ connection of the resistor is low (0V)
- The voltage on the ‘top’ pin of the push switch is high (the supply voltage)
If there is a fault, check the tracks and solder joints.
- A slide switch or a microswitch can be used in place of the push switch
- Quantum Tunnelling Composite (QTC) is a recently developed material that can be used to make up low cost switches.
- Optoswitches are useful for detecting when an object is near to the sensor, but they are more expensive.
- Some push switches are designed for mounting on the PCB; some are ‘panel-mounted’ (for mounting on the case).
- Switches come in a wide range of shapes and colours.
- Keypads are a matrix of push switches and can be used to enter data. They are more sophisticated and more expensive.
- A Hall effect sensor can be used to detect if a magnet is close.
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