Micro switches are very common devices. They are used in consumer devices, industrial equipment and more.
One of the most common applications for these devices is in door interlocks. These are common in consumer devices, notably in microwave ovens, where the door has to be shut before the power to the device will turn on.
Micro switches are also used in leveling devices, such as those used on vending machines. In an elevator, these devices are used in the door as a safety switch. The devices are also used to detect whether paper is jammed in a copier and for myriad other purposes.
Micro switches can be designed to be very sensitive. Such designs can be used in very precise equipment, such as that which measures the flow of air or other gasses through a system. They can also be used to detect pressure and temperature.
These devices are used extensively in industry, often in control circuits. They are sometimes employed as the direct means of turning equipment on and off, as well.
User Input
Of course, user input is one of the more common applications for switches. For example, if you want to connect a switch to a microcontroller input pin, a simple circuit like this is all you'd need:
When the switch is open, the MCU pin is connected through the resistor to 5V. When the switch is closed, the pin is tied directly to GND. The resistor in that circuit is a pull-up resistor, required to bias the input high, and prevent a short to ground when the switch is closed.
On/Off Control
Among the most obvious of switch applications is simple on and off control. The type of control you perform every time you walk into a dark room. An on/off switch can be implemented by simply sticking an SPST switch in series with a power-line. Usually the on/off switch will be maintained, like a toggle or slide switch, but momentary on/off switches can have their purpose.
On this Breadboard Power Supply, an SPDT switch is used to turn the circuit on and off. (A second SPDT switch is used to select the adjustable voltage regulator's output value by adjusting a voltage divider.)
When implementing such a switch, keep in mind that all the current your project consumes is going to run through that switch. Ideally a switch is a perfect conductor, but realistically it's got a small amount of resistance between the two contacts. Because of that resistance, all switches are rated for a maximum amount of current they can withstand. Exceed a switch's maximum current rating, and you can expect melted plastic and magic smoke.
Resources and Going Further
Well, that about covers the basics of switches. Next up, you could explore some of these other conceptual tutorials:
Transistors - These can be used (among many other things) as sort-of electronically controlled switches.
Pull-up Resistors - Pull-up resistors complement most momentary button circuits. They ensure that power and ground don’t short, and they make sure I/O lines don’t float.
Accelerometer Basics - Motion-sensing accelerometers -- like those in most smartphones and new video game controllers -- are fast-replacing these boring switches as human input devices.
Relays - Another electronically controlled switch. Great for turning on and off high-power circuits.
How to Power a Project - What kind of power source will your switch be turning on and off?
Or check out some of our project tutorials for some inspiration for your own projects. Switches are so widely used, we could probably link all of our projects. But here are a couple which make really ingenious use of switches to do their thing:
The Uncertain 7-Cube - Well, this project doesn’t actually have any switches, but that’s what makes it so special! This project is a great example of how an accelerometer could replace a switch as an input device.
MP3 Player Shield Music Box - This project (bigger on the inside) uses one of those non-traditional switches -- a reed switch -- to trigger it’s action.
Reaction Timer - Use giant dome push buttons to create a fun reaction game.
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