Relays are traditional building blocks in control devices. Their advantage is that a relatively small power is necessary to operate the relay coil, but the relay can switch relatively high currents or voltages and to control motors, lamps, heaters and other devices that use more electrical power.
There is a huge variety of switching circuits that use relays. When managed with microcontrollers it's very simple and easy way to make complex applications. The input can be from switch buttons, keyboard or different sensors.
Here are some examples for relay solutions.
Dental cup filling module
Several solutions are possible:
1. The dentist presses button and keeps it on until the cup is filled.
2. The dentist presses button, the cup starts to fill, second pressing stops the filling - this solution is made with trigger scheme.
3. The dentist presses button and the cup fills for a fixed time - this solution is made with multivibrator scheme.
In all these solutions the dentist will have to watch whether the cup is in its place and whether it is full.
The process can be automated with microcontroller scheme and 2 sensors - one for the place of the cup and one for the level of water in it.
Semi-automatic solution - the dentist presses button and if the cup is in its place it fills.
Automatic solution - on putting the cup in its place it fills.
Temperature regulator for control of the heating system can be made with microcontroller, temperature sensor and potentiometer.
The temperature is fixed with potentiometer. The temperature sensor measures the temperature and the regulator switches on the heating system when the temperature goes under fixed value. When the value of the temperature is reached regulator switches off the heating system.