A sensor is a device that replaces a button, which is triggered not by pressing, but by touch. It can be electrical or optical. The way it is turned on depends on the chosen physical principle of operation.
Instructions
Step 1
The sensors that react to interference only work in rooms where there is an AC mains. When a person is in such a room, his body, like an antenna, perceives the radiation of the wiring. When the sensor is touched, the voltage induced on its body is detected and causes the transistor to open. To make such a sensor work, make a voltage doubling diode detector. Connect its input to the sensor, and the output to the base of the transistor operating in the key mode and connected according to the scheme with a common emitter. Use a high-resistance load, otherwise the transistor will not saturate. When you touch the sensor, a constant voltage will appear at the output of the detector, a current will flow between the base and the emitter of the transistor, and it will open. The voltage between its collector and common wire will drop to zero.
Step 2
Sensors, consisting not of one, but of two plates, are triggered when a finger closes one of them to the other. Connect a zener diode between the plates in the opposite polarity of the power supply. The stabilization voltage of the zener diode should be about 20 V. Connect one plate to the common wire, the second through a 10 kΩ resistor to the input of the logic element of the K561LN2 microcircuit. Also connect the same input to the CMOS power rail through a 10 MΩ resistor. Now, if you do not touch the plates, the output will be a logical zero, and when the plates are closed, a logical one. Such a sensor will also work in a room where there is no electrical wiring.
Step 3
In the past, limited use was found for sensor devices that respond to the breakdown of oscillations of the generator when the plate is touched. If you wish, you can build such a device now. Take the circuit of any capacitive relay as a basis. Instead of an antenna, connect a sensor to it, but not directly, but through a 1 MΩ resistor. Select its value in such a way that the operation occurs only when you touch the plate, but not when you approach it.
Step 4
The optical sensor is an optocoupler with an open optical channel. Connect the emitting diode of such an optocoupler to the power source through a resistor selected so that the current in the circuit is equal to the nominal current for the diode. Connect the emitter of the phototransistor of the optocoupler to the common wire, the collector through a 1 kΩ resistor to the CMOS logic power bus. In addition, connect the collector to the input of the logic element of the K561LN2 microcircuit. The logical unit at the output of this element will change to zero when the luminous flux is interrupted by a finger. To reverse the logic of the device, use another logic element of the same microcircuit.
