Modern mechanical switches reliable, convenient and cheap. But sometimes it takes a switch actuated without the application of mechanical force. If we use the proposed device, for switching on or off the load is sufficiently light touch to the metal plate sensor.
Diagram of the touch switch shown in the figure.
The master oscillator to the elements DD1.1, DD1.3 produces a pulse frequency of approximately 12 kHz and swing close to the supply voltage (12V). With output 4 of the element DD1.3 pulses through capacitors C4 and C5 to the input of the element DD1.4, working in the linear mode and the employee amplifier.
Further, the pulse is differentiated by the circuit C6R5R6, through the element DD1.2 go to the rectifier (diode VD1). The DC voltage at the output of the rectifier corresponds to the amplitude of the pulses.
Sensor E1 - metal plate connected to the connection point capacitors C4 and C5. Touching the plate sumikat this point to ground through active-capacitive resistance of the human body. As a result of sharply decreases the amplitude of the pulses at the inputs of the element DD1.4. Accordingly changes the output voltage of the rectifier: with approximately 8 In (up to touching the sensor) to almost zero (after touch). Logic low the level at the output of the element DD2.1 is replaced by high. This drop through the capacitor C1 is fed to the input 13 of the element DD1.2 and supports at its output and the output of the rectifier, the low level irrespective of the presence or absence pulses at the input 12.
Duration of preservation of this state is determined by the time constant circuit R1C1 and sostavljaet approximately 0.5 seconds.
The signal from the output of the element DD2.1 is input to J, he, pronor targeted with using the element DD2.2, is input To the trigger DD3.1. HB the counting input of this the trigger receives the pulses of the master oscillator (pin 3 of the element DD1.1). This allows you to avoid the "bounce" and provides a clear single switch and the reset trigger DD3.1 every time you touch the sensor.
The trigger DD3.2 operates in a counting mode, changing the status to opposite at each reception of a pulse output from the DD3.1. With the release of the trigger DD3.2 connected key on the transistor VT1. It controls the relay K1, the winding of which included in the collector circuit of the transistor is shunted by the diode VD2, extinguishing release tension in the moment of switching off the relay.
Relay contacts K1 commute nagruzke. In the original LRA lamp table lamp, made of twigs. Used relay RES, passport RS4.569.435-02. The current consumed by the switch circuit 12 V, - 12 mA in idle mode and 26 mA - triggered relay. The switch can be powered from any source to satisfy the above voltage and current.
Relay K1 should be chosen contacts that can withstand the current and voltage of load switch, and capacitors C4 and C5 - for a voltage of less than 400 In the Past ensures electrical safety of the device when it is powered transformerless source.
Author: O. ceremony, St. Petersburg