Touch Switch | Electronic Project Circuits

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Electronic Touch Switch

Mechanical contacts have the disadvantage that they wear out. That is why it is practical to use an electronic ‘touch switch’ in some situations. With such a touch switch the resistance of the human skin is used for the switching action. The schematic shows the design of a circuit that senses the resistance of the skin and converts it into a useful switching signal. The touch switch contacts can be made from two small metal plates, rivets, nails, etcetera, which are placed close together on a non-conducting surface.

In this circuit a comparator of the type LM393 has been used. In the idle state there is, via R1, a voltage equal to the power supply voltage on the non-inverting input of IC1a. Because the inverting input of IC1a is set with R2 and D3 to D5 at the supply voltage minus 1.8 V, the open-collector output of IC1.a is, via R3, equal to the power supply voltage. This voltage is inverted by IC1.b. The voltage at the non-inverting input of IC1.b amounts to half the power supply voltage (through voltage divider R4 and R5) and is lower than the voltage on the inverting input.
The output of IC1.b is therefore a ‘0’. If the two touch contacts are bridged with a finger, the voltage at the non-inverting input will become low enough to cause the comparator to toggle state. The moistness of the skin results in a resistance of 1 to 10 MR. If this circuit is used in the vicinity of equipment that’s connected to the mains, then it can be sufficient to touch only the upper contact to operate the switch, provided that the circuit has been earthed. The body then acts as an antenna which receives the 50 Hz (or 60 Hz) from the mains.

This is enough to toggle IC1.a at the same 50 Hz. C1/R3 prevent this 50 Hz from reaching the input of IC1b and provide a useable ‘pulse’ of about 10 s at the output of IC1.b. Note that a fly walking across the touch switch conducts enough to generate a switching signal. So do not operate important things with this circuit (such as the heating system or the garage door). Do not make the wires between the touch contacts and the circuit too long to prevent picking up interference. The power supply voltage for the circuit is not very critical. Any regulated DC voltage in the range from 6 to 20 V can be used.
Author: Heino Peters – Copyright: Elektor Electronics Magazine
Read more : http://www.extremecircuits.net/2010/06/electronic-touch-switch_03.html

Be the first to comment - What do you think? Posted by admin - February 21, 2011 at 9:42 pm

Categories: Electronic Control Tags: lm393, touch switch

Touch Motor Control by SCR and Schmitt Trigger

This circuit designs for control DC Motor 12Volt. By use the touch once Motor as a result turn go to once. When use a finger touches the metal makes Schmitt Trigger Circuit take a signal from Oscillator Circuit and make a signal goes out Trig SCR Bias Current the DC Motor 12V then turn follow want. For power supply type of DC Motor this must be AC 12Volt Only. because of make SCR not bias during negative current there. And this circuit works not heavy DC motor, turn ? do not turn ? Then don’t have to stick heat sink give SCR1 for DC motor you will may use motor at use in an automobile all right. Request enjoy please, sir.

Be the first to comment - What do you think? Posted by admin - September 13, 2008 at 9:32 am

Categories: Electronic Control, Motor controller Tags: circuit SCR, dc motor drive, schmitt trigger circuit, touch switch

Touch Switch using UJT 2N3819

This be Very Simple Touch Switch Circuit. It used UJT 2N3819 is Main part numbers should set up this outside building circuit. When stay far from electric line or Power Line very much. Enough touch at infront touch 1 metal and 2 make Relay work ON get. When but urgent touch 2 metals only make Relay stop work OFF get. For within a building must enhance the part mends or infront touch 3 metals with follow circuit picture. The Relay use 6V to 9V sizes and Volt supply use 6V to 9V levels all right sir. Request friends have fun Touch Switch using UJT 2N3819 , please sir.