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Company Logo NXP Semiconductors

  • Simple Electronic Touch Switch

  • Created: Jan 28, 2014

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The circuit is ideal in applications that would require an alarm in the presence of touch contact. A simple application is a doorbell system which can be switched on by simply touching the sensors. the circuit can also be used as a touch sensor to indicate a warning when the user is in contact with a potentially hazardous area. This circuit is also applicable to touch switching in home/office lighting or appliances. The circuit is a diagram of a simple touch sensing network which uses the NOR gates as simple latching circuits to prevent fluctuation between the ON and OFF states. When contact is made on T1 and T2, or, T3 and T4, the output mechanism (which may be a LED indicator) is triggered ON and OFF respectively. The circuit contains touch sensors at the input side, NOR gates, a transistor, and an output mechanism. The touch sensors operate by utilizing the conductive characteristics of the human hand; a closed circuit will be established between the adjacent sensors and will send a signal to the logic gates about the sensor states. The NOR gates will compare the states of the sensors, and for this circuit, the 74HC02BQ quad 2- input NOR gate is used. The IC has four NOR gates packed into a single integrated circuit. The transistor BC859 is used to amplify the output from the NOR gate to drive the output mechanism. The output mechanism may be in the form of a buzzer or a Light Emitting Diode (LED) to indicate the connection.

1 Comment


Not your fault, but this would be much simpler to understand if the schematic symbol showed individual NOR gates so that people could see how they are wired up. After all, the whole point of a schematic over a pictorial diagram is clarity.

Posted: Sep 14, 2017



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