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Separate ON-OFF Touch Switch(BC557)

2015-09-01 01:58  
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This article describes the Separate ON-OFF Touch Switch (BC557). The principle is very simple, very practical. The circuit components can help you understand better grasp this principle. For example, in this circuit, you can go to find and buy these components: BC557.

This schematic diagram is about touch switch circuit. Separate ON andOFFswitch improves the ergonomics for safety, since the touching off button when the state is off doesn’t make the system acts in the opposite way: turning ON the system. This accident usually happens when we make wrong assumption of the current state about ON orOFFof the system while the function of the switch depends on it previous state.

Circuit diagram:


Figure 1 

This circuit turned on when the super-alpha pair of transistors receives a very small current from detected the skin resistance of a finger. The BC557 transistor turned on by he output of the “super transistor”. To keep the circuit remains ON, the voltage on the top of the bulb is passed to the front of the circuit via the 4M7 to take the place of the finger. When a finger on theOFFpads, the first transistor will be activated and the voltage of the “Darlington pair transistor” will be decreased and the circuit will turnOFF.



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