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2-Wire Interface for Illuminated Pushbuttons

Cut down on cabling to improve reliability

Reducing the number of interconnections in a design improves system reliability. There are fewer problems of unreliable contacts and cable failures. This design shows how you can get away with just two wires instead of the more usual three when connecting an indicator pushbutton.Engineers are no friends of a wiring rat’s nest. More cables means more connections means more chance of an unreliable system.

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winzurf 2 years ago

The obvious drawback of this circuit is the led cannot be illuminated while the button is pressed, so if the user is looking for confirmation they may hold down the button waiting for a response which will never come. One solution would be to have a resistor in parallel with the led (R1), and a second in series (R2), with the switch in parallel with R2. For small drive currents the voltage across R1 would be insufficient to turn on the led, while increasing the current would activate the led. In both cases pressing the switch would change the applied voltage and be detected by the driving circuit.

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