Elektor Circuit: Touch Doorbell with 555

Idea: Elektor Lab

The great advantage of a touch button or switch is the absence of mechanical parts — what is not in it cannot be broken. Because old-fashioned doorbell push buttons are exposed to wind and weather, they become unreliable over time. So why not replace them with a touch button?

Figure 1 shows the diagram of our touch doorbell. The touch switch on the left side consists of two pieces of metal close to each other (how you construct it is left to your imagination). As soon as both contacts are touched, the rather large (about 1 MΩ) skin resistance allows a small current to flow to ground via resistor R3. Because R3 is very large (22 MΩ!), pin 2 of IC1 is pulled down enough to trigger the good-old 555.

Elektor Circuit: Touch Doorbell with 555 – [Link]

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