Switch debounce circuit uses only one gate

The circuit in Figure 1 produces a single debounced pulse each time you press S₁. Moreover, the circuit uses only logic power from the remote pull-up resistor, R₂. You can use the circuit to detect when a key is pressed in a non-energized device, such as a device in a system that’s just coming up from standby.

The circuit operates as follows: Assume that you have not yet pressed S₁ and that C₁ is in a charged state. Under these conditions, R₁ drives IC₁ toward V_SS (ground), causing the IC to consume virtually no power. This action allows V_OUT to remain near 5 V. However, when you press S₁, C₁ rapidly discharges and drives IC₁ toward V_DD. Under these circumstances, IC₁ conducts heavily, pulling V_OUT near 0 V until R₁ charges C₁ enough to again drive IC₁ toward V_SS. Once C₁ charges sufficiently, IC₁ goes to V_SS and stops drawing power. This action unloads V_DD and causes V_OUT to return to a high state. D₁ to D₃, in conjunction with R₃, shifts the level of V_OUT for improved compatibility with CMOS logic.

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