Answer6

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Problem 6—Design a simple circuit with minimal components for de-bouncing a push button switch. Answer: Many times, SPST push button switches are used in digital circuits. In such cases, an ordinary SR flip flop cannot be used to debounce the contacts. The circuit shown below can be used instead. When the push button S is open, the output is pulled high by the resistor R. Now, if S is closed, the capacitor immediately charges to Vcc and the output becomes zero. This voltage is maintained across the capacitor and the output remains zero until the capacitor discharges through the resistor R. Any further makes and breaks of the switch while the capacitor is charged does not alter the output and it remains at zero until the capacitor discharges. This effectively de-bounces the switch. A schmitt inverter can be used at the output to get fast changing output waveform. The RC time constant is chosen to be about 20 - 100ms in most applications. Contributor: Naveen P N 4-01 — NEXT Q&A For questions or comments about Test Your EQ, e-mail eq@circuitcellar.com.