#537 Schmitt Switch Debouncer
Testing a simple Schmitt Trigger debounce circuit using a 74HC14.
The hysteresis of a Schmitt Trigger used in conjunction with a suitable RC filter provides effective switch debouncing:
- the RC time constant for charge/discharge filters most of the switch bounce
- Schmitt Trigger hysteresis can help with ensuring positive on and off transitions
The circuit demonstrated here is based on Experiment #125 from ARRL’s Hands-On Radio Experiments Volume 3.
I’ve put double-inversion in the circuit; the result is that the LED is normally on, and turns off while the pushbutton is depressed.
Time constants are purposely large:
R2 needs to be much less than R1, else pressing the button will not pull down the voltage sufficient to switch the inverter.
The on-off cycle is captured in the following scope trace where
- CH1 (Yellow) - switch output
- CH2 (Blue) - inverter input
- CH3 (Red) - output to LED
Credits and References
- ARRL’s Hands-On Radio Experiments Volume 3 Experiment #125
- 74HC14 Datasheet