Schmitt Trigger: Robust Comparator Design with Hysteresis
A Schmitt trigger is a comparator with built-in hysteresis, ensuring clean digital output even with noisy or slow inputs. This article covers the principles, derives threshold voltages for inverting and non-inverting op-amp circuits, explores discrete BJT implementations, and compares integrated CMOS Schmitt-trigger inverters like the SN74HC14 and SN74LVC1G14. It also discusses comparator ICs with adjustable hysteresis and practical applications such as debouncing, zero-cross detection, and relaxation oscillators.
Hysteresis is essential in many embedded systems: it debounces mechanical switches, shapes waveforms, prevents oscillation when sampling analog levels, and enables simple oscillators.
- wrigby
It's worth point out that on many microcontrollers (STM32's at least), configuring a pin as a "digital input" means that the signal is routed through a Schmitt trigger circuit that's built into the MCU.
This also means you'll want to ensure that any floating MCU pins are _not_ configured as digital inputs, as the Schmitt trigger circuit itself will waste power switching back and forth between high and low states constantly.
- aappleby
Slop