When a mechanical relay switches on or off, the physical contacts inside do not make or break connection cleanly in a single smooth motion. Instead, they tend to flutter against each other for a brief moment—this phenomenon is known as relay bounce. These bounces can last from 1–5 ms, depending on the relay’s construction. During this time, the electrical connection produces erratic transitions, generating a series of unintended pulses instead of a smooth state change.
In simple circuits such as activating a heater, contact bounce might go unnoticed because the thermal inertia of the filament averages out the interruptions. However, in electronic systems that rely on digital logic, such as I, these false pulses can lead to system crashes. For example, one closure might be interpreted as several triggers, resulting in unintended behavior.
There are several effective ways to mitigate contact bounce. One common approach is hardware debouncing, which employs a resistor-capacitor رله network placed across the terminals of the relay contacts. The capacitor smooths voltage transients, allowing only the true contact condition to be detected by the downstream circuit. Another hardware method involves using a hysteresis gate, which has double switching thresholds to suppress noise and respond only to valid logic levels.
On the software side, debouncing can be handled by using a sampling interval after detecting a state change. For instance, when a embedded processor senses that a relay contact has opened, it ignores subsequent transitions—typically 5 to 20 milliseconds—before checking the signal stability. If the state is confirmed after the delay, the system accepts it as genuine. This method is widely used because it has zero hardware cost.
Some modern electronic relays eliminate contact bounce entirely because they contain no mechanical contacts. Instead of physical switches, they use MOSFETs to control current flow. While they may consume more power, they offer faster response times and are suited to avionics.
Ultimately, the choice of debouncing method depends on the system constraints. For basic projects, software debouncing is often adequate. For high-reliability systems, hardware debouncing may be preferable. Understanding contact bounce and how to address it is a critical design principle in building robust electromechanical systems.
