It can be seen from the figure that there is a difference between the ideal waveform and the actual waveform. The real signal shows some jitter at the moment of pressing and releasing the button. This jitter is caused by the mechanical characteristics of the switch, typically lasting 5 to 10 milliseconds. When we manually press and release a button, the time it takes for the contact to stabilize is usually more than 20 milliseconds. Therefore, when detecting whether a key is pressed, the MCU should implement a debouncing mechanism to avoid false triggers.
There are dedicated hardware circuits and specialized debounce chips available, but in most cases, software-based debouncing is commonly used. One simple method is to introduce a short delay after detecting a key press, then re-check the state of the input. If the signal remains stable, it's considered a valid press.
Here’s an example of how this might be implemented in code:
```c
if (0 == K1) // Check if the key is pressed
{
Delay_ms(8); // Wait for a short period to allow the signal to stabilize
if (0 == K1) // Confirm the key is still pressed
{
// Perform the desired action here
}
while (!K1); // Wait until the key is released
}
```
Although software debouncing ensures reliable detection, some may question its necessity. Jitter occurs only during the physical movement of the button. If the button is not pressed, the I/O pin should remain stable. However, in practice, even without a button press, noise or interference can cause temporary fluctuations on the input line.
The main concern with jitter is that it may lead to multiple detections for a single press. For example, if the system processes a key press and executes a function, but the function runs faster than the jitter duration, it could trigger the same action again. This is especially problematic in systems where repeated actions are not desired.
To prevent this, debouncing ensures that each button press is recognized only once. It’s important to design the system so that after a key is detected, it waits until the signal stabilizes before taking any further action. This way, the system avoids unintended repetitions and improves overall reliability.
In summary, debouncing is crucial for ensuring accurate and consistent key detection. While it may seem unnecessary in some cases, it plays a vital role in preventing errors caused by mechanical instability. Whether using hardware or software methods, proper debouncing is essential for reliable user input handling.
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