HARDWARE SWITCH DEBOUNCER.
Debouncing switches is a technique used to ensure that the signal generated by a switch is clean and free of any noise or interference. Switches can generate multiple signals when they are pressed or released due to the physical characteristics of the switch. These signals can cause issues with the device that the switch is connected to.
Debouncing switches typically involves adding a small amount of delay to the switch signal. This delay allows any noise or interference to settle, ensuring that the signal generated by the switch is clean and consistent. There are two main methods that can be used to debounce switches:
- Hardware debounce: This involves adding a filter to the switch circuit to smooth out the signal and eliminate any noise or interference.
- Software debounce: This involves using code to add a delay to the switch signal. When the switch is pressed, the code waits for a certain amount of time before registering the signal. This delay allows any noise or interference to settle, ensuring that the signal generated by the switch is clean and consistent.
Overall, the goal of debouncing switches is to ensure that the signal generated by the switch is clean and consistent, even in the presence of noise or interference. This can help to prevent issues with the device that the switch is connected to and ensure reliable operation.
Pros of hardware debouncing:
- Simplicity: Hardware debouncing requires very little in terms of programming or setup, making it simple to implement in hardware designs.
- Efficiency: Hardware debouncing can be implemented using simple logic circuits and can work in real-time with little or no delay.
- Robustness: Hardware debouncing can be more robust against electrical noise and other environmental disturbances, as it operates at the hardware level.
Why do I use hardware debouncing in my projects? I follow a simple rule, if I can do something in hardware instead of software, I do it.
HOW DOES IT WORK.
Debouncing switches is the process of removing any unwanted noise or oscillations that occur when a switch is pressed or released. One common way to do this is by using a combination of an RC filter and an inverting Schmitt trigger.
An RC filter consists of a resistors (R1, R2) and a capacitor (C1). When a switch is pressed or released, the voltage across the RC filter changes rapidly, and this change is filtered by the RC circuit. When the switch is pressed, capacitor C1 is discharged via resistor R2 (τ = RC = 22ms). When the switch is released, capacitor C1 is charged via resistors R1+R2 (τ = 33ms). The capacitor acts as a short circuit to high-frequency noise, while the resistor slows down the charging and discharging of the capacitor, filtering out any lower frequency noise.
The output of the RC filter (Vin) is then fed into an inverting Schmitt trigger. The inverting Schmitt trigger circuit uses feedback to provide hysteresis, which is the ability to maintain a particular state even if the input signal changes. The hysteresis provides noise immunity and ensures that the output signal is clean and stable.
When a switch is pressed or released, the voltage across the RC filter will change rapidly, but the Schmitt trigger will only respond to changes that exceed its threshold levels. The combination of the RC filter and Schmitt trigger ensures that only clean, stable transitions are detected, effectively debouncing the switch.
In summary, debouncing switches via an RC filter and inverting Schmitt trigger involves using the RC filter to filter out noise and the Schmitt trigger to detect only clean, stable transitions.
CODING.
Using a hardware debouncer, program code for buttons is trivial. You don’t need to sample the state of the button when a button press is detected, you don’t need to keep an eye on the timing of button events, simple pin state detection is enough.
