Software debounce switch

Again these switches come in different sizes and different current ratings. Because of such variations in switches, the bounce is also different in each type of switches. People press buttons in different ways. Some people press buttons very quickly, some push it very slowly, some users do it by hand, some use different objects to reach the switches. So designing the debouncing solution could be tricky sometimes. What type of switch you choose mainly depends on the application needs.

Once you know the bounce timing stats of a particular switch, you can easily design a debouncing policy.

The first crucial step is to find Maximum bounce time and that can be easily done by observing the voltage levels at the switch contacts using an oscilloscope.

Operate switch with different techniques, slow, fast, with soft-touch, with hard touch, release gently, release fast. Try different combinations of these techniques and collect the bounce statistics. With these statistics, you can easily arrive at the Maximum bounce time for your switches. The switch can have different bounce times when it is closed and when it is opened.

There are some proven techniques used to remove the effect of switch bounce in digital applications. You can use hardware or software debouncing methods. Hardware debouncing consists of simple hardware filters, digital debouncing circuits and dedicated ICs. The software debouncing method utilizes different algorithms, some are microcontroller platform dependant using specific interrupts , some use counters and some use simple delays before re-sampling the inputs.

Single throw buttons, tactile pushbuttons, and board mounted plates are the most common types of switches used in small appliances. Using a simple RC filter circuit is a lot cheaper solution than any other hardware debouncing technique. Low pass RC filter removes high-frequency changes in the switch bounce.

In time the capacitor charge and the output of the NOT gate Schmitt trigger give logical zero output. Till the time the capacitor is discharged to a significant level, NOT gate sees logical one at its input. And the NOT gate gives logical one output. V f is the final voltage of the charged capacitor. This can introduce errors in the system you are using and can hinder a lot of processes. Skip to content. Change Language. Related Articles.

Table of Contents. Improve Article. Save Article. Like Article. Software debouncing is accomplished by taking multiple samples of the input signal and determining whether to assert an output signal the debounced version of the signal HIGH or LOW based on whether consecutive samples are received.

For instance if two samples are both HIGH, and the time between them is much longer than the average duration of noise introduced by a bounce, then it is safe to say that the signal is in a HIGH state. Generally, only two samples are ever needed to accurately debounce a signal, provided that the period between samples is long enough. Figure 3 illustrates this algorithmic method of debouncing by showing a theoretical input signal and corresponding output signal the input signal is the one in gray; the output signal is the one in blue.

In this example, the debounced output signal remains LOW until time T4. The circuit set up for this project is identical to that of Blink LED with Trainable Delay, and the steps for setup will be simply reiterated. This step's purpose is to show the effects of button bounce and allows you to visualize when bounces occur in the circuit. If you feel you already have a firm understanding of bounce, you can skip this step and proceed to step 3.

In other words, the following code is only designed for the user to observe bounce it will not debounce the circuit. The code is fairly straightforward and all functions we use are from previous projects. The sketch reads the current state of the input button while keeping track of the state of the button from the previous loop of the main program. The sketch then increments a counter variable and outputs that value to the serial port.

You can view this count through the serial monitor window. Ideally, the sketch would increment the counter variable every time you press the button. However, after a few button presses, you will start to notice that sometimes the counter variable will increment multiple times.

In other words, you will press the button once, but you will see more than one counter value printed to the serial monitor. This happens because the program sketch has detected multiple rising edges in very close succession this occurs because of a button bounce. This code is extended to provide a button press counter capability by counting rising edges to verify the code is operating correctly.

The debouncing algorithm used for this sketch at first may appear slightly different than our theoretical explanation, but once examined you can see the differences are only marginal. When analyzing the debouncing algorithm used for our sketch, we only look at the point when the input signal changes as opposed to taking a periodic time sample like our theory explanation suggested.