Implement Debounce Function for SPDT Switch on Mbed NXP LPC1768


  • Host PC: Ubuntu 18.04
  • Device: mbed NXP LPC1768
  • Switch: EG2350-ND

Experiment to Measure a Chattering Event

mbedLearning/main.cpp at master · shirokunet/mbedLearning

The result is depends on switch mode such as pullup and pulldown. But the chattering time I detected is about ~800 usec.

PullUp Mode

PullDown Mode

How to Implement Debounce Function

Basically, when using a switch or a relay, chattering will be caused. To solve this problem, two solution can be used. One is create a LPF circuit using a resistor and a capacitor. It cuts high frequency noise such as chattering. However, we have to change hardware. Another solution is counting time after detect rise edge using interrupt on the software. This implementation is easier than LPF. But we have to care about using this solution because interrupt function can interference other function.

I chose second solution which is using software.

10th Count Application

Here is example of count application.