Circuit Lake

Many embedded microcomputer projects require one or more switches for the users to control some function. It is possible to replace mechanical switches with touch-switches, which have several advantages: reliability, contamination tolerance, quiet operation, and a space-age gee-whiz factor that may help sales in some markets. With the recent development of low cost integrated circuits for doing touch-switches, using them may actually lower costs.

This project shows a method for doing almost-free touch-switches that do not require additional hardware, except for a small capacitor and some printed-circuit board area. This method requires two free I/O pins on the microcomputer for each switch. A test module built on the Microchip PIC24 Starter Board is used to test the display module. Software and a description of the test module is included so that readers may duplicate both the Lin-Touch-Display module and the test module that is used to verify correct functionality.

Glen Worstell, the project designer, said that the system is simple in concept. Operators use the touch switch to indicate desired control or display information to the master, with the data transferred using LIN. The module is general-purpose, and can be used for many different applications. The breadboard module has two touch-switches, although only one is currently used. Touch switches are almost free, requiring only two GPIO pins and a small capacitor for each switch (plus some PCB area for the actual touch interface).

LIN Touch-Switch
Download Project Documentation (zip)
circuitcellar.com