Digital I/O Help

[RedOctober]

How do I use the I/O's to sense an external input, such as a switch, particularly a limit switch. For example, if I want to count how many times the switch was pressed, meaning that the digital input detects a "high" signal and can then count a variable each time this happens, in code. I been trying to mess with it but I do not much experience with this type of custom configuration. I been trying to set up the digital inputs to detect a high signal and then a different one output a certain signal but with no luck. Thanks for any help with this.

[Ryan M.]

There are two ways you can do what you want. The first is the easy way:

1. Create either a global variable or a static local variable where you will store your count
2. Somewhere in the 26.2 ms loop area, have an if statement which increments the variable if the digital io is pressed. IE:
   

   if(digital_io_01 == 0) // Note that the inputs are pulled high, so when the sensor is indicating it is pressed, you are actually getting 0
       countVariable++;

The second way involves using interrupts and is slightly more difficult, but necessary if you are going to be getting digital IO state changes at a high rate. (An encoder on a drive wheel would be an example of something which typically needs interrutps.)

[Alan Anderson]

The digital inputs on the RC will read as "1" when open, and "0" when grounded. They will directly detect contact closures to ground, such as a limit switch or an Allen-Bradley optical sensor.

If you want your code to count switch activations, you should remember that you only want to increment the count when the read value changes from 1 to 0.

  if (last_rc_dig_07 == 1 && rc_dig_07 == 0)
    switch_counter++;
  last_rc_dig_07 = rc_dig_07;