Nuts and Volts - October 2015

(milliseconds). The next step removes the sign and extracts the seconds from it. Now, the key: We take the modulus of 1,000 from the milliseconds register and if not 0, we bump the value in now. If now differs from last

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(both are global variables), we update the time display and then copy now into last.

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Finally, we check the value of now to see if the timer has expired; if it has, the program state is changed to S_HOLD and the timer is put on hold.

If a button was pressed (I favor active-high inputs), then we send that value to process_buttons and change the btimer milliseconds to the negative value of Before closing, let me share another trick I do with the timer — again, I used this with Brian's zombie escape room and the paratrooper training device. Each of them has buttons that need to be read frequently, and after a button is pressed, we need a hold-off period to prevent a quick back-and-forth state or value changes. For those programs, I did something like this:

pub check buttons | btns
 
  if (btimer.millis < 0)
 return
  else
 btimer.set(-BTN SCAN)
 
  btns :  read buttons
  if (btns <> %000000)
 process buttons(btns)
 btimer.set(-BTN
 HOLDOFF)

For the buttons, I create a separate timer object called btimer. The check_buttons routine gets called without delays from the main loop. When the milliseconds value of btimer is zero or positive, it is okay to scan the buttons. When this is the case, we set the next available scan time using BTN_SCAN (a constant I tend to set around 25). Now, we scan the buttons.