Edge Detection

JTay

Hi, how·to detect leading/falling edge of a pulse using basic stamp?

Bruce Bates

JTay -

There is no easy or automatic way to do it, as far as I know, except that you can realize a 1-0-1 or 0-1-0 transition with PULSIN. If you only want to detect 0-1 or 1-0 then you must do it manually. Here is the basic untested process, although there may be simpler ways of doing it:

/code

pulsed_pin pin p0 ' arbitrarily check pin port 0

First_Status: 'Very first excursion ONLY otherwise use Check_Pin: entry

curr_status = pulsed_pin 'Save current pin state
last_status = curr_status 'Dummy last pin state

Check_Pin: 'Normal entry point

curr_status = pulsed_pin 'Fetch current pin state
· IF curr_status <> last_status GOTO pin_change 'Has there been an edge transition?

GOTO Check_Pin 'No edge transition occured

Pin_Change: 'Edge transition occured, check which way
· IF curr_status < last_status GOTO Low_Trans: 'Did it go high to low

High_Trans: 'Transition was low to high


trans_state = 1 ' set direction of transition
GOTO Trans_Occurred 'Prepare to exit

Low_Trans:


trans_state = 0 ' set direction of transition

Trans_Occured: 'Prepare to exit

last_status = curr_status

code/

That should get you started.

Regards,

Bruce Bates

Post Edited (Bruce Bates) : 12/30/2005 6:52:16 AM GMT

JTay

thanks a lot Bruce! u have given me a good starting point.

I was hoping there might be a simple way by using probably polling or interrupts to detect edges, but i think this shd be able to do the job. thks!!