Electrical Issue: PIC input false triggering, Signal Noise suspected.

[richard]

another way is to filter the input with a software routine

reeds var byte
reeds_flg var byte
reed_1_active var reeds_flg.0            
reed_2_active var reeds_flg.1
reed_3_active var reeds_flg.2
reed_cnt var byte[3]
reed var byte
define reed_threshold 64

chk_reeds:
reeds=portc & $70  ;c4 c5 c6  active low
if reeds < 112 then
reeds=reeds >> 4
for reed = 0 to 2
if ! reeds.0 then
        reed_cnt[reed]=reed_cnt[reed]+1 
        if reed_cnt[reed]> reed_threshold then reeds_flg.0[reed]=1
else
        reed_cnt[reed]=0
endif

reeds=reeds>>1
next
endif
return

if you call the chk_reeds subroutine regularly (must be regular) say in this case 100 times per second, then if a reed input is consistently low for 64 (counts in a row the reed_threshold) then the reed_x_active flag will be set.

[abecker]

Thanks Richard.

This has great potential in my code because as you commented, once I set close the realys to the trolley power all I have to do is loop through the routine that checks for a low sensor. To make it easier, the trolley dbeing on a track can only go in on direction at a time so in each stage of travel I know exactly which sensor to poll. Not like I would need an interrupt to see which of the three sensors went low. The time the magnet is over the reed switch is eon's compared to the rate at which the pic can poll the sensor line.

As I mentioned to one other reply, the pic advances to the next logical set of events just when the trolley gets moving and is several feet away from any sensor. This is what leads me to think some DC motor noise or even arcing of the pickup on the overhead wire is being picked up at the sensor pins and causing a false signal.

I will study your code and possibly with it and many of the other outstanding suggestions here, find a solution which I will gladly report on.