Use a switch by change not on/off status.

[courtec]

Dear all,

I have a problem with a toggle switch where the output must change on a status on a switch going from 1 to 0 or vice versa.
To read a 0 or 1 from a switch is no problem. I need to read the flank, like a flipflop does. Is the right way an interrupt?
The output must remain 0 on startup, regardless the on or off status of the switch.
Any help appreciated.

Thanks,
Koert

[Ioannis]

Interrupt sure is one way. Maybe PulsIn is another, to read the edge of the pulse.

Ioannis

[rsocor01]

The output must remain 0 on startup, regardless the on or off status of the switch.

What exactly do you mean by that? Do you mean a logical 0 in the program algorithm or 0 volts at the switch? There are a few ways to do it depending on what you want.

[Demon]

Off the top of my head in pseudo-code:

SwitchIn VAR PortB.0
OldState VAR BIT
SwitchState VAR BIT

OldState = SwitchIn
SwitchState = 0

Main:
  IF SwitchIn not = OldState THEN
    SwitchState = SwitchState ^ %1  ' Switch has been toggled
    OldState = SwitchIn
  ENF-IF
GOTO Main

Robert

[Archangel]

I would use interrupt on change. ISR just changes output port status. Set port status in start up code to " your safe off status" set interrupts off until pic is stable then enable interrupts. Whatever status toggle switch is in initally is irrelevant as changing it triggers the interrupt.

[Demon]

Interrupt on change is more efficient. But this is Koert's first post and he just joined, he hasn't given any indication to his level of PBP expertise..

Assuming he is a beginner, he's better off trying logic instead of interrupts to get the ball started, then switch to interrupts later as a challenge.

Koert, search for Darrel Taylor's Instant Interrupts in FAQ section. Unless you only do super simple programming, they help A LOT when using USB, timers, interrupts, and many more features.

Robert

[richard]

I agree with Robert contact bounce and such can really confuse an interrupt based solution ,unless you have some experience behind you. slow changing inputs can easily be read (and debounced) by using polling style solutions

[Archangel]

contact bounce can be marginalized with a short pause. IOC would trigger going to either logic state and his output would always start out at what it is initialized to. If he is not too worried about latency then even ON INTERRUPT would work, though I prefer Darrel's asm interrupts.

[courtec]

Thank you all for the input so far. And indeed, I am new with pic programming. Knowledge of basic language and electronics for many years. This kind of switching solution was done by a 4027 JK flipflop. But it's time to move on and use a micro controller. And more of a challenge then i expected!
Anyway, to be more precise about the question asked:
a micro switch in a machine is standard closed by a magnet.
When the switch opens, so goes from 0 to 1 (logical) a relais must be activated. When the magnet returns and the switch goes back to 0, doe nothing
Again when the switch opens again toggle the relais. All with sufficient code to avoid bouncing.
'
Quite simpel i think but several programs i tried don't work as good as a 4027. "Probably" due to the fact that i am a new-be....

I'l look into the two solutions mentioned and let you know. Thanks again.

Koert.

[Ioannis]

Try this. I have not tested though, but is based on Roberts idea to work as you requested. Roberts idea will toggle the output everytime the switch will change state. Not on 0->1 only.

SwitchIn VAR PortB.0
OldState VAR BIT
SwitchState VAR BIT

OldState = SwitchIn
SwitchState = 0

Main:
  IF SwitchIn not = OldState THEN
    IF SwitchIn THEN
      SwitchState = SwitchState ^ %1  ' Switch has been toggled
    ENDIF
  ENDIF
OldState = SwitchIn
GOTO Main

Ioannis

[Demon]

You can tweak a PAUSE 50 before GOTO as simple debounce.

Robert

[Ioannis]

I think debounce is not necessary since he wants to see the edge from 0->1 and toggle the output. Then do nothing with 1->0 until a new 0->1 edge comes.

Ioannis

[Demon]

I know, I was just suggesting minimal debounce as he requested.

All with sufficient code to avoid bouncing.

Robert

[killdill045]

Set port status in start up code to " your safe off status" set interrupts off until pic is stable then enable interrupts. Whatever status toggle switch is in initally is irrelevant as changing it triggers the interrupt.

[peterdeco1]

Just a thought. I did something like this for a LDR to act as a motion detector. It should work for a switch.

checkswitch var bit
compare var bit
clear 'bits are 0
low portb.0 'output pin off

start:
let checkswitch = porta.0 'toggle switch
pause 50
let compare = porta.0
if compare <> checkswitch then toggle portb.0 : clear: goto start
goto start

[muddy0409]

I have used the following on a few occasions quite successfully:

Lets say the switch is on portc.3

SW VAR PORTC.3




WHILE SW = 0 : WEND 'THIS WILL CONTINUALLY LOOP AS LONG AS THE INPUT IS LOW, MAKE IT SW = 1 TO DETECT
'GOING LOW.
' ASSUMES THAT ALL YOU ARE DOING IS WAITING FOR A SWITCH CHANGE
'ACCORDING TO THE MANUAL THIS LOOP CHECKS ABOUT 50 TIMES A SECOND
'SO IT SHOULD SEE THE CHANGE WITHIN 1/50 OF A SECOND.

DO SOMETHING HERE 'THIS IS WHAT YOU WANT TO DO AT THE SWITCH CHANGE

[Archangel]

Ok, a JK FlipFlop is a 2 input one output device.
I am guessing you are using a latching relay which
changes states every time it is energised, is
this correct?

If so you need to read 2 pins to check switch state.

@ __config _INTRC_OSC_NOCLKOUT & _WDT_ON & _MCLRE_OFF & _CP_OFF
DEFINE OSC 4
TrisA = %00000011

TRISC = %00000000  
PortC = %00000000

ANSEL=0
ANSELH=0
ADCON0 = 0
ADCON1 = 0
Option_Reg = %00000000 ; enable RABPU
WPUA = %00000011  ;Set RABPU
Main:
If PortA.0 = 0 then 
portc.2 = 1
pause 500  ; 1/2 seconds of power out
portc.2 = 0
else
goto main
endif
goto Impatient  ; wait for microswitch to zero

Impatient:
while PortA.1 = 1
portc.3 = 1
pause 100
portc.3 = 0
pause 100
wend
if PortA.1 = 0 then goto main

end

Tested with 16F690 demo board. Weak pullups did not work, had to use real resistors, likely because the PICKit2 was still connected. LEDs were enabled to verify operation