? about sleep/wake on pin change and WDT

I am making a device using the pic10f series microcontrollers whose main purpose is to do a pulsout every couple of seconds. I want it to pulsout and then NAP (go into low power mode between pulses for less than a second to maybe 2 seconds). This is easy.

However, I need to be able to put it to sleep and wake it up on pin change (using a magnetic switch internally sealed from elements) which requires that the WDT be disabled. I am using watch batteries (due to size restrictions) I really need for it to have the lowest power consumption possible AT ALL TIMES. NAP will not work without WDT enabled.

What else can I do, any suggestions?

Use the assembler @ SLEEP option & WDT to wake up periodically and
generate your pulse. Using the prescaler you can have up to 2.3 second
sleep periods.

Use one I/O-pin to wake up on keypress, and another to enter sleep mode
when pressed.

Thanks for your reply but.... Unfortunately I want to be able to just wave the magnet over the switch which will change the pin state and make the pic sleep or wake. I cannot leave the magnet in place on the magnetic switch.

So I need the pic to stay sleeping after an "@ SLEEP" and not to wake at all until the pin changes when the magnet has been waved over the switch.

This means the WDT has to be disabled which kills my "NAP" or "SLEEP" usage and forces me to use pause which will not be the low power usage desired.

Anything else I could try at all?

Is the magnetic switch the "only" thing that will be used to wake it up?

Yes, the magnetic switch will be the ony thing to wake it and tell it to sleep in this application. It should not turn on/off (wake/sleep) until a user turns it or on with the switch..

Here's one scenario;

The PIC wakes up at regular intervals using the WDT. If switch = 0, then go
back to sleep. It's only awake for a few uS testing the switch.

If switch = 1, then do whatever you need to do, then test the switch input
before going back to sleep.

A switch press can also wake the PIC up before a WDT timeout. Handle
whatever you need to do, test the switch, and go back to sleep or stay
awake (resetting WDT) as required, based on the switch input.

It's still going to save a boat-load of power since it will be sleeping until your
switch is active, or the WDT times out.

If the switch isn't active, it's still alseep for the majority of time, and you'll
be operating at low current until the switch input forces the wake up, or the
WDT timeout.

Wouldn't that work?

This could work.... I will try this as soon as I get the chance (prob after the weekend). Thanks for your suggestions, I've been working on multiple projects and they all run together which makes it hard to really focus on the issue at hand enough to get outside the box. Sometimes its just nice to get a fresh perspective on a project.

Thanks again Bruce! I'll post my results when I get back to it next week.

Kessral

If I understand you correctly, you want to do a pulsout (1) every time the PIC is woken by the magnetic switch. Waking on a magnetic switch can be done by a pin change interrupt, if available in the 10F(Havent used, so I cant comment on this). So, your ideal work loop will be something like

while (1)
PULSOUT pin, period
@ SLEEP
@ nop
@ nop
' on waking from interrupt, go back to pulsout
wend

Of course, I haven't shown the part needed to configure the PIC for interrupt on change, etc

Jerson

No Jerson, I'm trying to get it to pulsout as the main function every few seconds or so. I want it to sleep as if it were turned off. And then continue its normal function pulsing when awakened.

I have tried your suggestion tho Bruce and come up with this code:

__________________________________________________ ____________

TRISIO=%11111111
STATUS=%10010000
OPTION_REG=%00001000
check var bit
Low GPIO.0

loop:

nap 4
pulsout 0, 4000
nap 5

IF GPIO.1 = 1 then
suspend:
pause 2000
check = GPIO
sleep 65535
IF GPIO.1 = 1 then
goto loop
else
goto suspend
endif
endif

goto loop
__________________________________________________ _____________

This seems to work. It wakes and sleeps on pin change just fine... however my problem now is that its drawing some 60uA instead of the 5-10uA listed in the datasheet. I'll keep looking through to see if there is something else I can do to lower the current drain, but for now this seems to be as close as I am going to get.

I DID notice however that GPIO 3 is constantly high... this could have something to do with current drain being slightly higher so that is what I am currently looking into.

Again thanks for the Input guys.

P.S. This is on a PIC10F202 and I am using MPLAB IDE v7.11

Quote:

---

Originally Posted by kessral

No Jerson, I'm trying to get it to pulsout as the main function every few seconds or so. I want it to sleep as if it were turned off. And then continue its normal function pulsing when awakened.

I have tried your suggestion tho Bruce and come up with this code:

__________________________________________________ ____________

TRISIO=%11111111
STATUS=%10010000
OPTION_REG=%00001000
check var bit
Low GPIO.0

loop:

nap 4
pulsout 0, 4000
nap 5

IF GPIO.1 = 1 then
suspend:
pause 2000
check = GPIO
sleep 65535
IF GPIO.1 = 1 then
goto loop
else
goto suspend
endif
endif

goto loop
__________________________________________________ _____________

This seems to work. It wakes and sleeps on pin change just fine... however my problem now is that its drawing some 60uA instead of the 5-10uA listed in the datasheet. I'll keep looking through to see if there is something else I can do to lower the current drain, but for now this seems to be as close as I am going to get.

I DID notice however that GPIO 3 is constantly high... this could have something to do with current drain being slightly higher so that is what I am currently looking into.

Again thanks for the Input guys.

P.S. This is on a PIC10F202 and I am using MPLAB IDE v7.11

---

Have you got any pullup or pulldown resistors in there anywhere?
5v / 10k = 500uA
And the datasheet does say that the weak pull up current is 250uA average.
Just a couple of ideas for ya...

This is a good point. And I did think of this. Currently I have 1 15k pulldown to ground from the pin connected to magnetic switch to help determine high/low state.

However 60uA is not consistent with this.. I'll just have to keep it in the back of my mind, as I have many other things to get to as well, maybe I'll think of something.

Try this;

Code:

---

DEFINE OSC 4
   
    ' GPIO.1 & 3 inputs, rest outputs. Use external pull-ups
    ' on GPIO.1 & 3.
    TRISIO=%00001010
    ' Internal pull-ups off, prescaler to wdt, 1:128 prescale,
    ' wakes up approx every 2.3 seconds.
    OPTION_REG=%01001111

    Low GPIO.0 ' pre-condition output for high pulsout

Loop: ' 100K external pull-up on GPIO.1, switch grounds GPIO.1
      ' when pressed
    WHILE GPIO.1 = 0    ' if button pressed, do pulsout
      CLEARWDT        ' reset WDT while in loop
      pulsout 0, 4000  ' pulsout GPIO.0
    WEND
   
    ' Note: It will wakeup about every 2.3 seconds on WDT timeout,
    ' or switch press, but doesn't pulsout unless switch is pressed.   
    @ SLEEP            ; else sleep
    ' Don't need goto here since wake up is a device reset.
    END

---

just use a inline resistor and a cap to GND on the output of your switch.

V+ --- [resistor, 10K?]----[reed switch]----[Capacitor from this line to GND]----pic I/O

The cap will "store" the switch closure event so that when the unit wakes up it can tell the reed switch was closed while it was sleeping.

The PIC can then, once it wakes up, flip the input bit to a grounded output to "reset" the circuit. Then just before SLEEP it can make the pin back into an input.

Note that if the circuit board is damp or dirty and you don't reset the circuit on every wake up from sleep, that eventually the cap can charge up.

The cap can be very small, 0.01uF (10nF) would work just fine. I tried to make
a proper ascii schematic but this forum has no code mode that I can see.