Post by thread:In and Out of Sleep

I looked through the archives but couldn't find what I needed. Any help on this would be appreciated. I want to put a PIC16C715 to sleep in the middle of a loop. I want it to go to sleep for 2.5 seconds, give or take couple tenths, and automatically start back up where it left off. I also need to be able to wake it up as the result of a digital input being asserted. Battery current draw has become a significant factor in this project. I was going through a loop 50 times, checking for the digital input each time, in order to get my 2.5 second delay. It looks like I can reduce my current draw significantly by implementing the SLEEP function, but being a beginner, I don't know how to do it. Thanks. Mark Peterson

Mark Peterson wrote: > I looked through the archives but couldn't find what I needed. Any help on > this would be appreciated. > > I want to put a PIC16C715 to sleep in the middle of a loop. I want it to > go to sleep for 2.5 seconds, give or take couple tenths, and automatically > start back up where it left off. I also need to be able to wake it up as > the result of a digital input being asserted. > > Battery current draw has become a significant factor in this project. I > was going through a loop 50 times, checking for the digital input each > time, in order to get my 2.5 second delay. It looks like I can reduce my > current draw significantly by implementing the SLEEP function, but being a > beginner, I don't know how to do it. If you aren't too concerned about accuracy, use a TLC555 timer to wake up the processor with the INT pin at your sampling rate. You'll need a big capacitor and good circuit layout to get that long a basic period. There is also a 555 based device with built in counter chain for 'long period timing', but I don't remember the part # off hand. If you want better stability, use a 4060 with a 32kHz xtal osc and tap off Q13 to get a .5 hz interrupt rate and divide in software to get 2.5 seconds. (Or use 1Hz tap and use software to interrupt on the opposite edge after the 2nd one (1 sec + 1 sec + .5 sec). You could also use a Dallas D1307 and the 1Hz SQWO to interrupt. Use a B7:4 bit to 'wake on change' for your other pin, or wire or your input to INT. Lots of choices now... spam_OUTRobert.RolfTakeThisOuTUAlberta.ca

When you put a PIC into SLEEP mode, its oscillator stops, which stops almost all of its internal logic. This is what makes it draw so little current (a couple of microamps). It also means that most of the stuff inside the PIC stops working, including counters that are running off the oscillator. So you will need some kind of external timing source. You could use some sort of counter or one-shot to provide a wake-up pulse on the RB0/INT pin, which will wake most of the PIC's, or there are other pins on various models, which can be used to wake up the processor. The mid-range PIC's (I'm using 16C63A, mostly) have a TIMER1, which can be configured to run in sleep mode using a 32KHz watch crystal. This can be quite simple (though a tiny bit tricky to get the oscillator right see App note 588, which you can get from the Microchip website), and can get you sleeping with a convenient software-settable wake-up timer for about 20 microamps. > {Original Message removed}

Something else to think about is using the WDT to wake you from sleep. I forget the accuracy specs on the WDT reset, but I know it can be scaled with Timer0 to about 2.5s. If you need more accurate time than its RC oscillator provides, you can use your crystal to calibrate periodically. I do this on a project by setting a flag and letting my micro watchdog out. While I'm waiting for the watchdog timeout I increment a counter. The flag setting tells me I did an intentional dog out and I go to code that reads the counter and adjusts my sleep times accordingly. HTH Erik Reikes At 03:52 PM 1/31/00 -0600, Don Hyde wrote: {Quote hidden}>When you put a PIC into SLEEP mode, its oscillator stops, which stops almost >all of its internal logic. This is what makes it draw so little current (a >couple of microamps). It also means that most of the stuff inside the PIC >stops working, including counters that are running off the oscillator. > >So you will need some kind of external timing source. > >You could use some sort of counter or one-shot to provide a wake-up pulse on >the RB0/INT pin, which will wake most of the PIC's, or there are other pins >on various models, which can be used to wake up the processor. > >The mid-range PIC's (I'm using 16C63A, mostly) have a TIMER1, which can be >configured to run in sleep mode using a 32KHz watch crystal. This can be >quite simple (though a tiny bit tricky to get the oscillator right see App >note 588, which you can get from the Microchip website), and can get you >sleeping with a convenient software-settable wake-up timer for about 20 >microamps. > > >> {Original Message removed}

On Mon, 31 Jan 2000 15:51:29 -0800 Erik Reikes <.....ereikesKILLspam@spam@XSILOGY.COM> writes: > Something else to think about is using the WDT to wake you from > sleep. I > forget the accuracy specs on the WDT reset, but I know it can be > scaled > with Timer0 to about 2.5s. Yep, I've done this. The PIC wakes up on a WDT timeout or interrupt. It the continues from where you "put it to sleep". Harold ________________________________________________________________ YOU'RE PAYING TOO MUCH FOR THE INTERNET! Juno now offers FREE Internet Access! Try it today - there's no risk! For your FREE software, visit: dl.http://www.juno.com/get/tagj.

>Date: Tue, 1 Feb 2000 12:36:28 +1300 >From: Andrew Hooper <andrewKILLspamBEST.NET.NZ> >Subject: Re: In and Out of Sleep > >Rather than use a 555 timer why not use an LM3909? >if I remember correctly they use less power than thee 555 >and will opperate from a wide range of voltages. The LM3909 was discontinued about 18 months ago. regards, Peter Crowcroft DIY Electronics (HK) Ltd PO Box 88458, Sham Shui Po, Hong Kong Voice: 852-2720 0255 Fax: 852-2725 0610 Email: .....peterKILLspam.....kitsrus.com Web: http://kitsrus.com ----------------------------------------------------------------------

Peter or KITSRUS wrote: > The LM3909 was discontinued about 18 months ago. And a good thing too. A highly over-hyped chip in the hobby literature IMO. Its time-constant resistor was about 3 k ohm, so it required *very* large capacitors for slow flash rates and even this resistance represented a minimum drain of about 1 mA. Also, and related to that resistance, it wasn't particularly useful for all the other applications suggested (given that its primary application was to flash a LED from a 1.5 V cell). If you were to use a 555, it would be a TLC555. But all this is unnecessary complication. The best answer to the question was that you use the Watchdog timer - that appears to be what it was put there for. -- Cheers, Paul B.