Post by thread:[PIC]: Sleep power & wake-up

Hi, I've got a puzzle involving a 12CE674, but applicable to most PICs. I want to put the PIC to sleep drawing as little power as possible, and wake up on a pin change. I can turn on the internal weak pull-ups, enable interrupt in pin change, go to sleep, ground a pin, everything works great. Unfortunately, the current draw is about 700uA with my JW test mule! This thing will sit for weeks at a time (maybe longer) on 2 or 3 AA bateries, and I don't want it killing the batteries while it's asleep. Yes, I have WDT and the ADC off and everything, it's just the weak pullups that are sucking electrons, I turn off internal pullups and current drops WAY down. So I figure maybe I can make the pins outputs, drive 'em high and a momentary ground will wake them up, since the interrupt on change looks at the pin "past" the output drivers -- no joy, of course (yeah, I know it was a dumb idea). The good news is, sleep current is close to zero. Bad news is, grounding the pin causes 23mA current draw but no wakeup. I'd like to do this without using an external pullup resistor if at all possible, but it's not looking too good right now. Any more ideas? Dale -- "Curiosity is the very basis of education and if you tell me that curiosity killed the cat, I say only the cat died nobly." - Arnold Edinborough -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

At 04:16 PM 3/9/02 -0600, Dale Botkin wrote: >Hi, > >I've got a puzzle involving a 12CE674, but applicable to most PICs. I >want to put the PIC to sleep drawing as little power as possible, and wake >up on a pin change. I can turn on the internal weak pull-ups, enable >interrupt in pin change, go to sleep, ground a pin, everything works >great. Unfortunately, the current draw is about 700uA with my JW test >mule! This thing will sit for weeks at a time (maybe longer) on 2 or 3 AA >bateries, and I don't want it killing the batteries while it's asleep. >Yes, I have WDT and the ADC off and everything, it's just the weak pullups >that are sucking electrons, I turn off internal pullups and current drops >WAY down. Did you cover the window? Try adding high value pull-up resistors 1 at at time to the pins while monitoring the supply current while in sleep. Are you sure the internal pull-ups are enabled? Use a really high impedance meter to measure the pin voltage or use a DMM but measure from the pin to both VDD and GND (all the while looking at the supply current). Look for leakage paths: what you are seeing could be the result of sneak leakage currents bringing the pin voltage part way down from VDD and thus into the linear region. Adding strong pull-ups one at a time to the pins while monitoring supply current will help identify this. Did you disable BOD? You should be able to get down to less than 20 uA - I have done so with the 12ce673. dwayne Dwayne Reid <spam_OUTdwaynerTakeThisOuTplanet.eon.net> Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 18 years of Engineering Innovation (1984 - 2002) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Why not just use an external pullup? You are right about the internal pullups drawing too much. David On Sat, 9 Mar 2002 16:16:32 -0600 Dale Botkin <.....daleKILLspam@spam@BOTKIN.ORG> wrote: {Quote hidden}> Hi, > > I've got a puzzle involving a 12CE674, but applicable to most PICs. I > want to put the PIC to sleep drawing as little power as possible, and wake > up on a pin change. I can turn on the internal weak pull-ups, enable > interrupt in pin change, go to sleep, ground a pin, everything works > great. Unfortunately, the current draw is about 700uA with my JW test > mule! This thing will sit for weeks at a time (maybe longer) on 2 or 3 AA > bateries, and I don't want it killing the batteries while it's asleep. > Yes, I have WDT and the ADC off and everything, it's just the weak pullups > that are sucking electrons, I turn off internal pullups and current drops > WAY down. > > So I figure maybe I can make the pins outputs, drive 'em high and a > momentary ground will wake them up, since the interrupt on change looks at > the pin "past" the output drivers -- no joy, of course (yeah, I know it > was a dumb idea). The good news is, sleep current is close to zero. Bad > news is, grounding the pin causes 23mA current draw but no wakeup. > > I'd like to do this without using an external pullup resistor if at all > possible, but it's not looking too good right now. Any more ideas? > > Dale > -- > "Curiosity is the very basis of education and if you tell me that > curiosity killed the cat, I say only the cat died nobly." > - Arnold Edinborough -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On Sat, 9 Mar 2002, David Koski wrote: > Why not just use an external pullup? You are right about the internal pullups > drawing too much. At this point it's just trying to figure out what I'm not doing right. The resistors aren't that big a deal, I just want to see if I can get the parts count down to an absolute minumum. Dale -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On Sat, 9 Mar 2002, Dwayne Reid wrote: > Did you cover the window? Yep. > Try adding high value pull-up resistors 1 at at time to the pins while > monitoring the supply current while in sleep. Are you sure the > internal pull-ups are enabled? Yep. > Use a really high impedance meter to measure the pin voltage or use a > DMM but measure from the pin to both VDD and GND (all the while > looking at the supply current). Look for leakage paths: what you are > seeing could be the result of sneak leakage currents bringing the pin > voltage part way down from VDD and thus into the linear region. > Adding strong pull-ups one at a time to the pins while monitoring > supply current will help identify this. Ain't nuthin' there to do it. GP0 & 1 are open switch inputs, GP2 is set to output and driven low to an LED & resistor to GND. GP3-5 are open, set as outputs and driven low. I can leave all the pins open, same result. > Did you disable BOD? I would have if the 12CE67x had BOD ;) > You should be able to get down to less than 20 uA - I have done so with the > 12ce673. I think I just got it there. Made a code change to drive GP1 as a low output and leave GP0 as an input, and the sleep current dropped like a rock. Reads 0.00 on my Fluke 77 meter, which means it's low enough. I have to wonder if my well-used 12CE673-JW had a flaky output drive on GP1. I also think it may have been waking up as soon as it went to sleep but not sure -- if it was it should have given me an indication by turning an output on, which it didn't, but the 700uA is suspiciously close to what it draws with all the outputs disconnected and the PIC not sleeping. At any rate, it seems to be working as expected now with sleep current too low to measure with my meter, so all's well! 8-) Dale -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> I've got a puzzle involving a 12CE674, but applicable to most PICs. I > want to put the PIC to sleep drawing as little power as possible, and wake > up on a pin change. I can turn on the internal weak pull-ups, enable > interrupt in pin change, go to sleep, ground a pin, everything works > great. Unfortunately, the current draw is about 700uA with my JW test > mule! This thing will sit for weeks at a time (maybe longer) on 2 or 3 AA > bateries, and I don't want it killing the batteries while it's asleep. > Yes, I have WDT and the ADC off and everything, it's just the weak pullups > that are sucking electrons, I turn off internal pullups and current drops > WAY down. Something doesn't sound right. The weak pullups shouldn't be drawing much current as long at the external circuit lets the lines float high. Are one or more of the port B pins held low during sleep? ******************************************************************** Olin Lathrop, embedded systems consultant in Littleton Massachusetts (978) 742-9014, olinKILLspamembedinc.com, http://www.embedinc.com -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On Sat, 9 Mar 2002 17:04:58 -0600 Dale Botkin <.....daleKILLspam.....BOTKIN.ORG> wrote: > On Sat, 9 Mar 2002, David Koski wrote: > > > Why not just use an external pullup? You are right about the internal pullups > > drawing too much. > > At this point it's just trying to figure out what I'm not doing right. > The resistors aren't that big a deal, I just want to see if I can get the > parts count down to an absolute minumum. I might be missing something but I don't see how you will beat your original idea with only using external pullups instead. It is unfortunate that the internals suck so much power. Is a contact switch driving the input? David -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

I would like to know if anyone has actually accomplished reasonable power drain using internal pullups, how much power was consumed, and how it was accomplished. David Koski EraseMEdavidspam_OUTTakeThisOuTKosmosIsland.com On Sat, 9 Mar 2002 18:50:28 -0800 Bob Ammerman <rammermanspam_OUTADELPHIA.NET> wrote: {Quote hidden}> Dale, > > Turning on the internal pullups should _not_ result in such a jump in > current draw, unless one or more of the pins is connected via a not very > large resistance to ground. > > Is one of the other pins, beside the one you are trying to use for wakeup, > pulling a pin down? > > Bob Ammerman > RAm Systems > > {Original Message removed}

On Sat, 9 Mar 2002, Bob Ammerman wrote: > Turning on the internal pullups should _not_ result in such a jump in > current draw, unless one or more of the pins is connected via a not very > large resistance to ground. Well, the data sheet says max 400uA. It doesn't specifically say total or per pin. Even 400uA is a little more than I'd like to see, though. We're talking about AA batteries, and I'd like to not see them drained. Yeah, sure, I *could* just add a SPST slide power switch, but where's the fun in that? Heck, that'd be like switching AC with a relay! 8-D I guess it's kind of an academic exercise, really. This is a one-off, but I'm lookig at it from a commercial perspective to see how low I could get the per-unit cost in production and still have it operate reliably. Old habits die hard, I guess. Not just parts cost, but board space and assembly cost too... the ideal design is one component. I've got this one down to one PIC, one resistor, one NPN transistor and an optional (but recommended) cap. > Is one of the other pins, beside the one you are trying to use for wakeup, > pulling a pin down? I suspect my GP1 pin is flaky on the -JW part I have. When I set it as a HI output and leave GP1 as an open input the current consumption in sleep mode goes WAY, WAY down. Below where my meter can read it, which is low enough for me. I may have to break down and replace my EPROM chip. It's spent enough time in the eraser it's got a nice tan though! ;) Dale -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

On Sat, 9 Mar 2002, David Koski wrote: > I would like to know if anyone has actually accomplished reasonable power drain > using internal pullups, how much power was consumed, and how it was > accomplished. Depends on what you call "reasonable". If I had a better meter I could tell you what mine's at now, but it meets my criteria for reasonable. Datasheet says typical supply current is .4 to 2.1mA max with INTRC (which I'm using) at 2.5Vdd (I'm at about 4-4.5V). When awake but idling, no loads connected, my Fluke says 700uA. When it goes to sleep, data sheet says .2 to 5 uA, my meter says 0.00 - meaning it's below 10uA, anyway. Dale -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

Dale, To read really, really, low sleep currents this is what I do: 1. Put a 1K resistor in series with the power supply, and connect a multimeter in voltage mode across it. 2. Clip a jumper on to short out the 1K resistor 3. Turn on power and get the unit into sleep mode. 4. Remove the jumper across the 1K resistor. 5. Now you can read the current on the meter scalled at 1 mv per uA. [you can use a 10K R to get 10x the resolution, but then the scaling is 10mv per uA] Bob Ammerman RAm Systems {Original Message removed}