Accurate hourly interupt for PIC

Are you fixed on using a pic? The msp430 series from ti are very low power, and have an optional internal oscillator. It also has several versatile timers that can generate interrupts. The TI website has examples of using the internal timers as a RTC.

The PIC10F204 is a 6 pin (sot-23) 100nA sleep current micro.

Many PICs (or almost any other micro) can meet all your specs with a

32KHz watch crystal which runs continuously and you use a timer to interrupt and wake up the CPU at the pre-set time interval. If you don't need fast processing then use the 32KHz clock to do your processing too, and you may not even need to switch to sleep mode depending on your battery size. Otherwise have a faster 4MHz internal oscillator switch on at the interrupt, do any processing needed and then shut down again. This is all PIC-101 stuff and is explained in many app notes etc.

Dave :)

Any nanowatt PIC should do.

Use a watch crystal to run it.

A PIC 12F683 uses something like 18uA typical running at 32kHz on 3V and only 9uA typical at 2V. As long as you can live without the BOD (brownout) and WDT (watchdog) that should be it on the current requirements without sleeping. Sleeping and using a watch crystal connected to T1OSC could save you maybe 50% off that on the power. Probably not really worth the extra effort, unless you want to be able to wake up and crank the CPU speed up to 8MHz.

A lantern battery won't be necessary, a couple of AA batteries should easily last for years even running continuously.

a "two dollar" watch will do that get one capabile of producing a short tone every hour, and connect the output to an amplifier

Atmel has an application note on their site (or possibly in the datasheet) where they loop one of the AT90S2313 counters into the external input for the other to build a 24-bit counter. with a 32768 Hz crystal and a 2.7V supply the current draw is below 100uA,

there's a trick using the watchdog timer that'll let you shut the chip down (where current consumption is about 5uA with a 2.7v supply the watchdog timer is temperature compensated, and should run at a predicttable rate.

another option would be a "cmos clock" from a PC the older ones had an 8-bit parallel interface and were capable of producing an alarm signal at a programmed time (you'd need to set the alarm for 60 minutes into the future) but that may to tie up lots of your IO pins

I'd expect over 1 year from a few alkaline AA batteries for that part

unfortunately none of those suggestions will run directly off a 6V lantern battery.

Bye. Jasen

Thanks to posters for advice. I don't need any processing grunt. A

32KHz crystal would be fine for me needs.

BTW, I will need to use a PIC with an A/D converter so am somewhat limited in my choices.

Cheers Glenn

"Anth>

Glenn Pure Canberra, Australia Web page:

Please don't top post.

How many I/O pins do you need? The 12F683 has a max of 6 I/O pins, and the 16F88 has a max of 16 I/O pins. Both have multiple channels of ADC.

A/D converters aren't the only way to measure voltage.

Bye. Jasen

Listing all the "nanoWatt" pics with ADCs on the Microchip website shows that you have no real shortage of choice. If pin count is not a problem then the 16F88 would probably be the first choice as it is readily available. You probably don't need a nanoWatt device either, do the power calculations for a clock speed of 32.768KHz on a normal PIC and you might find that will be OK for your requirements too. BTW, with a clock speed this low you will need to choose the internal RC oscillator for the ADC clock source, as the clock needs to be within a specific range.

Dave :)

It would seem the 16LF88 rather than the 16F88 is needed? The data sheet suggests the 16F88 isn't rated below 4.0V. Anyone done the experiment?

If I'll need the 16LF88, any suggestions where to obtain it?

Glenn Pure Canberra, Australia Web page:

Running a micro off a lantern battery for 6 months isn't a huge ask, some micros will run off a watch battery for years. Although they are probably less powerful you shouldn't have much trouble getting this to run for close to the shelf life of the battery :-)

Michael

Only if you want to power it from less than 4V What's worng with 3 or 4 series AA cells?

It will most likely work, but you won't be able to count on it. Probably just some spec margin thing. I've heard of people using them below that without problem.

Farnell & RS have plenty of LF PICs in other ranges, but not the LF88 I don't think. The 16LF877A would be suitable, if you don't mind the 40pin package.

Dave :)