Accurate hourly interupt for PIC

G

Glenn Pure

Guest
Advice wanted please on a suitable source of interupt for a
micrcontroller that meets the following:

1. Low current consumption (will run for at least 6 months on minimal
battery power)

2. Accurate (to within a few minutes a month)

3. Signal for interupt needed every hour (but could cope with other
intervals, eg evey minute or 10 minutes).

I want to build an unattended microcontroller circuit that will run
from a 6 volt lantern battery or smaller for at least 6 months. Hence,
I'm assuming that a crystal oscillator and clock implemented in
software on the microcontroller won't work for me this time due to
current consumption. I suspect I will need to sleep the
microcontroller (and hence shut down its oscillator) to minimise
current consumption....

however, if I'm wrong on this and there is an accurate low current
oscillator option that will run a PIC, I'd love to hear about that
too.

Cheers
Glenn
Glenn Pure
Canberra, Australia
Web page: http://www.evans-pure.net
 
On 2006-02-19, Glenn Pure <glenn*delete_this_for_reply*@evans-pure.net> wrote:
Advice wanted please on a suitable source of interupt for a
micrcontroller that meets the following:

1. Low current consumption (will run for at least 6 months on minimal
battery power)

2. Accurate (to within a few minutes a month)

3. Signal for interupt needed every hour (but could cope with other
intervals, eg evey minute or 10 minutes).
Click to expand...
a "two dollar" watch will do that
get one capabile of producing a short tone every hour,
and connect the output to an amplifier

I want to build an unattended microcontroller circuit that will run
from a 6 volt lantern battery or smaller for at least 6 months. Hence,
I'm assuming that a crystal oscillator and clock implemented in
software on the microcontroller won't work for me this time due to
current consumption. I suspect I will need to sleep the
microcontroller (and hence shut down its oscillator) to minimise
current consumption....

however, if I'm wrong on this and there is an accurate low current
oscillator option that will run a PIC, I'd love to hear about that
too.
Click to expand...
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

"Anthony Fremont" <spam@anywhere.com> wrote:

"Glenn Pure" <glenn*delete_this_for_reply*@evans-pure.net> wrote in
message news:75igv1d93emvclu789i9ih9jfe3psj738a@4ax.com...
Advice wanted please on a suitable source of interupt for a
micrcontroller that meets the following:

1. Low current consumption (will run for at least 6 months on minimal
battery power)

Any nanowatt PIC should do.

2. Accurate (to within a few minutes a month)

Use a watch crystal to run it.

3. Signal for interupt needed every hour (but could cope with other
intervals, eg evey minute or 10 minutes).

I want to build an unattended microcontroller circuit that will run
from a 6 volt lantern battery or smaller for at least 6 months. Hence,
I'm assuming that a crystal oscillator and clock implemented in
software on the microcontroller won't work for me this time due to
current consumption. I suspect I will need to sleep the
microcontroller (and hence shut down its oscillator) to minimise
current consumption....

however, if I'm wrong on this and there is an accurate low current
oscillator option that will run a PIC, I'd love to hear about that
too.

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.
Glenn Pure
Click to expand...
Canberra, Australia
Web page: http://www.evans-pure.net
 
"Glenn Pure" wrote:

Please don't top post.

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.
Click to expand...
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.
 
"David L. Jones" <altzone@gmail.com> wrote:

Glenn Pure wrote:
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.

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.
Click to expand...
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?

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 :)
Glenn Pure
Click to expand...
Canberra, Australia
Web page: http://www.evans-pure.net
 
"Glenn Pure" <glenn*delete_this_for_reply*@evans-pure.net> wrote in message
news:75igv1d93emvclu789i9ih9jfe3psj738a@4ax.com...
I want to build an unattended microcontroller circuit that will run
from a 6 volt lantern battery or smaller for at least 6 months. Hence,
I'm assuming that a crystal oscillator and clock implemented in
software on the microcontroller won't work for me this time due to
current consumption. I suspect I will need to sleep the
microcontroller (and hence shut down its oscillator) to minimise
current consumption....
Click to expand...
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
 
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