I know it wouldn’t be programmable without editing bootloaders etc - but if I programmed a chip with the usual 16MHz setup, then removed the crystal/supporting caps, and changed it to a 32kHz one - would it run ok(obviously at 1/500th of the original speed so delay(etc) would all be wrong time values) and would it lead to any running problems?
Thanks all!
They can be boot/fuse loaded into very slow speeds (they come from the factory at 250khz) but i’m not sure they can go to 32khz.
for slower speeds, the chips have an internal clock and divider so no need for an external xtal
What’s the idea that needs such slow speeds ?
Courty
I got curious, I found these links which do discuss the issue, but do not sound too hopeful that running the cpu clock at 32 khz as being practical.
https://www.davidpilling.com/wiki/index.php/Arduino32768
http://www.home-automation-community.com/arduino-low-power-how-to-run-atmega328p-for-a-year-on-coin-cell-battery/
http://www.atmel.com/images/doc8333.pdf
if your looking for long life battery operation, ive had success with low power 3.3v 8MHz AVR parts, paired with the low power libraries and LDO 3.3v voltage regulators with low quiescent currents.
the power lost with the higher clock speed can be more than offset by the power savings from the cpu spending more time in deep sleep, because it finishes its tasks quicker
If you are interested in low power have a look at pic as they can stop dead and power drops to zero.
Effectively a clock of 0hZ until woken up by a interrupt
Arduino chips (atmel 328p) can be run in the micro amp standby modes if your app allows for sleep periods and you don’t use the standard Arduino boards. I did some morse thermometers a while back that ran on 2 x AAA batts for months.
The ESP8266 can go to almost zero and as @joeatkin2 says PICs do a full halt in sleep. Sleep/halt is the key to low power for sure.
If you have an app that requires low power running without sleeps, you’re into some specialist chips.
Courty
Basically a type of clock that sleeps most of the time then on interrupt does some lighting sequences then goes back to sleep - in as small an overall setup as possible, including battery, so low power requirements.
Nick Gammon had a lot of useful stuff on it - https://www.gammon.com.au/forum/?id=11497
However, I misread/misunderstood the watchdog timer - I knew it was a limit of 8 seconds but thought it was related to the clock freq - and thus reducing it would increase the length of watchdog timer (and thus could sleep it for ages). But it turns out on further reading the watchdog timer is independant, and worse, not very accurate… Thus foiling my plans to do everything on one chip.
Reading further, I reckon best is probably an RTC (which I’m not familiar with, but stuff like Maxim DS1337+ looks good) and an atmega chip - unless anyone has any cleverer ideas?
@joeatkin2 The pic no power until interrupt is very cool! Will bare that in mine, cheers!
Thanks all and always interested to hear more thoughts!
Take a look at the U variant of the Atmega , they can operate a 1.8v