On 13/10/2023 16:03, John wrote:
The Natural Philosopher <tnp@invalid.invalid> writes:
A nice evolution of the Pi.
I would rather see a Pi that will run for 7 days from 4xAA.
I am building one that I hope will run for a year from 3xAA
A truly impressive goal, given that some of the more seriously power-efficient microcontrollers I can find draw 2.4mA when in
operation, which would give you about 145 days of runtime on 3 2850mAh alkaline AA batteries. They claim that power consumption scales with
clock rate, so if you halved the clock rate to 16MHz you'd get almost a
year.
Interested to hear your plans.
Oh its very simple. I tried to do it old school with an analogue timer
but couldn't get it done simply due to unavailability of low leakage
large value capacitors so I looked at uber low current draw timers, but
they were all surface mount and I cant do that technology due to old
eyes and fingers, but I found a board that does exactly what I want made
by sparkfun
https://www.sparkfun.com/products/15353
With that surface mount timer chip on it.
The theory is the timer times out, the pico wakes up, measures oil level
with a burst of ultrasonics. checks the battery level, connects to my
wifi, shoves a small TCP/IP packet to the pi zero server and once it
gets an 'Ack' flips a GPIO pin which goes to the timer board and shuts
down the pico for an hour or so.
I reckon a minute an hour of about 100mA consumption so an average draw
of around 1.6mA times 24x365 is 14Ah. Which isn't great, so I am hoping
that it can read data and connect/send in less time than that . The big
problem is the oil tank is remote and the existing wireless device
can't do the range to a sensible place for the receiver, but I can put a
wifi hotspot *almost* close enough. And up high if needs be.
It wouldn't be the end of the world if it just connected every 3-4 hours
or every day - oil levels move slowly, but the largest preset delay the chipset will do is 2 hours.
The main issue the pico has is sending wifi data, where it can spike (allegedly) to 150mA, but while running its not much more than 50mA. But
then the ultrasonic transducer will take a bit to do its 'chirp'. So
its all very unknown.
The current device often takes a day to respond to a recently filled
tank. It runs off a 2032 lithium battery I think, button cell anyway.
That lasts about 18 months
So its all a bit 'how long will the battery last' until I've built it,
and that's why the voltage monitor is going in. I will probably set the
server up to send me an email on either low battery or low oil!
I don't mind changing batteries twice a year if I have to, as long as I
can do it before winter sets in!
john
--
"When a true genius appears in the world, you may know him by this sign,
that the dunces are all in confederacy against him."
Jonathan Swift.
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