[leppie]

Author misinterpreted specs...

"Each packet has 20 bytes of useful payload and consumes 49 μA at 3 V"

That is a manufacture average for some profile, mostly sleeping 99% of the time.

The real consumption during broadcast is in the order of 15-20mA for most chip I have seen.

Here is a very informative article dealing with power demands of low power devices: www.ganssle.com/reports/ultra-low-power-design.html

[MootWoop]

Thanks for the link, indeed it looks quite technical and very complete on the subject. Truth be told I'm far from an expert on power, hence the mistake :-)

[Gurkenmaster]

Considering the 1 minute interval wouldn't it be better for the battery to use a clock implemented in hardware that boots the chip everytime it's needed?

[unwind]

That is typically what you do, microcontrollers have timers and low-power mode(s) which keep the timers running even though the processor core isn't executing any instructions.

[MootWoop]

I'm not an expert on power optimization, and I don't know how this is done in micro-controllers. But I would think that the hardware clock would be implemented using integrated analog components (capacitor + resistor circuit) rather than digital logic, to avoid repeatedly switching on and off even just a few transistors.

[BostonEnginerd]

The power needed to keep the analog comparator going will probably be higher than keeping the 32kHz clock running.

[pjc50]

Apparently external xtal is marginally best (http://www.microchip.com/forums/m341592.aspx); which makes intuitive sense, given that it's exactly the same scenario as a digital watch. 32khz crystal; driver; counter; comparator. Few hundred tiny transistors. Consumption probably less than battery self-discharge.