Computing stuff tied to the physical world

One million packets

In AVR, Hardware, Software on Sep 15, 2012 at 00:01

Minutes after this weblog post goes live will be a new milestone for one of the JeeNodes.

This thing has been running for over two years, sending out nearly one million test packets:

Here are the entries from the data logged to file on my central server, minutes ago:

1:40   RF12-868.5.3 radioBlip age       740
1:40   RF12-868.5.3 radioBlip ping      999970

The counter is about to reach 1,000,000 – just after midnight today, in fact.

These log entries come from a JeeNode with a radioBlip sketch which just sends out a counter, roughly every 64 seconds, and goes into maximum low-power mode in between each transmission. That’s the whole trick to achieving very long battery lifetimes: do what ya’ gotta do as quickly as possible, then go go bck to ultra-low power as deeply as possible.

The battery is a 1300 mAh LiPo battery, made for some Fujitsu camera. I picked it because of the nice match with the JeeNode footprint.

Bit the big news is that this battery has not been recharged since August 21st, 2010!

Which goes to show that:

  • lithium batteries can hold a lot of charge, for a long time
  • JeeNodes can survive a long time, when programmed in the right way
  • sending out a quick packet does not really take much energy – on average!
  • all of this can easily be replicated, the design and the code are fully open source

And it also clearly shows that this sort of lifetime testing is really not very practical – you have to wait over two years before being sure that the design is as ultra-low power as it wast intended to be!

If we (somewhat arbitrarily) assume that the battery is nearly empty now, then running for 740 days (i.e. 17,760 hours) means that the average current draw is about 73 µA, including the battery’s self-discharge. Which – come to think of it – isn’t even that low. I suspect that with today’s knowledge, I could probably set up a node which runs at least 5 years on this kind of battery. Oh well, there’s not much point trying to actually prove it in real time…

One of the omissions in the original radioBlip code was that only a counter is being sent out, but no indication at all of the remaining battery charge. So right now I have no idea how much longer this setup will last.

As you may recall, I implemented a more elaborate radioBlip2 sketch a while ago. It reports two additional values: the voltage just before and after sending out a packet over wireless. This gives an indication of the remaining charge and also gives some idea how much effect all those brief transmission power blips have on the battery voltage. This matters, because in the end a node is very likely to die during a packet transmission, while the radio module drains the battery to such a point that the circuit ceases to work properly.

Next time, as a more practical way of testing, I’ll probably increase the packet rate to once every second – reducing the test period by a factor of 60 over real-world use.

Waiting a couple of years for the outcome is a bit silly, after all…

  1. Congratulations on you 1 millionth… is there a difference in powerconsumption between an SMD Jeenode and a regular one?

    • I don’t believe so Peter. They are the same version of the 328 just in a different package.

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