First a big thank you to Altair Labs for starting this shootout thread. It is a lot of fun, and can only result in better open source products. He has given us at Wicked Device some great suggestions on how to improve our radios, and has been generally all around great to work with.
The first thing that sprung out from the June 7 post is the battery life for the 10 second interval. Each transmission is 0.83 of a second rather than 3 seconds. This should improve it to about 15 days. Still, the proof of the pudding is in the eating, so we did a test (hence the long time in replying). The results are below:
This is consistent with a lifetime of about 15 days. The improvements will be less on the longer interval transmissions, but should still be a couple of days even on the 1 hour interval.
The Node was designed with 2 primary goals:
(1) Under $25 for both sides of the radio link
(2) Overall ease of use.
We also decided to go for a kit. Ease of use includes the whole effort to getting the Node up and running and generating data. Long battery life is a component of this– if your sensor is on your roof, changing the battery every couple of weeks is unusable. One 1 year with a 2200 mAh AA battery pack seemed reasonable.
Reliability of transmission is also important. These little On-Off Keyed radios receive data _all the time_, most of it is just garbage. We think the Node does some pretty nifty stuff, including an error correcting Hamming code and other tricks to generate good data.
Finally, it should just work, with low complexity. Given that this is a kit, which introduces a certain level of complexity, reports are that this solution seems to be pretty easy to use. The software and documentation are a good part of this, but so is being able to remember settings if a reset happens in the field, and the ability to program node ID's without writing code. This is done at startup by shorting ISP pins to ground / 5v. Up to 60 nodes, each with 4 sensors, can be reporting to one receiver, although my guess is that this would be an unlikely use case. 1 - 10 is more likely.
So the DCDW definitely wins on battery life, and on cost, by a whisker. A big congratulations to Altair Labs there, and I don't see any way for a digital/IC based solution to beat that. The Node wins on ease of use and reliability, and is FCC compliant.
How many sensors can the DCDW use, and how many can one receiver handle?