Long life powering of remote Xbee

  1. I am working on a wireless sensor application at my internship. The sensor network is working, and I am using two Xbee radios, one at the sensing end and the other at the receiving end which routes the information into a central MCU.
    The issue is, the sensing radio needs to be standalone and thus will run off of a battery. As of right now, we are seeing about 30-40mA being drawn from the circuit, running off of a 5V power supply that I am acquiring from an Arduino for prototyping convenience. The device needs to be able to operate alone for a long period of time, as we would rather not force our clients to change the battery every couple of weeks.
    I have very little knowledge of battery options out there. My question is, what is the best way to power a remote sensing circuit and allow for minimal power consumption so that it may be powered for as long as possible?
  2. jcsd
  3. berkeman

    Staff: Mentor

    Welcome to the PF.

    One approach is to "sleep" your sensor circuit for the majority of the time, and only "wake up" to do the sensing and transmit the data for a very short time. This works well if the data are not changing very quickly. What is your sleep current? Can you design the circuit to be off or asleep most of the time? What would be the wake-up time?

    To do this, you use a micropower oscillator/counter, which trips the wake-up signal or powers up the circuit. I've built such a circuit that only draws about 1uA, which lets a small radio sensor device last for about a year on two AA batteries...

    You can also Google micropower circuits to learn more... :smile:
  4. I am currently researching sleep modes for the Xbee series 2. Most people claim that it has a sleep current in the micro amp range. Should definitely help save power.

    I also need to research efficiency on devices like this: https://www.sparkfun.com/products/8248
    I am wondering if using a converter device such as that will have a significant impact on the life of the battery.
  5. berkeman

    Staff: Mentor

    Yes, using a switching DC-DC power supply will let you get most of the energy out of the battery, and will generally be more efficient than using a linear regulator. I'd recommend doing a boost regulator off of a 2-cell battery pack to make your 5V. You can use the 2-cell voltage directly (3.2V-1.6V over the life of an alkaline battery) to power the micropower oscillator+counter circuit, and only power up the 5V when the counter expires. (that's for if you are sleeping by powering everything else off)

    If you want to use sleep mode for the whole circuit instead, it's best to not run the DC-DC while stuff is asleep -- it just wastes power. In that case, you can stack more batteries and use a low dropout linear regulator, since you only draw your main power infrequently.
  6. dlgoff

    dlgoff 3,146
    Science Advisor
    Gold Member
    2014 Award

    I've used "Change-of-State" mode for radio telemetry remotes.

    Planning Transmission Rates

    Are you using Change Detection Mode in your remote radio?

    Sampling Data from XBee Radio in Change Detection Mode
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