8/06/2013

Power supply for remote sensors

Presentation: How to supply power to microcontrollers/ (remote) sensors with low dropout (LDO) voltage regulators and batteries


"Classic" 7805 Voltage regulator
On August 5 I had a short presentation at the Makerspace Attraktor in Hamburg on how to supply independent power to devices like standalone microcontrollers or (remote) sensors.

 The talk gave some comparison about different low dropout voltage regulators which are by design very well suited for battery powered devices. Decision finding on what parts are most suited and design considerations for independent sensors were explained detailing a remote temperature sensor project I'm working on for about two years now.

XBee temperature sensor


You can find the presentation (in english) here

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7 comments:

  1. Hi Markus, thanks for you presentation: that's what I was looking for.
    Just a question: why a voltage regulator if you are using battery? I mean, since it is not a classic 78xx that maintains a fixed voltage (e.g 3.3V) and it follows Vin "stabilizing" it, using batteries it should not be needed. Where I'm wrong?

    Thanks,
    Massimo

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  2. Hi Massimo,
    at the moment I'm using 3 AA cells for some sensors which means the voltage could be 4.5 volts or higher. That's way too much for the XBee so I have to lower the voltage to a maximum of 3.6 volts (XBee works from about 2.7 to 3.6 volts). To utilize the batteries which are normally discharged to about 1.1 volts before getting bad, I chose the 3.3 volt LDO.

    Best regards,
    Markus

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  3. Hello Markus,

    I'm building an outdoor sensor network to monitor soil moisture, temperature, and humidity, and would like to use a standalone xbee at the remote site. Your power consumption numbers are very reassuring.

    I will be building a soil moisture probe using two galvanized nails. My concerns are that 1) the necessary voltage divider circuit will be consuming power even during the xbee's sleep cycle, and 2) as I understand it, constant voltage across the nails will cause corrosion over time.

    I believe the best way to resolve both issues is to have the probe "powered off" during the xbee's sleep cycles, saving power and mitigating corrosion.

    I can't tell based on your posts if you are powering your temperature sensor all of the time, or if you are using a digital output pin or some other magic to power up the sensor periodically.

    I'd appreciate any thoughts you may have on the topic. Thank you.

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  4. Hi Matt,

    the temperature sensor is only powered when the XBee is awake. It's tied to an analog Input and it's sampled only then and send to the host.
    The only thing which consumes current is while the XBee is sleeping is the voltage regulator that only needs about 1µA quiescent current.

    Markus

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    Replies
    1. Thank you for the reply. I never saw a diagram posted of your remote sender. I suspect it's a pretty easy circuit, but I'd still be interested in seeing something if you have it.

      In particular, I'm curious if you using the same temp sensor that you used for the base station, or something like the TMP36. I'm also interested in how the sensor is powered.

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  5. Hi Matt,

    I just posted the wiring of the temperature sensor

    http://lookmanowire.blogspot.de/2014/04/xbee-remote-temperature-sensor.html

    Hope that helps

    Markus

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    Replies
    1. It does - immensely. Thank you. I was curious about pin13, as the documentation mentions it briefly but provides little other detail.

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