The AAduino

Update: you can now order the AAduino PCB from DirtyPCBs.com and get a Commadorable 64 bonus PCB for free.

I have been using Nathan Chantrell’s Tiny328 for quite some time as my swiss army knife ISM radio node. Now I wanted a more slim ISM node as my setup with a Tiny328 on a breadboard is not very “deployable”. I could of course 3D print a case for the Tiny328 but I have limited access to 3D printers and do not feel I have the time to explore that exciting part of the maker world just yet. This leaves me with finding off the shelf project boxes with a compartment for 2x AA batteries and the “radioduino” (and in an acceptable form factor). That search came up disappointingly, and surprisingly, short. I did have a set of standard eBay AA battery holders and looking at the 3x variant it occured to me. I needed to shrink the radio node, and the AAduino was born.

Honey, I shrunk the radioduino!

The AAduino is an wireless Arduino clone the size of an AA battery with Keystone battery terminals rotated 180° to act as positive and negative terminals. It is powered by an ATMega328p and is fitted with an RFM69C companion. There is room for two DS18B20 temperature sensors and an indicator LED.

I still think it looks a bit weird :)
I still think it looks a bit weird 🙂

It runs at 8Mhz to allow for greater life span since the CPU can run at a lower voltage. I have fused the 328 to brown out at 1.7V which is a bit out of spec at 8Mhz and slightly below what the RFM69C needs. Running at 4Mhz would be more suitable but I will see how well the node performs when the batteries are draining out.

AAduino, RFM69C side
AAduino, RFM69C side

Since the RFM69C is somewhat wider than an AA battery I used a file to make it slightly narrower. There is some room for that kind of modification without damaging the module. Update, the RFM69C will fit without modification. Next I clipped the legs of the DS18B20 until about 5mm remained and soldered it to the 3x pin header on the AAduino. I then drilled a hole in the battery box where the sensor can protrude and a small hole for the LED to shine through. The wire out of the battery box was cut, shorted and stuffed away inside the box.

AAduino inside 3xAA box
AAduino inside 3xAA box

I use battery terminals from Keystone available from RS Components, positive and negative. There seems to be a cheap eBay alternative but I have not tested those. The + and – markings on the PCB indicates (this is important, read carefully) the positive and negative poles of the battery we are pretending the AAduino is. The Keystone spring contact should be soldered to the + marking and the button contact to the – marking. There is no protection diode here so be careful. Also note! If you want to power the AAduino from a bench power supply, connect the power supply’s black negative lead to the + marking and the red positive lead to the – marking.

aaduino-v2

The 3xAA boxes are also from eBay and there seem to be two different types. One that is really good and one that is really crappy. I will let you in on the secret of buying the correct one. The good ones have a nice build quality and plastics and look like this. Note the rectangular piece of plastic below the battery compartment extending from side to side.

Good 3xAA holder
Good 3xAA holder

Looking at the crappy ones, well you can tell can’t you? In the top left corner it seems someone used a soldering iron on the poor thing. The lid does not snap in place very well and the plastics is really cheap.

Crappy 3xAA holder
Crappy 3xAA holder

Code, schematics and BOM on Github, as always.

136 thoughts on “The AAduino

          1. Mikael BERTHO

            Nice 😉

            It will be very easy with that kind of stuff to get temperature sensor in every room in the house

          2. Johan

            Yup. The extra DS18B20 interface is for monitoring eg a freezer using a wired ‘B20 (in addition to monitoring the room the freezer is located in)

          1. Johan

            In that case you would need a voltage regulator. The AAduino is designed to run from unregulated batteries and the RFM69 does not support 3.7V IIRC. OTOH you could get ~3yrs uptime with good AA batteries according to Nathan Chantrell.

          2. Tom

            I guess, that won’t be a problem… The RFM69 will work fine up to 3.6V… So I just need to use a diode, to have a bit lower voltage. Why I eanna use LiIon cell? The case will be 30% smaller and I can recharge…

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          1. tedder

            Also, I’d love to help organize the Kickstarter with you. I can handle “north american distribution” or whatever else you’d like.

          2. Johan

            I will see what I can do to make the AAduino available for purchase.

          1. John

            Set CLKDIV8 fuse and you’ll be on a safe side with both 8 MHz (1 MHz CLK) and 16 MHz (2 MHz CLK).

      1. Christian Sabourin

        Brilliant! I’d buy 10! If you launch a Kickstarter, you already have my pledge! This has everything and more that I need for most of my projects. It’s no wonder I see you article everywhere!

  8. Roy

    Johan, great talent!

    Congratulations!

    I have a couple of ideas that may require “some” validation. Is there any way to be in touch with you directly? Direct email or Twitter account will be great.

    Thanks

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  10. Mark T

    This is a great idea, and reducing it all down to the size of an AA makes it so much more practical for size-limited tasks. Have you considered the 18650 form factor lithium battery? If the board were that size then you would be able to use it in a 2-cell box with a higher available voltage.

    1. Adam Runner

      Oh goodness, the 18650 idea would be fabulous, especially because a single 18650 would be able to put out an excellent amount of power for a single cell.

      Think if the board was designed to hold a single 18650 (as well as expose a Li-Ion charger / regulator). That would be quite useful for deploying remote sensors.

      1. Dag B

        I am also looking forward to a kickstarter/indiegogo thing.

        I am sure a version to go along with a single 18650 will have uses. But given the self-discharge rates of Li-ion (8%/month @21degC) vs Akaline (2-3%/year), a pair of good AAs will quite possibly result in longer uninterrupted runtime for a low-power remote sensor.

        Also, a charger circuit will add to the cost. Not a function *most* users will utilize very often, I presume.
        But padding the AA-sized AAduino so it sits snug in a dual 18650 box should be doable? And the padding could for example be made up of, say, a tiny microUSB-fed 18650 charger? I am just brainstorming here…

        A joule thief sounds intriguing. But from my understanding of it, it has an oscillator, and hence it also *consumes* power. Not sure if the effect of a JT or any other voltage booster will result in actual longer runtime for the typical usecase. Can it be designed to only be in effect when the battery voltage sags below some threshold? I am not an electronics guy, so I have no clue. But there is no free lunch. Somebody do the math, please.

        I am curious about how much a prebuilt AAduino may cost….

        1. Adam Runner

          Good point regarding Li-Ion discharge rates… I think I might just want an excuse to use all of the 18650s I’ve harvested from old laptop batteries, so maybe I’m biased.

          Lots of excellent ideas rolling around here in this thread. Hopefully we will see some of them come to fruition.

          1. Johan

            The AAduino could very well run on a CR123. It would not last as long as on 2xAAs but would make an even tinier node.

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  18. Toni

    Brilliant!

    This is what I’ve been looking for for so long …

    But, as I’m color-blind, rather a SW techie and have few experience with soldering: when and where can I buy it?

    Also, how can I receive and work with the data on Raspberry Pi?

    1. Johan

      You would need some kind of gateway to receive the data on the 868MHz radio and feed it to the Pi that in turn posts the data to some kind of web service. There are some available radio gateways available. The Emoncms project have one called RFM12Pi that aka believe you can buy online. I build a similar one called BranlyPi for the purpose of learning PCB CAD and SMT mounting. As for the AAduino, I will look into the possibility of making it available for purchasing.

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  20. Josh DeWinter

    Very cool, AND with an ISM transceiver? Even cooler. I have begun tweeting! I’m a Product Manager and technology marketer. A colleague at the large company we work at introduced me to your site. Keep up the awesome creative work!

    twiiter: joshdewinter

    -Josh

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  29. febber

    Combined with an 0.91″ OLED (128x32px, panel size 30×11.5 mm) would be the cherry on the top.
    http://www.buydisplay.com/default/0-91-inch-128×32-oled-display-with-connector-fpc-ssd1306-white-on-black
    http://www.buydisplay.com/download/manual/ER-OLED0.91-1_Series_Datasheet.pdf
    Power consumption should be quite low: max 12/18mA with 50/100% pixels lit , sleep mode 2uA.

    The 15pin FPC connector has the same with (13.15mm) as your PCB.
    http://www.buydisplay.com/download/connector/ER-CON15HT-1.pdf

  30. Dag B

    Johan, have you made any progress w.r.t. finding out if this can produced in any volume? Or would you rather someone else took the idea and ran with it? Asking with an open mind here…

  31. Adam Runner

    What gateway do you use to have all of your sensors communicate back to a local base station?

    I’ve been deploying some ESP8266 based wireless temperature sensors, but these are significantly more efficient….

    Have you tested with Rechargeable AA batteries? (NiMh?)

    1. Johan

      I currently use my BranlyPi to receive data and a Python script to post it to Emoncms. I have not tried rechargeable batteries, I don’t know how they would match up to their non rechargeable counterparts.

      1. Ray Burnette

        @Johan,

        I have had the ESP8266+0.96OLED display running for as long as 4 hours and still going strong; but I have never attempted to record the full life-span of the LiFePO4 cell … my specific need for this device is that it was built as a open WiFi “war walker” … walking around my neighborhood … most of my walks are under 60 minutes.

        If you have not looked into LiFePO4 cells, they are simply great for hobby work. The chemistry never permits any elementary lithium production, so fire risks are low to non-existent.

        Ray

  32. James Anderson

    Hi,

    I was really impressed by this design, what with it being so small. However my concern is that ds18b20 sensors do not work below 3v. What is your plan for when your batteries start to go flat ? something tells me the battery life here that this can actually operate at is not very long because while the microcontroller will run well down to 1.8v, the sensors will not function properly below 3v, which kind of defeats the point.

    What do you reckon?

    Regards,

    James

    1. Johan

      Hi James,

      That is indeed a very good point I need to consider. Others seem to have had success with the ’20 below 3V. I’ll look into that one.

      Regards,
      Johan

  33. Kaz

    This is an excellent idea! I’ve been working on a small FM radio for years to hear 72-76MHz transmissions, and one thing that’s kept me from making a bunch of them is the form factor. With this, I can stick the radio in the box and just drill a hole for the headphone jack and I’m in business! My design can fit on a 14.5x50mm board, so that should be just fine. Thanks for sharing!

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  36. Dag B

    Johan, I see you have updated the article to point at DirtyPCBs boards for the AAduino. (Not sure when that happened.) Thank you for that.

    I am still hoping for a prebuilt device. Pretty sure I am not alone in that regard. From the Commadorable 64 comments, it appears you are still working out the details for prebuilt AAduinos. Is that correct?

    Dag

  37. Franco

    Hi Johan,

    I found this amazing project and I want to buy.
    One question: if I buy from DirtyPCBs AAduino I’ll receive AAduino mounted and ready for use?

    Thanks a lot and very compliments to you

    1. Johan

      Hi Franco. Thanks! If you buy from DirtyPBCs you only get the PCBs but there is a plan as we speak to start a crowdfunding campaign for building lots and lots of AAduinos. Stay tuned 🙂

      1. Louis Croisez

        868 MHz. OK.
        And about the antenna, could you give me its characteristics, like total length of the wire, diameter of the spires, and tickness of the wire?

        1. Johan

          I am afraid I cannot. When not using a piece of wire cut to the right length I use scrap antennas from discarded 868MHz devices and have still to find a source of these.

  38. Caspar

    Hello,

    stumbled on this perfect mini node – do you know wether it will work with a RM95W instead of the RFM69C? Looking forward to be LoRa compatible…

    Cheers

    Caspar

    1. Johan

      Hi Caspar,

      Looking at the pinout of the ’95W I see it’s not compatible with the ’69CW footprint. I have not dived into LoRa yet but will do a LoRa version when the day comes.

      Cheers,
      Johan

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