Low power PIR breakout board for Mysensors and evaluation

  • Hardware Contributor


    I like to make my boards small as I can (with my "little" knowledge, lol) and, like lots of you I needed a small, slim and of course low power PIR sensor. I don't like chinese HC-SR504 board because there are big capacitor on it. Not easy to integrate in small enclosure. So I decided to re-design this chinese board with smd capa.
    But, Anticimex pointed to me a very interesting app note : ST AN4368. Thanks to you @Anticimex for your valuable advise :wink:

    Note : I ordered pcb few weeks ago, it should not take lot of time now to get them. I ordered it at oshpark, as board is small, price is cheap.

    So this board is based on this ST appnote, and especially on the first schematic in it (based on TSU104 opamp, more low power).As app note state, it should be somewhere 23uA. I am using a nanopower nand gate. I didn't find better for this ref..so the board should be 1uA more. I hope it will stay between 23-25uA which is not bad I think..

    I have made few changes for easy testings:

    • 2x potentiometer added
    • debug points
    • optional led on Out Signal (for debug)

    Size : 24x19.7 (mm)
    Components size 0805.

    Now some screenshots:


    Boards can be ordered here : https://oshpark.com/shared_projects/Dc6Tlrt1

    Eagle files and BOM on my git, here : https://github.com/scalz/MySensors-HW/tree/development/LowPowerPIR_Breakout

    So it should work, as I followed app note. Changes I made are minor. And I have taken care of routing to try to not have problem on analog trace...


  • Contest Winner

    Nice! You beat me to it :D
    I might do a MYSX module out of it if it turns out to work as good as the app note suggests.

  • Admin


    Which PIR sensor element are you using?

  • Hardware Contributor

  • Hardware Contributor


    I have received pcb. so for the moment it doesn't work like I want. I have not digged a lot. I have just soldered it and powered with two aaa, 3.2v. Led was triggering too much so I checked potentiometers. and it triggers ok but the range is not great for the moment. maybe 2.5m.
    So I looked briefly voltage levels with oscillo and I think I need to check and tune resistors to see if it is about comparator window (resistors), pir sensor or the lens.

    So no good news, no bad news too. it works well at 1m :laughing:
    but I have not said my last word :smiley: I hope to have some time asap. it would be cool if it worked.

    another thing too: I will update files. not a big mistake but good to know. the silkscreen for the pir sensor is not well oriented.

    Here some pics

  • Contest Winner

    @scalz cool! Nice work. Did you manage to grab some current measurement to see if it operates within reasonable ranges for battery operation?

  • Hardware Contributor

    @Anticimex : hi :smiley:
    I didn't checked at first, because I mounted the led. But I just removed it, and here first results with uCurrent:

    • 24uA with no trigger
    • when it triggers it oscillates between 24-27uA. so it seems to work as announced in app note.

    it just needs to check the opamp res divider (3rd stage comparator) I think. Because when I did some tests, looking with my oscillo, voltage levels was moving well when at 3-4m. but it didn't trigger. so I suspect that it needs to refine the comparator window (sensitivity...)

  • Contest Winner

    @scalz that's excellent. I believe you really have something here. Battery operated motion sensing would be awesome!

  • Hardware Contributor

    @Anticimex: yep it would be great. Did you order pcb? if you want I can send one to you with pir sensor and its lens (free :wink: I don't know letter postage fee from France to you but it should not be expensive I think.).same offer for you @tbowmo or @Hek :wink:
    In other hand, I have not enough opamp...and pots so if you have these in stocks..

  • Contest Winner

    @scalz Thats very kind of you, but I am afraid I have not got the time to investigate more closely currently. Little baby present and Christmas coming up :)

  • This post is deleted!

  • Hardware Contributor


    just a little update, I made few tests (between two projects :persevere: ), trying to see if it could be more low power. And yes it can, it needs for instance to use higher res of course! 10-15M and increasing a little bit capacitors (100nf instead of 10nf) helped to stabilize and I was near 5uA!
    Unfortunately, I didn't had big success with my false triggering...and range increased a little bit, a little bit better too with another sensor (LHI968).

    But that is not my biggest concern here. And I am curious to know what you think. Like you I am searching a low power PIR <10uA, reliable, and not expensive.
    But for low power, we can encounter some case like:

    • holidays : lot of triggering breaking sleep mode and low power.
    • In deepest sleepmode, we have no time reference for blind time etc...
    • So it would require some tricks to handle everything in sketch and finally maybe the overall power consumption would increase a little bit (few uA).

    In other hand, @Myna made a board with E931.96. I don't know if he got it working but I think this ic could solves all this problems.
    MCU deep sleep mode could be possible, and E931.96 could handle false triggering, blind time before retriggering, low power (I think it could equals to my small board), and finally, not the least, it seems that it autocalibrates regarding the sensor. Very interesting in fact! Too bad, it seems it is available only at professionnal supplier.

    So I am asking to professional supplier (Avnet) what could be the availability for this chip. I am already in contact with him for an other interesting chip. It could be great if we could have hand on this ic.
    In the mean time, I have ordered some from aliexpress (I hope it's not clone!).

    That's all. Thanks for reading, and for feedbacks!

  • Hardware Contributor

    Small is small! and more simple :) I will order it at oshpark.

    Component size : 0805
    I hope that will work :) I have ordered the ic at aliexpress. Let's see if it is genuine...if yes, it is not expensive compared to opamp..on the previous board. I am dreaming lol!

    @Hek: I tried to upload another simple eval board at openhardware but I was not able to save/upload it.
    " Unable to save project. Please try again later or contact support."
    So, I will retry later ;)

  • Hardware Contributor

    just a very small update to tell I'm pretty happy: I have just received my PIR chips order today (e931). Another thing to do now : a lib and look if it's fake but I hope not! stay tuned ;)

  • Scalz, which news about e931 ?

  • Hardware Contributor

    I will post some news soon ;) multiple things in progress (hw & sw) but now I'm better organized to speed up my dev in my hobby time lol

  • You shut down work on TSU104 version?

  • Following this thread with interest! Keep up the great work! :+1:

  • Hardware Contributor

    yep for the moment, I have a lot of e931 to use. but I had some ideas for the tsu104 so I will look at it later but don't know when yet (at the end of my todo..)

  • @scalz said:

    I will post some news soon ;) multiple things in progress (hw & sw) but now I'm better organized to speed up my dev in my hobby time lol

    I was just thinking the other day, is there any sort of post already going around here like "show off your workbench / work area?"

    I am getting ready to purchase my initial supplies and some small cabinets, soldering station, etc. which will be, initially, pretty meager but I thought it would be fun to show off my little area, and I'm sure some people here have much more impressive work spaces that I'm sure many would be interested in seeing. :)

    If not, I think I will create one eventually, when I get my area set up. :)

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