Slim CR123A (2AA) battery node..

  • Hero Member

    Have been playing with the "Slim 2AA battery node" and a small motion sensor. As most motion sensors are not comfortable with voltages under 3v, a CR123 rechargable 3.7V cell is used. This makes the design even smaller ;-).
    The "spider" breadboard:

    The IR detector has an on-board regulator which is used to power the ATMEGA and radio.

    Just need to wait a little longer for the housing.. I will post a picture when completed.

    The rechargeable battery mentions 2300mAh which is not realistic, but from experience it will keep the node alive for at least a year before a recharge is needed (outdoor use). Power consumption of the node is mainly from the motion sensor (~45uA) total 55 uA.

  • @AWI what is the range and sensitive of this PIR?

  • Hero Member

    @Francois This is the spec:
    Which is in line with what I experience.. around 3 meters. As can be seen in the picture I bridged the diode (removed wrong polarity detection) and used the output from the regulator (LDO, 100mV drop). This way it can be used with a rechargable LiOn cell (typ 3.5V - 4.1V). upload-2f5f66e7-3278-48ea-b47c-b30742acd49d


  • Hardware Contributor

    @AWI Great!! I have a very similar project pretty high on my list. My thought was to use the 3.3V mini step-up though. Perhaps 3.3V only to the PIR and then have it all to sleep timed cycles by controller command.

    How's the li-ion battery usage considering min LDO voltage level. ? I remember some discussion here.

    I read that the motion detector has "Static current: <55uA". Have you measured it and can confirm this? Do you think those 55uA is related to LDO-reg quiescent current (which could be bypassed) or is it to keep the PIR "warm".

  • Hero Member

    @m26872 I had the same considerations but decided to go for CR123 cells. In most cases I use the non rechargable cell which is perfect for low power because it has a stable ~3 volt output, can power the radio and arduino with no extra components, has minimal self discharge, etc.

    As the PIR sensor needs > 3V I used the rechargable one (typ 3.5V - 4.1V). With the on-board regulator (LDO) of the PIR this works fine in almost all cases. LDO quiescent current is < 5uA. I measured 46uA (no movement) and 62uA (movement) so quess the PIR and controller are responsible in that respect.


  • According to this reply, some people faced radio problems when using the CR batteries.
    Did you face anything till now or the node is working fine ?

  • Hero Member

    @ahmedadelhosni I have not had any "problems" from using CR123 cells in any of my designs. The "hear say" is probably from the fact that CR123 claims for battery capacity are highly overstated. My own experience indicates between 500mAh and 1.200mAh including the very cheap batteries.

    Another thing to keep in mind is that there is a large variation in battery voltage, so you need to know what you are doing,

    For me the advantages are:

    • Very low self discharge (> 10yrs)
    • No leakage yet. My first (expensive) battery sensors were ruined by leaking batteries...
    • size
    • High voltage/ large capacity relative to size.
    • price €1-€3 for a cell (you only need one which lasts for long)
    • availability (I stock them)
    • a lot of rubbish on the market/

    I would welcome any fact based comments/ issues

  • Hardware Contributor

    @ahmedadelhosni @AWI
    Sorry for being vague there, but that discussion was only about Li (C) round (R) "coin cell" batteries. CR1220 was linked. It does not apply to the CR123, AFAIK. I added "coin cell" to that post in the other thread.

  • @m26872 Somehow I understood now what you mean but I want to make it more clear. You meant that the problem was with "coin cells" only like CR1220, but the CR123 (with doesn't look like a coin cell I guess) no one complained about it. correct ?

    The other thing. If this was what you mean, so even if it was a "coin cell" with 750 mah (for example) it may have a problem ? or was the problem related to that CR1220 has 35 mAh and that was too low ?


  • Hardware Contributor

    Yes, I have no broad knowledge about coincells, I just haven't seen any proven designs with them and hence not used or tested them myself which was what I relpied to you in earlier discussion. I think Hallard's ULPnode intro was one of the references I had in mind.

  • @m26872 The link is helpful and I understand now. Thanks

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