An Awesome Wireless Motion Sensor

Wireless sensor networks are nothing new to Hackaday, but [Felix]’s wireless PIR sensor node is something else entirely. Rarely do we see something so well put together that’s also so well designed for mass production.

For his sensor, [Felix] is using a Moteino, a very tiny Arduino compatible board with solder pads for an RFM12B and RFM69 radio transceivers. These very inexpensive radios – about $4 each – are able to transmit about half a kilometer at 38.4 kbps, an impressive amount of bandwidth and an exceptional range for a very inexpensive system.

The important bit on this wireless sensor, the PIR sensor, connects with three pins – power, ground, and out. When the PIR sensor sees something it transmits a code the base station where the ‘motion’ alert message is displayed.

The entire device is powered by a 9V battery and stuffed inside a beautiful acrylic case. With everything, each sensor node should cost about $15; very cheap for something that if built by a proper security system company would cost much, much more.

39 thoughts on “An Awesome Wireless Motion Sensor

  1. 9V batteries are kinda famed for their terrible energy density, especially ‘cuz they’re almost always coupled with linear regulators. But he does say he’s going to try using LiPoly batteries later on.

    I’d be interested to see what kind of runtime he eventually gets.

    1. We have wireless PIR sensors as part of the security system at our home.

      They transmit about 50 meters or more, which is perfect for a regular sized yard. I think the units use a CR123 battery pack (2 in parallel?). I’m not sure of the transmitter tech used, but it is capable of ‘communicating’ rather than just send a ‘I detect something’ signal: You can monitor the sensor’s battery condition remotely by sending a query to the alarm base station via SMS etc.

      Here is the clincher: It’s been more than two years and none of the sensor’s batteries have been replaced!

      Check out for more info on the system.

      1. CR123s are primary lithium cells. They have something like 3× the mAH of an ordinary non-lithium AAAA or 9V battery. Two of them in parallel will exceed the mAH of a 9V battery by a factor of 5 or more.

        My big concern with the system he’s built is that (9V+linear regulator down to 3.3V) means he’s throwing away close to 2/3 of the battery life as static dissipation in the regulator. Just starting off with a lower stack voltage addresses that; even something as simple as starting with three AAAAs in series instead of six (which is a 9V battery) would be enough to shut me up.

        9V batteries also have other problems, like “comparatively high series resistance” and so “bad for any use case that even instantaneously momentarily sinks hundreds of milliamps”. But I don’t think that’s a problem in this case.

    2. Not only that, the non-recharable 9V batteries are also bad for
      capacity vs price at a retail store. For about the same price, you can
      easily get a few times more battery by weight for the other packages.

      One of the things to watch out for is that the current consumption of
      the regulator has to be considered for a low power device. The average
      “7805” regulator uses an additional 5.2mA (typ) 8.0mA (max). A decent
      regulator for battery operations would only use tens of microamps.

    1. Clearly you have never worked on modern Apple equipment (or ones matching their qualities). It is becoming more popular to use adhesives in electronics because it costs less to manufacture, weighs less, and even takes up less space than other types of fastening materials.

    2. Guessing you didn’t click the link? It’s not glued to the battery the boards are glued together and I’m guessing they mean the low cost and the nice polished case when they say it’s designed for production.

          1. Mass production is definitely not 1-10 units. For a small hobby setup at home 100 might be considered mass p. Go to the smallish pros like Seeed then 500 or rather 1000 is mass production. Go to the real pros then they will laugh at you if less than 10K for a simple product like this.

  2. The 15$ seems on the low side. Especially as the clone he’s using is 18.95$….

    I think using an Attiny and a 1$ 433mhz transmitter with a PIR is the best option. However you would need to add a 5v mosfet as the transmitter could use 12v for better transmission.

  3. Some alternatives to the Moteino.

    arduino + nrf24l01+ = 12 USD
    nrf24le1 = 7 USD

    But that only gives me <100m range with good basestation, and the cheap remotes. Do you really get 500m with RFM12B?

    1. You could go with the nRF9E5 instead of the nrf24le1. It would have a range close to the RFM128 and is also an SOC but it is based on the 8051. I really would like to see some small experimenter boards based on the NordicSemi SOCs.

  4. Just a few, random thoughts…
    1. The PIR sensors have an IC that works between 3 and 5V. They also have a low quiescent current LDO that provides 3.3V to the chip.
    2. That can also be used for the radio and micro since it is 100mA one.
    3. 3xAA (~2Ah) will be 8 times better than 1 9V battery (~0.25Ah), but only about 50% bigger. it may work on just 2xAA for a while…
    4. Battery life will depend a lot on how much movement there is and how often you transmit that there is movement.
    5. Although the sensors claim to draw 60uA, in the batch of 10 that i have, some went up to 200uA in idle (no motion, after some minutes of stabilizing time).
    6. These tiny sensors are not as sensitive and reliable as the cheapest version of security wired sensors. They seem to be much easier to trick by just moving slow. That is why a real security sensors cost much more. There is also no guarantee that these little devices will operate for such a long time.
    7. Out of the 10 sensors like this that I have bought none were defective but 2 were very very insensitive.
    8. It is possible to build this while thing cheaper if you just use a DIP atmega8 instead of a board with a smd chip on it. 8K of memory is enough to just transmit something when there is motion.
    9. About 6 months after building this I had to replace one of the sensors, it simply stopped working.

      1. Mats, I didn’t suggest using arduino, i suggested using a microcontroller directly. Also taking it personally, i don’t use arduino or anything related to it.
        I also said that 8K is enough, not that 8K is required. I gave the atmega8 as an example here because it has enough space to fit reasonable radio packet handling and it will be reasonably future proof. Going down in scale, a 8pin 1k micro will still cost you 60% of the cost of an atmega8.

        1. I forgot the ;-) in my previous comment. Suggesting a mega8 made you sound like a clueless arduino fanboy. (and here I’ll put a ;-) to be safe).

          But the Mega8 is horrendously expensive and as far as I remember not a low power device like the one of the Picopower devices from Atmel or the XLP from Microchip so it’s really not suited for a low power application.

          Comparing ~$4 (at Element14/Singapore) for a Mega8 to between $0.5 – 0.8 for a low power, low pincount, low memory mcu like the pic10/12 series I’d say that there are significant savings to be done.

          But don’t get me wrong here, there’s nothing really wrong with the arduinos, I have a handful of them myself. And I sometimes actually use one for making a quick test of some device. But in my about 20 designs I do every year I always select the cheapest and most suitable microcontroller for that particular project. This year I’ve used the whole gamut from XMEGAs and ARM Cortex-M0, down to the itty-bitty 6-pin pic10F series.

          Choosing the right parts to use for building stuff is important. Or else the old saying “If all you got is a hammer, then everything looks like a nail.” is quite applicable.

          1. Mats, you are forgiven ;)
            It really depends where you buy the components from. I also forgot to add the A at the end, atmega8a which is the newer and cheaper version. I buy from where one costs 1 eur in 5+ quantities and drops to 0.8 in 100+. Other distributors might favor other manufacturers, so it might be cheaper to buy something else.
            At hobby level, I buy the micros in quantities of tens. The atmega8a is my favourite micro because i can use it in 90% of the small things i build. It is hard to justify ordering a new micro to save 0.5 eur, unless i need the smaller one for technical reasons(like space or power consumption.

            I don’t think the hammer analogy is good here. It’s more like having a very large tool set when all you need is a simple screwdriver.

    1. Like your site and enjoyed reading the LED article. The ROI point in the decay in intensity is excellent information and I hope it contributes to awareness of this as LED is obviously not mature enough for many applications.

  5. I am wondering is you monitor that battery as well? Seems like it would be a good feature to add so the node could tell you when it’s battery needs to be changed.
    An option to turn off the led so to save power and to control it from the wireless link could also be handy. You could have it blink to when you are looking for which one to change the battery on.
    If you used one of the USB friendly Arduinos you and a TP-Link router you could make a cheap wifi version of this. maybe add a hub and a USB camera as well.

    1. Of course an analog pin can be used to monitor the battery.

      with a router you don’t even need to have a micro-controller, you can re-purpose the LED I/Os to directly read the sensor. with some hacking i think the webcam may be fitted directly into the box.

    1. The sensor detects change in infrared radiation, usually across 2 elements. This change is produced only if the moving body has a reasonable difference in temperature compared to the environment and is moving reasonably fast.

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