Reed Switch normally open or normally closed



  • Hi everyone,

    I'd like to show you a recently completed project. A reed switch-based sensor that can be implemented either normally open to normally closed. (I like normally open (with sense magnet) for low/no current draw, but normally closed (with sense magnet) can also be realized).

    If one does a bit of research on reed switches, it can be found that the switches can utilize two magnets for making a normally open switch (without sense magnet) a "normally closed" switch (without sense magnet).

    The idea is to drill a 7/16" hole in the jamb of a door and imbed the reed switch, then imbed a magnet into the door to complete the install. One wouldn't even know it is there; I would have a node close by to connect directly to the switch in the wall, (for me, new construction will allow this). Have a look, let me know your thoughts.

    I have designed a PCB and case (3D printed) for the switch. The PCB is straight forward, I'll leave that to anyone who'll want to replicate it, but the case took a few revs. Here is the prototype.

    image4.JPG
    Figure 1. Side view of the switch PCB. The switch is the glass tube; on the other side, I super-glued a magnet to the PCB to change the switch from normally open to "closed" (conducting). In this configuration the switch is closed (conducting), and when another magnet (sense magnet) is brought near (must be opposite polarity) the switch changes to open.

    image3.JPG
    Figure 2. Reed switch PCB and case.

    image2.JPG
    Figure 3. Reed switch fitting into case.

    image1.JPG
    Figure 4. Reed switch inside case. ready to be inserted into drilled hole in door jamb. The wires would travel to a node through a smaller hole at the end of the case. (if that makes sense). The sense magnet will be brought close to the 'top' of the cylinder when the door is closed making the switch 'open'. In this configuration, I believe a burglar would have a very hard time cutting wires that are inside a wall, so, no worries and I value normally low power (no current) operation.

    Here is the SketchUp file used to create the 3D print...you should install the "export to .STL" extension and then print away. The PCB is 1.6 mm thick. ReedSwitch_WorkingSet.skp

    Oh, and for those in the USA, I get the magnets from K&J Magnetics





  • @gadu sure! But these are 1/10 the cost (good for when one needs ~30-40), and I'm not sure the commercial ones can be changed from normally closed to normally open with sense magnet nearby like this example. BTW, this one is 10mm x 32mm, so about the same size as in the first link you suggested.



  • One more thing...the actuator magnet I'm using is 1/4" diameter x 1/16" thick. (6.35mm x 1.56mm). So, I think this actuator magnet is also much smaller.



  • You're perfectly correct! πŸ™‚



  • Just bought these online, thought i'll post this for info.
    Didn't know these 3 legged glass reed switches exists.

    "NO/ NC SPDT Reed Magnetic Switch Replacement 2.5x14mm Ri-90 L2l6"

    link text

    0_1533772926891_NO_NC SPDT Reed Magnetic Switch.PNG



  • @sglue Hello, I have these reed switches which have two output states... NO & NC.

    How would one go about have a two state reed switch on MySensors. I am trying to figure out how to do it on a NRF51822 chip on a coin cell battery.
    Basically I am trying to port this code into MySensors.
    MBED Link

    I need a starting point to take it forward. Any kind of help will be great. Thanks



  • @Puneit-Thukral

    Sorry can't be of much help.

    I used them for my garage door as limit switches, they tend to break easily and on hot days get false trigger.
    Now using micro switches same thing happens.
    Will try yo insulate the switches next.



  • @Puneit-Thukral said in Reed Switch normally open or normally closed:

    How would one go about have a two state reed switch on MySensors.

    Can you clarify what you want exactly? Usually these are used to decide if something is near or far from the switch by means of a magnet. Therefore if no magnet is present the NO will be open and NC will be closed. As soon as a magnet is moved close enought to trigger the reed switch those values swap over and NO will be closed and NC will be open.

    The reason some switches have both states is that different systems will use NO or NC loops for detection and a relay that has both can be used in either.



  • @skywatch I recollect reading in another project that a NC /NO type reed switch consumes less power than a single output. In that project the author was setting the pin to "floating" when it opened to reduce the power consumption.

    Is such the case? I
    Thanks



  • @Puneit-Thukral I guess it depends on the hardware the user was using and how it was wired up!

    Really it is just an on /off switch. Well, in your case 2 on/off switches with the connectors commoned at one end of the switch.

    Is this for a door/window/similar type application?



  • @skywatch in my case I will be using for a door sensor.



  • @Puneit-Thukral Saving power by floating the pin may return spurious triggers, pull-up resistors give a solid open/close.
    The gas meter here has a simple reed, now in it's second year on 2xAA at ca 30,000 actions/year, simple high value resistor bridge with a cap across the lower to ground to minimise noise and deal with "bounce" yet minimise current used.



  • @zboblamont Thanks.. this is promising.. Of course, I was trying to complicate this way too much than needed. I will work with the regular reed switch.





  • @skywatch Yes I did try this first.. but I am trying to merge reed sensor with BME280 running on battery (preference is of a coin cell) and I am not using Arduino pro mini or similar. I am trying NRF51822. I did search the forums and openhardware. Most of the sketches available for this board are for NRF52 series board. I already have 10 of the NRF51822 boards and I would like to use them.
    On another thread I posted my sketch where I merged but it is not working for me. 😞

    Alas, my struggles continue. I am not a programmer but a copy/paste kind of a person. I am sightly modify code but still cannot write from scratch..getting there slowly.

    Cheers!



  • @Puneit-Thukral OK - post the TWO codes completely here and I will TRY and help you merge them. That said I have NO experience of the 51822 and so you may still need help. I am fairly busy at the moment but in a few days I should have time to help you out.



  • @skywatch thanks a lot for offering to help. I think I have made some headway.
    I used @NeverDie sketches. The one for nrf24 or RFM69 don’t really work well with waking up the nrf51 chip or maybe I made some mistake and were consuming way too much power.

    Anyhow , the test sketch is running and interrupts are working fine as well as the bme280 reports fine.
    Tomorrow I will move it a battery powered and observe.

    Cheers!


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