Revisiting Light switch controlled plug wireless link

My first attempt at wirelessly controlling outlets could be considered a failure, even if technically it works. My solution was simply too unreliable and was rather awkward to assemble. The main failure was my decision to use the cheapest wireless receiver and transmitter pair that I could find. Unfortunately they proved to be completely sporadic in anything but ideal conditions. With a nice pair of antennas they probably work fine, bu with the small enclosures that I was using there simply wasn’t room for a quarter wave antenna (just over six inches). Instead of buying a helical antenna which would fit in the enclosure looped the wire antenna around the inside. It worked, but not well enough. When the lighting in the room depends on a wireless connection, a light randomly turning off and back on makes it very obvious that my solution was not good enough.


The other problem was how difficult it was to put the boxes together. I decided early on that I would simply use old cell phone charges that we had laying around for the AC/DC converter to power the micro controller. What I failed to consider was that these boards take up a lot of space and the extra wires would make it a spaghetti bowl of wires.


I really really want to walk into our living room, flip the light switch and have all of the lamps turn on and off together. I also like being able to use devices how I want to, and I haven’t seen anything commercially available that I like.


At this point, I have decided to put more time into my wireless plug control boxes and make them work. To avoid a lot of the wireless link issues I have decided to use the MRF89XAM9A 915MHz transceiver module from Microchip. It has a properly designed antenna (with impedance matching), has a tx/rx buffer, and is even FCC certified.


For powering the board I have decided to integrate an AC/DC converter onto the circuit board, which will save a lot of space and aggravation. Dealing with main voltages is always dangerous, so be careful. I ultimately decided against using a transformer free design because of the power levels needed for the transceiver (27mA at 3.3V). I would need a huge capacitor rated for use at 120 VAC, and they would have cost more than a transformer and rectifier.


The transceiver module is backordered until March 2012, so I may not get a chance to do much more until then.

3 thoughts on “Revisiting Light switch controlled plug wireless link

  1. Pingback: Motorized Furnace Vent | Square Penguin

  2. Max,

    I have built it, and in it’s prototype form it works great! I’ve been distracted recently with Z-Wave devices and have been busy getting the Aeon labs USB controller working with a Teensy 3 + Ethernet to allow for internet control of the Z-Wave devices.

    I’ve got a thermocouple sensor board that is nearly done that does use the same MRF89XAM9A 802.15.4 wireless module. It’s practically done and I should be posting about it soon!

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