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Electric Field Proximity Sensor

Posted by Squintz , 23 March 2009 · 2083 views

One problem that has been difficult for us DIYers to solve is how do detect someone without motion. In other words how do we tell if someone is sleeping in a bed, siting on a toilet, laying on the couch, or taking a shower. During the first Baltimore Hackerspace meeting one of our members demonstrated an EF Proximity Sensor which he had hacked together using an old CB Radio, some custom electronics and the popular Arduino. When you placed your hand in the antennas field the speaker would ramp up. The closer you were the louder the sound from the speaker.

Naturally I wanted to build one of these awesome proximity sensors my self. He has been too busy since that meeting to go over the circuit in details with me so I started looking for the answer online. Take a look at the documentation which you can download from this site: http://www.bik.com/

This circuit design is adjustable from inches to 12 feet which makes it perfect for all the applications I listed above. Add the Arduino and you can interface it to any of your Home Automation controllers. Now all I have to do is actually build it. I'll let you know how it works out.

A commerical version of this that is affordable opens all kinds of doors!
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Dan (electron)
Mar 23 2009 06:09 PM
I have heard about this before, looking forward to the results.
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It looks like some of the original IC components in the schematic that was provided have been disconinued. However, the schematic is simple enough to understand that even I should be able to come up with an alternative solution. It appears to work is by generating a signal and transmitting it on one antenna and then compare it to the signal received by another antenna. The range is related to the antenna length and frequency used. Antenna design is also a factor.
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Here is a nice post from 10 years ago. I don't know why Russell stopped selling the kits around 2000. I expected to see them come out as a commercial product, but haven't heard anything. It was almost like he got a cease & desist order. I thought about buying some, but never got around to it, way back then.

Here you can read more about when it was available:
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Very nice WayneW. Thanks for sharing. That will help me a lot.
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Hey check this out Squintz

Dewdrop-sized Motes Serve As Invisible Security Guards
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How does IR compare with RF, for occupancy sensing?
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IR or PIR (Passive Infrared) requires that you be moving in order to be detected. You could use lasers or beams but that only covers a small area. RF creates a variable size field and if you enter that field you become a conductor and the energy passed to the receiving antenna is increased. You can measure this increase in energy and react to it. With a PIR if you are siting on a toilet or laying in bed then you typically are not moving enough to keep the PIR activated all the time. PIRs usually take 2 steps to trigger them. There was a hack to a PIR on this forum that made them much more sensitive.
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