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Some help with my project

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Posted · Original PosterOP

Hey everyone, rather odd question but I feel like if I'm going to get an answer anywhere, it's here. What I want to do is wire something up to where it will only turn on when close to an object, some sort of sensor. If it isn't near the specific transmitter, it wont go off. If the the receiver is, lets say 2 inches away from the transmitter, then it will turn the device on. Maybe having a switch to turn the transmitter on and off. ANOTHER issue I'm having is that the device I want to only turn on when close to a transmitter has to be very, VERY narrow. I'd say around an inch wide and in tall. If anyone can help me out on this, that would be fantastic.

I included a VERY basic diagram of what I'm trying to do, don't even know what I drew up in five minutes would work or not. If not, tell me. If it does, tell me. Any suggestions, tell me. Links to get the stuff, fantastic! Tell me. Any help is appreciated.


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complete overkill but fun project: use the old Intel dev kit. µC + energy efficient ANN. The ANN can be used to decode/guess the activation signal.


1. normal µC with NFC in a higher sleep state on the recvier side

2. passive receiver side -> magnet switch and on the transmitter side on off those magnets you can turn on and off by applying power once.

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NFC tag will do what you want and be extremely small.

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Posted · Original PosterOP

@James Evens I couldn't find any magnetic switches small enough, if you can, can you provide a link to one?

@Enderman Could you also provide a link to one. I'm assuming I'd need to get an NFC reader and tag, I can't use a phone to read the tag.

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6 hours ago, PotatoRynn said:

@James Evens I need to be able to fit a light, a battery, and the switch inside of a 1 inch wide, 1 inch tall, 5-6 inch long tube. Sorry for the long response time, by the way.

I was looking at your project, thought I might give you some ideas.

If you wanted to go the magnet route as @James Evens suggested, this reed switch might fit the bill. Its small and compact, not sure what the effective range is though.

Another option would be line of sight, your transmitter could consist of an inferred LED, or multiple, and your receiver could be based around a phototransistor.

The receiver could look something like this (super simple to do btw)


This would give you a very narrow window for your rx/tx, and the range could be adjusted by the output intensity of your transmitter LED.

As far as power goes, I would use a CR-2 or CR-123A type battery, they have high capacity in a small package, they are rated at 3v, not 1.5v like a AAA's, so you would only need one.


Note: If you do decide to use the IR phototransistor, make sure the wavelengths match when your sourcing parts. I believe the one linked above is most sensitive to 940nm.


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I suppose, if you wanted something a little more complicated, you could use a dev board with on board packet radio, like this one.

The dimensions overall indicate that it would fit within your proposed housing constraints. The same company offers very small lipo batteries that you could power the board with. If you had a pair of them, I imagine you could cook something up that would fit your needs.

In regards to the 'distance' dilemma, If the transmitter intermittently broadcasted a 'code', the receiver could then echo the code with an added suffix. This would allow the transmitter to relay the code with the suffix back to the receiver. why do that? well it would allow you to calculate packet delay, giving you an indication of distance.


(poorly constructed flow chart of science)

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