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How can we build a cheap detector that senses a cellular (electromagnetic?) for use as a switch for a computer? Answered

Hi all,

we want to use a cellular phone as a "switch" to control a multimedia show.
We thought of a cheap sensor that must be able to detect electromagnetic waves through a store window. We thought of phones because everyone has one in they pocket, phone is simply the source of the field.
Idea is that customers can move their mobile phones in front of our store window to control a multimedia show in a simple way (forward, backward, pause), so in the end three or four different switches glued to the window would perform as a "control pad" for the computer.

Maybe there is a way to base this project on products readily available which can be remodeled.

Thanks for sour suppport and ideas!




7 years ago

As far as I know EVERY electronic device send out electromagnetic waves. Basically, we just want to sense an electronic device (must not be a cell phone), so we have no contact with a "button" or whatever. No Bluetooth, nothing required on the cell. Just the device itself acts a a transmitter. We want it to work with mobile phone because thats what everybod has with them.

The queston is: Can this be done thru glass?

The call-home ping of a cell phone happens every 5 minutes or longer when the phone isn't being used. If the phone is close to a cell station too, the transmit power is a lot lower. The only thing you've got, guaranteed, is the ping.

What you want to do can't be done, except optically !


Okay, then please explaint to me the existence of this instructable:
In the last picture they have a MacBook that triggers a reaction.

My fear is that the glass windows will not let anything trough, tough.

we want to use a cellular phone as a "switch" to control a multimedia show.

...what you have in the cited 'ible is a metal detector. In fact, it WILL detect metals through glass.


Hey, thats good! BUT: Is there enough metal in current mobile phone (like iphone) to get detected?

The only time you should get signals out of a cellphone is when it is transmitting making a call. You might want to set up some array of motion sensors so people can just wave their hands in front or maybe detect the light from the cellphone screen? There are a few instructables for making touchscreens or optical recognition of hand pressure. Or make a giant mouse for them to push around in front of the store. Good luck.

That's not actually true. A phone sends a "I'm here " signal to the network every few minutes when its not actually in use, so the network can route calls to it.


True, phones do ping the network to stay alive. Not all phones are bluetooth capable and those that do have to be configured to be activated.

No, but its a more reliable method, if present, than just trying to hear the net ping.


There are ways of doing this via BlueTooth.