Transmitting small, low frequency analog signal a few feet
Posted by rptort at
I want to wirelessly transmit an electrical signal that's approximately less than 1 volt in amplitude and around a few hundred Hz in frequency. The distance is only a few feet. I don't know much at all about wireless communication. To my knowledge, bluetooth is used for relatively short distances, so that's why I'm in this forum, but I'm open to any standard (whatever gets the job done).
Also, the hardware needs to be small. Any ideas??
If you have any questions, please let me know.
Thanks!
Replies
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There are many modules in the market that allow transmit signals few feet away but such devices usually are designed for data transmission, so an analog signal is not allowed. Your signal is low frequency so may be sampled and converted into digital stream that is possible to transmit with a simple Bluetooth module. In the other end the digital stream has to be converted again into an analog signal and amplified up to desired level.
RS supplies Bluegiga modules that may solve your transmission problem and there is one of then that includes analog voice transmission capability that may be enough for your application.
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Well, it depends on how far "a few feet" is, but it may be possible to use an inductive loop coupling for an audio frequency signal without modulation.
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HI- Short haul 'analog' such as a slow varying DC value, or even speech, can be transmitted without any RF issues. The following method might use a V to F converter (National Semi) where the output frequency represents the varying input value. This can easily be used to drive an LED as either a sharp or broad beam, or, an array of LEDs physically directed towards areas of interest. Photosensors (w/ spectral characteristics similar to your emitter diode) will 'see' your radiated frequency, and will feed an identical IC reconfigured as an F to V. Some trimming for FS gain and near Zero gain will be necessary if accuracy is expected. Also some post-received signal amplification will likely be needed, too. The IC is an LM331 . Similar functionality might also be achieved for a short-short haul using a couple of LM555's. If only one path is needed, one might try IR emitters and detectors(amplified) from old BALL-TYPE mouse devices, but best to use the ones that have the ambient light filtering integrated into the plastic case (look black). Another interesting project might be an adaption of the emitter from a hand-held remote control to drive the modulation frequency and the detector of the donor equipment (such as a DTV settop box) and extract the signal BEFORE it is processed for digital content (as from the remote transmitter). These might be useful where wired connections are not possible, but an optical path can exist.
Have a blast, kwck