multi-channel wireless data - RF Cafe Forums

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NOFX30

Post subject: multi-channel wireless data

Posted: Wed Jan 20, 2010 6:47 pm

Lieutenant

Joined: Mon Mar 14, 2005 5:51 pm
Posts: 4

I am interested in sending four channels of physiological telemetry data wirelessly so the information can be monitored in real time. RF transmitters that I have found only allow me to send data from one channel at a time, however, I would like to send all the data continuously. Can anyone suggest a method or RF transmitter IC in order to accomplishing this? Thank you in advance.

fred47

Post subject: Re: multi-channel wireless data

Posted: Fri Jan 22, 2010 11:25 pm

General

Joined: Wed Feb 22, 2006 3:51 pm
Posts: 104

You need to multiplex the data prior to transmission, and demultiplex the data afterwards.

All that "multiplex" means is "combine the signals into a single signal, in a way that they can be separated later". "Demultiplex" is just the separation afterwards.

Since it's physiological data, I assume that it's limited bandwidth. One way to send that kind of data is to modulate an audio subcarrier for each of your four signals. The modulation could be either AM or FM. Each subcarrier would be at a different frequency. For example, you might place a subcarrier at 500 Hz, 1kHz, 1.5 kHz, and 2 kHz. Traditionally, FM is used. The subcarriers are then added, and applied to the transmitter.

The modulation might be done these days with a small microprocessor such as the TI MSP-430 or one of the Atmel ATMini, ATMega, or AT32. In earlier days I might have used a 555 timer chip and a low-pass filter, but that would not give as good performance.

At the receive end, the output from your single-channel receiver would feed 4 bandpass filters (to separate out each of the subcarriers), and 4 demodulators.

Filtering and demodulation would be easiest with a DSP chip - TI's "Piccolo" might be a good choice. TI sells small and inexpensive demo systems, along with a complete development software.

In the "really expensive" category, IRIG telemetry equipment might be used - Google it - but that's probably out of budget range.

Good Luck!

NOFX30

Post subject: Re: multi-channel wireless data

Posted: Fri Jan 22, 2010 11:55 pm

Lieutenant

Joined: Mon Mar 14, 2005 5:51 pm
Posts: 4

Thank you very much for your reply. This is a great idea and I will look into implementing this.

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