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Choosing the right hardware for transmitting a signal.

Choosing the right hardware for transmitting a signal.

(OP)
Hi Guys
I hope you can help me.
First of all, I´m not an electrical engineer, so I probably don’t understand short terms, and very complicated words etc.
I´m doing a project, where I want to rebuild an insole as a pressure pad – no problem here so far. Then I want to record or even better send the duration of the signal (from the pressure pad, when it´s activated) directly to Matlab for analysis through wifi. I don´t know which components I should use for recording the signal and transmitting it to Matlab. Do you have any suggestions?
It´s crucial that the detection of the signal is very fast so I perhaps can measure a difference in the ground contact time with each step. (For an example, a patient with a new hip alloplastic would have a shorter contact time with the ground on the newly operated leg due to pain.)

Best regards - Kasper

RE: Choosing the right hardware for transmitting a signal.

You need to give us a few more details such as:

Environment - usage indoor/outdoor/both?
Operating range - 1/10/100/1000 feet?
Size - how will the subject patient be expected to wear the transmitter if separate? Do you expect to fit it into the shoe?
Power - how will you power it (batteries obviously) but operating period, disposable or rechargeable, etc? Do these need to fit into the shoe?

You will probably have to design some sort of basic interface circuit between the pressure pad and any commercial wireless device. As to choice of wireless technology bluetooth is a possibility, but range may be limited. The Zigbee standard may be even better as it can be configured for automation and control network with good range. Readily available as simple devices, such as intelligent light switch controllers, smart meters, etc., and can support a whole network of linked devices.

RE: Choosing the right hardware for transmitting a signal.

(OP)
Thank you for your quick reply.
I´m thinking of taking a pretty standard foam insole from at running shoe. Cutting various holes in it, adding conducting material on both sides, and when walking, the connection will occur, and produce a signal. So this part will of cause be inside the shoe. Then i´m thinking I will connect it through wires to a little box I can strap around the patients ankle, with disposable batteries. Each test would probably be like 10min, so the batteries should just be able to last for 10min.
Since this is a prototype it does not necessarily be water resistant etc.
I would like to view the signal live on my pc, and the range would not be more than 30m tops. I could probably do the tests on a treadmill, and the the distance would be minimum. Otherwise it would be ok, just to record the signal and import it afterwards.

I have to check up on Zigbee, since I dont know what that is. I have read about Arduino boards, and there wireless shields, but I´m not sure if its overkill?

RE: Choosing the right hardware for transmitting a signal.

More common practice in the biomedical world would be to use a simple, analog, RF transmitter.

The analog signal of interest might be modulated directly onto the carrier, or it might have to be converted into a proportional-frequency audio 'subcarrier' tone first. This choice is dependent on the spectral range of the signal of interest. You'll probably need the subcarrier audio tone for a low frequency pressure signal at walking gait frequencies. The RF would normally be a low power signal in one of the unlicensed bands (e.g. 900 MHz). The receiver would convert the RF back to analog (or just capture the frequency of the subcarrier tone). This is then interfaced into the PC using an off-the-shelf analog input card or USB device.

One could use more modern digital techniques (e.g. wifi), but they'd be far more complicated, much larger and need a much larger battery. If somebody offers an integrated solution, then it would be practical. Otherwise, if you're rolling your own, then it might be a time sink leading to an impractical system.

RE: Choosing the right hardware for transmitting a signal.

It appears you are only sending a binary signal ( ON or OFF )

In that case the job is much easier.

something like this maybe.

https://www.sparkfun.com/products/705

RE: Choosing the right hardware for transmitting a signal.

Uh, no, he hasn't got a binary signal, or an analog signal, yet:

>>> ... standard foam insole from at running shoe. Cutting various holes in it, adding conducting material on both sides, and when walking, the connection will occur, and produce a signal ... <<<

There is much to learn in just that fragment of a thought.


Mike Halloran
Pembroke Pines, FL, USA

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