# How to make any sensor a wireless one

I am try to build a wireless sensor(right now I am using an adxl335 accelerometer with an analog output) but this project should be general for any sensor that outputs analog. The issue is that I have to first convert the analog to digital to transmit it over RF(I have a 12d,12e RF series which is a four channel Rf transmitter with reciever). But the issue is if I need to convert the analog to digital then I need a microcontroller for the CS as well as clock lines. This just adds enormously to the cost of the project as well as the number of hours I would spend assembling them together and a microcontroller for each sensor does not seem sensible at all. I am wondering what is the general route taken to make an accelerometer or any other sensor that outputs anolog wireless.

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You could choose a sensor with digital output: analog.com/en/mems-sensors/mems-inertial-sensors/adxl345/… – pjc50 Nov 15 '12 at 9:53
Thats precisley what I was leaning towards but the issue is that it is not available anywhere where I live – Developer Android Nov 15 '12 at 12:11
What sample rate do you want? If it's fairly low you can turn an analogue voltage into a time delay between two binary signals. Could you link the datasheet for your RF module? – pjc50 Nov 15 '12 at 14:11
Not a very high sample rate(3-5Khz would be sufficient). The links are rentron.com/Files/ht-12e.pdf and datasheetcatalog.org/datasheets/166/170397_DS.pdf . The RF sensor module I use is something called wx-Tx-01 but I could not find its datasheet – Developer Android Nov 15 '12 at 14:40
As analog bandwidth and resolution requirement vary drastically, there is no such thing as a reasonable universal solution for "any" arbitrary sensor, only solutions for those have certain ranges of requirements. – Chris Stratton Nov 15 '12 at 21:15

It is very common to take an analog signal, pass it through and ADC, into a microcontoller, and out a digital radio. There are many wireless microcontrollers with integrated radios and ADCs for just this task. One example is the mc13224v that's on an Econotag.

The other option would be to transmit the analog signal directly with AM or FM.

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How would I transmit with AM/FM without the help of a microcontroller. Also since I have a large number of sensors spending 55 dollars on each one seems too much to me. – Developer Android Nov 15 '12 at 12:15
You would transmit it by using the sensor output to control the analog AM or FM modulator, or alternatively even to control an audio oscillator driving that modulator - people have been doing telemetry since the dawn of the radio age, long before microcontrollers or even digital systems. Most books of electronic projects will have crude examples. – Chris Stratton Nov 15 '12 at 21:16
I added links to AM and FM transmitters that look like they would be fun to build. – Mariano Alvira Nov 16 '12 at 1:42
Also, the econotag is $55 but the only chip ON the econotag you need is$4 (the mc13224v). There are many wireless microcontrollers with integrated ADCs to choose from. Some are only \$2. Considering all the things you are getting for that package, (the micro, the adc, the low-power sleep modes, and the transmitter and receiver) you can't beat these integrated controllers on pretty much any metric. – Mariano Alvira Nov 16 '12 at 1:46

You may want to consider using RF transmitter/receivers that have an onboard ADC, such as the XBee series (available from https://www.sparkfun.com/categories/111). If all you want is to ADC the analog signal and transmit it, this may be your easiest option.

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You could consider an IR transmitter Receiver link and come up with your own carrier modulation and receiver or multiplex them into one channel depending on accuracy needed and bandwidth for range but must use RF for longer range.

If it is low bandwidth, you can configure an inexpensive TV RF modulator with an analog TV like signal with H sync and analog MUX all the signals using grey as o and black white as peak to peak signal and using a synchronous analog Mux send all the channels in one line at say a 20KHz rate and use a nyquist filter on each channel to prevent aliasing noise. Then use a receiver to DEMUX the analog to S&H buffered outputs Dynamic range will certainly not be as good as digital but 40dB is certainly possible with a good carrier / noise ratio.

With a vertical sync you might be able to watch it on TV. ;)

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