Very Cheap Wireless

Hello All! I needed a way to transmit very simple signals (on or off) wirelessly over a small distance. Thus, i built an AM transmitter similar to this: http://www.instructables.com/files/deriv/FIX/F5B7/A9VEXCFDNXV/FIXF5B7A9VEXCFDNXV.MEDIUM.jpg and hooked it up to the arduino. I then attatched an old am radio to my destination, and I can transmit logic highs and lows, and even some PWM. My next step, get serial working at a nice slow baud rate.

Hope this is interesting!

Wow, cool idea! I never would have thought to try that!

Good work.

Any pictures of the final product?

A similar method was used eons ago in the dark ages of hobbyist robotics (1980's); basically using DTMF encoder and decoder chips, and sending the audio over walkie-talkies. With proper control of the walkie-talkie PTT (push-to-talk) button, and a proper communication protocol, one could get around 1200 bps asynch fairly cheaply. If one wanted to be illegal, one could then run the same thing over a CB radio (I wonder if anyone would even care today?). Then there were the ham enthusiasts running packet radio (completely different beast)...

Hey Check this, it may help you or give you an idea. http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1170901754

Similar to the way the Colorado atomic clock broadcasts the time.

While I always applaud "rolling your own," have you considered the Hope RF modules? Here's a solution that costs less than $10 for an RF link: http://www.open.com.au/mikem/arduino/HopeRF/HopeRF.pdf.

I have a 100mhz oscillator with an on/off pin, so that if I pull it low it will broadcast. I have yet to try using the logic control pin, but my guess is that I will be able to send sound to an FM radio.

I have a 100mhz oscillator with an on/off pin, so that if I pull it low it will broadcast. I have yet to try using the logic control pin, but my guess is that I will be able to send sound to an FM radio.

That would be much more complicated because FM is frequency modulated, not amplitude modulated. Im not sure if an Arduino is up to the task.

Im not sure if an Arduino is up to the task.

FM begins in a range of 65 to 90 MHz (depending on where and when you live) on the dial - do you think a 16 MHz machine would be fast enough to generate such a signal?

:)

FM begins in a range of 65 to 90 MHz (depending on where and when you live) on the dial - do you think a 16 MHz machine would be fast enough to generate such a signal?

Thats besides the point. Theoretically, if this was 100mhz Amplitude Modulated, the arduino could still control the logic pin on the 100mhz oscillator. The problem arises because FM is frequency modulation, which is not possible with an oscillator, because the frequency cant be changed.

good point... Oh well. Do you think the interference caused by an oscillator switching could make sound?

bilbo

That would be much more complicated because FM is frequency modulated

You are correct that FM is frequency modulation (AM is amplitude modulation) At the risk of greatly simplifying how it works, basically the frequency is altered about the actual frequency. If you want to transmit audio, you modulate the frequency with the audio signal, if you want to send High/low, you shift the frequency plus or minus in relation to the High/Low.

There are devices called varicap's which when a voltage is applied, will change their capacitance, and thereby alter the oscillator frequency.

That is of course the most elimentary way to achieve it. Other methods usually involve the phase lock loop that controls the oscillator...etc.

wyager

so that if I pull it low it will broadcast. ..... but my guess is that I will be able to send sound to an FM radio.

When you are not transmitting, you will hear static, when you transmit you will hear quiet. This is like your radio when there is no station on the frequency (static), and when the DJ has forgotten to switch the switch (quiet).

Hope this helps. Mark

My hope was that the really fast jamming and unjamming of the radio station would result in sound... but I guess for that to happen there would have to be a constant white noise or something coming from the station. Oh well. BTW oscillators make great radio jammers, using a ~6" antenna (way wrong for FM) on the output, I was able to jam a radio from like 60 feet.

BTW oscillators make great radio jammers

Yes they do. Depending which country you reside in, there are various rules regarding the amount of power you can transmit, without a licence. This is dependant on the frequency band. ie 433 MHz is for remotes and as long as the power is below xxmW it is acceptable.

You also need to be very careful about what frequency you are actually radiating energy on as well. Sometimes it is not just a single frequency that you are radiating on, and in other cases its the second or third harmonic (ie 2x or 3x). In your case it could be 200, or 400MHz.

With the relatively low cost of the Rx/Tx units for 433Mhz I'm not sure why you would want to go down the 100Mhz route. These devices are already set for data transmision. I have used the low power ones with a 100mm (4inch) wire and can get 200m without any issues. The higher power units with an tuned aerial would exceed that distance.

Cheers Mark