Pretty new to arduino and electronics in general but slowly getting there.
My current project aim is to take simple data from the environment and transmit that data through audio on an FM frequency. The data will be integer numbers between 0 and 100. Id like to do this as a way of collecting data from a site that will not have mobile signal, WiFi and out of the range of Bluetooth but will be within the range of a decent transceiver (0.5 - 1km)
My idea at the moment is to have audio files stored and accessible on an SD card. The files will be my voice saying each number in a different file, then depending on the reading the arduino gets it accesses the right file and plays the corresponding audio.
I can do the above but I’m struggling to grasp what it would take to transmit the audio over an FM frequency. I know the limitations of 16mhz clock speed of the arduino. I’ve seen that there are FM modules for arduino but can’t tell if they are appropriate.
Could I build a transmitter separately and then have the arduino control transmission and send the audio file to that transmitter? Is it possible to buy walkie talkies and then have the audio file transmit through them by bypassing the microphone somehow?
Excuse my naivety, RF is such a big field and researching it has gotten my head spinning.
Yes it can be done... only wondering why doing like this ( why transmitting 'as audio' ). You could use an esp32 board ( it include also an 8 bit d/a converter for generating audio ), you don't need the sd, you can store the audio files directly in the flash, connect to your transmitter and you are ok.
You could transmit as 'digital data' and show on a small screen ( easier to do, even able to log the data if needed ), for this approach you can use an esp32 with lora transmitter ( you will find several also with oled display integrated ), used as tx and rx
It is much, much easier to transmit data digitally, using hobby radio modules on legal frequencies.
Adafruit has the best collection of well designed transceiver modules, which have built in Arduinos that can do all the data collection work as well. They run out of the box. Example
What is the purpose of transmitting the audio representation of the number rather than transmitting digital data and then converting it to audio at the receiver?
Doing that legally in the US may require a license. For example, you can't operate a CB or FRS radio legally by remote control. GMRS operates on FRS frequencies and can be remote controlled but requires a license. A GMRS license is relatively easy to get (>=18 years old, US citizen, etc.) and is good for 10 years. Ham radio is an option and if you are a ham, you wouldn't be here asking questions.
Coming up with an DFplayer for the audio should be easy enough.
Finding a FM transmitter (somewhere 88-108MHz) solution will be the thing.
One way or another, unless you become some kind of nuisance, who will know? Perhaps a 'wireless microphone' with a directional antenna pointed spot-on for the receiver. Experiment.
I think the transmitters for playing iPods over the car radio are/were "Illegal" in Inglaterra, but 'everyone' had one.
My mistake. I didn't pay any attention to the OP's screen name. My comments only apply to the US. The power limits of FM adapters for iPods in England is lower than the US.
This is probably the easiest way to do it. You could use a reed relay to close the push -to-talk switch and build a circuit to interface the audio to the microphone circuit.
Thanks for the reply guys, didn’t expect it to get into legal battles but maybe I should have. I will make sure the final set up will be legal. In the UK there are frequencies that are licence free (some 446 frequencies) which I’ll be using to troubleshoot the project.
The main reason for wanting to transmit as an audio is to make use of the transceivers that are already in use, which are standard radios. The screen receiver could be an idea down the line but being able to get the information with equipment that’s already in use just by switching to the frequency would be much easier to implement.
I’ll have a look into the esp32, appreciate the advice.
Yeah, sorry, I did say my knowledge is limited. By FM I meant a frequency that would usually be used by a common transceiver say 400-480mhz.
Bill, thank you, I’ll have a look into them!
I’m in the UK but there are similar laws preventing transmission, although I admit I am ignorant of them at the moment. The reason for transmitting as audio, as I said above, is to make use of transceivers that are currently in use in the project. So without having to implement another receiving device, one could tune to a specific frequency on a standard transceiver and get the data through audio.
Cheers!
That makes sense. Check whether or not your PMR446 radios can be legally remote controlled. One advantage of those is that in the UK, digital transmission is also allowed so maybe that would make an eventual system with other information displayed on a screen easier.
Actually did do this with some cheap walkie talkies, got the push-to-talk working but currently lacking the knowledge to interface the audio output from arduino into the microphone circuit. Any points in the right direction to do that would be awesome as from what I’ve found the voltage output from a microphone is tiny and I’m still trying to learn how to connect/bypass it.