What radio should I use?
I am making a communication thing where people can send messages and call with their phone, that goes through the arduino and that sends via radio to another one which then receives. The modules will have to be transmitting and receiving, and maybe full duplex for calls, if i can't make it with half duplex. The distance between the modules will be large-ish (~1km). The calls are made with a phone, so it is digitized automatically, so it shouldn't really make sense to send voice in analog (digital also allows for encryption). If the connection would have a low bandwidth, I was looking at maybe implementing the Opus codec. It should also be relatively cheap. Where this would be used there wouldn't be a data connection, that is why i am making this. My current option is the HC12, but it is only half-duplex, and it would be good if there was a way to do two-way calls with it.
There must be clear, unobstructed line of sight.
You seem to be engaging in mostly wishful thinking, so first get a phone to Arduino connection working in your room, and go from there.
It would be mostly unobstructed outside of a few trees, if that counts. If it doesn't, if i get a higher range module, it would decrease it's range through objects, but it should still reach at least 1km.
I already have a few ways of connecting to a phone. I tested bluetooth and i could also use usb otg serial.
That will take some experimental tests, and quite a bit of luck. Be sure to check the applicable laws in your area for unlicensed radio transmissions.
I tested bluetooth
What was the best range you got?
Welcome, Interesting question! You realize your cell phone is simplex. A cell phone is actually a radio with a computer to control it. It is designed to be a one way at a time communication device or half duplex. The switching between transmit and receive happens relatively fast so you may not notice; but if both parties ‘talk’ at the same time only one party can hear the other if at all. It has its own internal codec. It transmits and receives digital packets, not an analog signal.
The HC05 is interesting but it is bluetooth with a top range of about 10 meters depending on conditions. There are COTS (Commercial Off The Shelf) radios available that could do this. A lot depend on what type if licensing you have and your national laws, in the USA it is the FCC. The size of your wallet enteres into this as well.
Around 5-10m, not nearly enough.
It should be legal as long as the power isnt too large, and 433mhz spefifically is completly free. (not really sure about these, but if the walkie talkies are allowed here then i should be able to use that frequency which)
I was talking about the HC12, a radio module
Interesting, then is there a way to use a non root android phone to transmit radio at a reasonable strength and frequency?
I doubt that. In most countries, there are strict regulations on the transmission power and transmission duty cycle in the 433 MHz ISM band, and for every other band where civilian transmissions are allowed.
I suggest to do your homework.
I won't recommend a radio as I am not the designer or a stake holder in the design. You as the design engineer has that responsibility.
I just checked the local law, 433 mhz is allowed for my specific use case.
What else can i use then?
What data transmission rate, in bytes per second, is required? What minimum delay from input to output is required?
Delay doesn't really matter, 8kbps should be enough for sd sound, and 16kbps is preferrable for higher quality calls. Data rate for messages doesn't really matter too, as long as it is reasonable
Really, which part of the World are you in ?
What are the duty cycle and ERP limits that apply, in your area ?
How much experience you you have, of range testing, radio modules that are legal to use, for your application ?
There are some radio modules that might cover the range, but by the sound of it you want to continuous stream digital audio or similar, and in a lot of places in the World thats unlikley to be legal, at UHF at least.
And why suggest an HC12, its just about the worst choice for the application.
Do you have documentation on the digitizing? How does it handle speech pauses? A cell phone system would be insane to not accumulate pause time in a single identifiable value for the pause time.
Interesting.
Good luck.
I will have to implement my own application, so i get to choose the details.
Did you decide not to use the digitized voice data from the phone?
I could but that is not really the point of this. The phone should do calls and messages while the arduino controls the sending and receiving. If there is no other option i could also put a microphone on the arduino, but if i were to send analog data, how would i send messages?