[rm30]

The project is interesting, the concept too, the idea of indipendent communication tools also.

I'll tell you a story.

Usain Bolt, the world 100/200m recordman, is not faster than cheeta. He needs a motorbike or a car to be beat a cheeta. But even with a car or motorbike is unlikely is going to overtak a cheeta on the ground of savannah.

This to tell you are thinking about optimizations of a system while you need to choose the right system for the environment.

A 433 MHz based link and a strong modulation is much suitable solution than a BT class 2 device included in the phone.

And here the real hack, most of phones has an integrated FM receiver, higher sensibility than BT, a simple FM transmitter (88-108 MHz) and problem solved.

[deknos]

but for that to work, you need to attach an antenna, no? and where do i get such an FM transmitter? AND android does not support it in the software level, and there's no protocol for the waves?

[rm30]

To have an FM receiver work on a phone, you do need an antenna, the wired headphones serve that purpose perfectly. An FM transmitter is easy to find; you can use the simple 'Jack-to-FM' adapters designed for car radios, or much better, a USB SDR (which can range from a few kHz to GHz).

Regarding the 'protocol for the waves,' you'll need to play with modulation. That’s the fun part. In technical literature, there are many well-defined modulations (like AFSK or FSK) with clear suggested applications for low-SNR environments.

As for Android support, I have no idea. I understand that in this thread, 'free' sounds like 'freedom,' but freedom has a cost. The freedom of communication requires investment: in hardware, software, and the time to learn the physics of the environment.

[deknos]

hm, than i think it's better to use the LORA stuff, no? if i need an external device with my device anyway, i can use one of them.

because the fun thing is cool, but people want some usable...

[rm30]

It depends on which step of the staircase, from pure hardware to pure software, you want to position yourself. Some projects require staying closer to the metal, while others can be purely software. I move up and down this staircase depending on the specific requirements.

If the requirement is to communicate where consumer standards like Bluetooth fail, like in a ship, you have to choose the system for the environment. I evaluate these choices like an architect building a robust system, rather than just using what is available at the nearby shop.