I need a way to transfer small amount of data (4 8bit integers + checksum) over wireless.
I'm struggling to find any information dealing with sending serial transmissions over some sort of radio link. Sending is quite simple, but I have no idea how would the receiving end work, as it needs a clock, which can't be provided over radio.
The second thing is I don't really know which technology to choose for the radio. I'm hoping to build something really really simple and cheap. Range wise i'd be happy with a few meters, say 10, in unobstructed space. Transmission speeds of about 10kbit per second would be sufficient, I think at that speed the bandwidth falls within voice range.
I've built a small FM transmitter before but I have no idea how to make both transmitter and the receiver with a fixed tuning that won't drift when the circuit heats up or the antenna changes shape.
Also I realise that this question is a bit vague, and i'm not looking for finished solution, just some pointers on how to address these problems
Thank you
EDIT: I haven't made up my mind yet. The proposed modules are either more expensive or require more work to set up in the configuration that I want.
What I think i'm going to do in meantime is build a small FM transmitter with two signal generators, each frequency associated with 0 or 1. I can generate the frequency directly from the MCU on the transmitter end. On the receiver I will do a simple freq filter, that should give me 0 or 1 output, I still have to figure out how to clock it though. In the end total parts will definitely be under £1. i'll try to find some material on data transmissions, maybe there is a better way of doing it.
Thanks for the answer Anindo, I will accept if my attempt ends up futile.
Best Answer
For data transmission / reception, one of the less expensive options today is a pre-built module around the nRF24L01+ Transceiver IC. These modules typically offer a built-in PCB-trace antenna, 250 Kbps to 2 MBPS bandwidth before error correction, and are tried and tested.
Most important, they save you time in debugging and antenna tuning. After thousands of people have used these modules, which are built on the manufacturer's reference designs after all, most of the kinks are pretty thoroughly ironed out. Also, being able to tap the experience of many others on the internet who have used such a module, counts for a lot when trying to resolve issues.
For instance, this listing on eBay is for a mere US$2.10 with free international shipping. It uses the 2.4 GHz band, which does not need licensing for low power use in most countries.
Another alternative is this 433 MHz band transmit / receive pair of modules (just 9.6 Kbps though), in case you specifically want to stay with transmit-only and receive-only designs. US$1.99 for the pair makes it pretty attractive.
Of course, in each case, you could as well build your own module starting from the IC manufacturer's reference design, and thus learn while implementing your radio functionality.
It is unlikely that the price advantage of massive volume production can be beaten, though.