Many of you are familiar with the cheap RF transmitter/receiver pairs available on ebay. The challenges of interfacing with them have been discussed at length elsewhere ( http://www.espruino.com/433Mhz for example). I have yet to trial my AzzyRF protocol on current Espruino builds with compiled JS/etc. I hope to have a chance to do that in the near future, since I think I've settled on a good set of timings (~1250 bits/sec, but 0's are faster than 1's)
However - there is still the issue of the hardware itself. I've been conducting some range studies of these for a paid project I'm working on, and the results have revealed that the price of the module has little bearing on it's effectiveness. Anyway, I thought I'd share my findings on which transmitters and receivers were best (or most of them) with the Espruino community.
The best transmitters are the STX882 ($2-3 each) and - to my overwhelming surprise - the cheap green square ones that are all over ebay. The STX882 performs particularly well at very low (2v) voltages. The LC-technologies SYN115 transmitters are 10-25% behind the top-tier - but surprisingly, the SYN115 transmitters that I made (by copying the commercial design) get very close to the STX882's range, working better than the commercial SYN-115 transmitters. The reason for this is unclear.
In contrast, the cheap green receivers are utter garbage, with a range of 20-50' with 3.3v (results with 5v are not much better, but have not been rigorously recorded, as the project I'm working on is not 5v). I've gotten much better results with the $2 RXB-12 receiver (the little yellow rectangular ones based on the SYN470R - my SYN470R does not perform as well as the RXB-12, despite being a copy of the design, unlike the transmitter); the RXB-8 (larger yellow board, with multiple IC's, a SAW filter and a 10.7mhz bandpass filter) performs just as well, but at three times the price. The SRX882 and RXB-6 (those spiffy looking green ones with the shielding) both have effective ranges 25-40% shorter than the RXB-12.
The overall range I was achieving was ~1250' with the RXB-12 and the best transmitters, all at 3.3v. Line of sight, of course - obstacles make a huge difference.
thanks for the informative write-up!
That's great - thanks! It felt like that here too (I didn't test though) - SYN470 receivers were working well, but the transmitters that came with them were worse than the cheaper ones.
so, what's the best pair?
can you pls help?
and do you mean we can actually mix and match them?
because I got an STX/SRX882 from AliExpress and they don't work (apparently, receiver died either because Gnd/Vcc were swapped by mistake or because of poor quality).
and yes, I got the 'green' kit, which works but not farther away than 10-15 ft, even with additional antennas.
I've just been using the cheap ones shown here: http://www.espruino.com/433Mhz
They seem to work pretty well for me. You should be able to mix and match them too - but the cheap receivers seem to let a lot more noise in, which can make it harder to decode signals reliably on Espruino.
I recommend the RXB12 (the $1.xx narrow ones with the SOIC-16 package on them - all over ebay now) for receiver. Dirt cheap, and performs very well.
Much less difference between the different transmitters than the different receivers, STX882 is good, the cheap green ones are good, and I suspect a few of the other new ones that have showed up recently are also probably good as well.
You can mix and match receivers and transmitters freely.
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