Jeremy Harris
Senior Member
With the clocks shifting back recently, I was reminded of what a pain it is going around setting the time on several time switches we have around the house. Years ago I thought of automating this (no one seems to make an affordable radio time code time switch) but have never got around to it. So, having dabbled with RF data links and learned some of the plus and minus points for each, I'm looking for a recommendation from all the many modules out there to suit this task. The intention is to build a master timer unit, incorporating a real time clock that is periodically reset by a radio time code receiver. I already have this working, as I use the same technique to keep a couple of data loggers synced up to the time from an MSF receiver, so would like to stick to the same protocol (mainly because it's already built and just squirts out serial time and date data at 2400 baud). The master timer unit would have the programmed times in for each slave unit and I'm confident I can do this bit OK, with a 4 line display use for programming and status indication of each controlled switch. The idea is that the master unit will transmit data to each slave unit, receive back confirmation that the slave unit has actually switched to the commanded state, and display it, so I can be sure that the slave units are all operating correctly (as least so far as having received a command OK).
Ideally I'd like to use a 5V supply, as that would make life simpler.
The units need to work over a maximum range of around 20m indoors, and I'm not bothered much by the frequency, as long as it's a legal band for low power devices.
I'd very much prefer units that use simple serial comms, with just supply, data in and data out connections, as I don't really wan't to have to faff around using SPI and setting up modules if I can help it.
Price is important, so the cheaper the better to some extent. Each slave module will probably use an 08M2, the smallest 5V supply I can find and a solid state relay, as well as the transceiver.
I need to be able to run at least 4 slave modules, but may well add more in future. I can't see a problem with just sequentially transmitting data as required, with a unique header to identify each slave module in the preamble and the same header used by the slave module when transmitting its response, which would mean I could have a net of lots of units, given the slow nature of the individual command timing. Half duplex would be fine, as slaves will only transmit after they've received a command from the master unit.
I'd rather not use pairs of the cheap and nasty ASK modules, but would prefer a transceiver that has a modicum of error correction built in, so is reasonably immune from interference.
Baud rate needs to be modest, within the range of a Picaxe software serial port, so the cheap 115k baud units that are around aren't really suitable.
I'm not averse to buying from China or that well known auction site, IF I know pretty much what I'm buying. I've looked at some UK suppliers but the prices add up when you're looking to buy half a dozen of the things, plus there aren't many 5V offerings. I could, at a pinch, level shift everything, but it will be a pain having to do it in every slave, as optoisolated SSRs usually need at least 4V to operate reliably.
So, If anyone here has some recommendations for transceivers on either the 433, 868 or 2400 MHz licence-exempt UK bands (and power levels) then I'd be very grateful to hear them. I've spent hours hunting around and getting ever more frustrated at the lack of information available from the majority of sellers!
Jeremy
Ideally I'd like to use a 5V supply, as that would make life simpler.
The units need to work over a maximum range of around 20m indoors, and I'm not bothered much by the frequency, as long as it's a legal band for low power devices.
I'd very much prefer units that use simple serial comms, with just supply, data in and data out connections, as I don't really wan't to have to faff around using SPI and setting up modules if I can help it.
Price is important, so the cheaper the better to some extent. Each slave module will probably use an 08M2, the smallest 5V supply I can find and a solid state relay, as well as the transceiver.
I need to be able to run at least 4 slave modules, but may well add more in future. I can't see a problem with just sequentially transmitting data as required, with a unique header to identify each slave module in the preamble and the same header used by the slave module when transmitting its response, which would mean I could have a net of lots of units, given the slow nature of the individual command timing. Half duplex would be fine, as slaves will only transmit after they've received a command from the master unit.
I'd rather not use pairs of the cheap and nasty ASK modules, but would prefer a transceiver that has a modicum of error correction built in, so is reasonably immune from interference.
Baud rate needs to be modest, within the range of a Picaxe software serial port, so the cheap 115k baud units that are around aren't really suitable.
I'm not averse to buying from China or that well known auction site, IF I know pretty much what I'm buying. I've looked at some UK suppliers but the prices add up when you're looking to buy half a dozen of the things, plus there aren't many 5V offerings. I could, at a pinch, level shift everything, but it will be a pain having to do it in every slave, as optoisolated SSRs usually need at least 4V to operate reliably.
So, If anyone here has some recommendations for transceivers on either the 433, 868 or 2400 MHz licence-exempt UK bands (and power levels) then I'd be very grateful to hear them. I've spent hours hunting around and getting ever more frustrated at the lack of information available from the majority of sellers!
Jeremy