The HC-12 fits what I'm after but cannot find details on whether it will handle RS485 and multiple nodes.
RS485 is a physical serial layer (it's a defined way to transmit serial data over a pair of wires), no radio module will handle that.
According to the documentation I found HC-12 just work in pairs so you cannot used multiple of them.
If you really need a range of 1km HC-12 probably won't fit. The spec says it may reach 1000m if set to maximum output level. This means in an ideal case you may reach 1km with clear line of sight and ideal weather conditions. Under normal circumstances the range will be around 100-200m (WiFi range is up to 300m but usually you get 10-20m, up to 50m if you have clear line of sight).
What limitations do you have (other than the range)? P.e. is power an issue? Do you have control over the whole system (so is the ModBus protocol fixed)?
HC-12 will handle multiple nodes.
You can have 1 to many , but all nodes will receive what is being sent , so there needs to be some way of determining which node the transmission is for.
pylon:
RS485 is a physical serial layer (it's a defined way to transmit serial data over a pair of wires), no radio module will handle that.
Hi pylon, there are plenty of commercially available RS485 serial radios out there for industrial telemetry, I guess what I am asking is there a low cost equivalent available. Dorji do make one for about $25 but it seems that it will only handle a single point to point link only. I'm after multiple nodes. I prefer to use modbus as it is very industry standard and easy to bring the data back to a PLC for further use.
Thanks mauried, yes the radio really needs to be able to extract the slave address out of the modbus transmission so it can be routed to the correct radio.
mauried:
HC-12 will handle multiple nodes.
You can have 1 to many , but all nodes will receive what is being sent , so there needs to be some way of determining which node the transmission is for.
Hi pylon, there are plenty of commercially available RS485 serial radios out there for industrial telemetry,
Excuse me but this is wrong. There may be radios that are able to replace a RS-485 bus and there may be radios that also have an RS-485 interface but it's a common misuse of the term "RS485" to name any half-duplex communication. So please define what your "handle" means. Do you just want to handle half-duplex communication maybe paired with multi-node capabilities or do you really want to connect that to a RS485 bus?
pylon:
Excuse me but this is wrong. There may be radios that are able to replace a RS-485 bus and there may be radios that also have an RS-485 interface but it's a common misuse of the term "RS485" to name any half-duplex communication. So please define what your "handle" means. Do you just want to handle half-duplex communication maybe paired with multi-node capabilities or do you really want to connect that to a RS485 bus?
I apologise for not being technically correct, I am just an industrial electrician and the terms Modbus and RS485 tend to get used interchangeably where I am.
Back to my original question, all I am looking for is a low cost data radio that can handle modbus communication between one master unit and multiple slaves. The radios will handle routing internally and act as a virtual wired RS485 bus.