Hi
I am starting a project which will have a single controller unit with several wireless sensors. Pretty much like a wireless burglar alarm.
First question is regarding the wireless sensors. I have ordered some ICStation RF 433 MHz transmitter/receiver module kits like these.
I have watched this excellent series of XBee tutorials.
I basically want to achieve what is done in those tutorials i.e. assign an id to each sensor and have it communicate with a single receiver which will also log the data received.
So far the only tutorials I found for (cheap) RF 433 MHz modules are very basic and just cover establishing communication. I am looking for something more in-depth like the above tutorials.
Any links or info would be most welcome and appreciated.
Upon further research it seems the modules I had in mind do not have an ID.
Is anyone who has had experience with the Hope RF modules prepared to share?
A broader over view of the project is is as follows :
The central unit will be an Arduino, with SD card datalogging for at least 50 sensors.
Sensors will be battery powered "Ardunios on a PCB".
Sensors will transmit signal to central unit on detection + plus report status on daily basis i.e. ok or low battery.
Central unit will post latest recorded data to web site (MySQL database) at regular intervals - say every 4 hours.
Central unit will query sensor if no daily report received - this probably means a transceiver rather than just a transmitter at sensor.
It would be nice if system could operate as a standalone i.e. no PC required.
If possible I would like to use 433MHz as distances are quite large and signals may even need repeaters.
I am continuing to research, but I think I might need a mentor on this project - any takers?
You can build an ID into the programs on your slave Arduinos. Simplest way is to have a constant called myID and give it a different value in the program for each device. With a little more programming effort you could have a system where you can input a code and save it to the EEPOM. That would allow you to have identical programs on each slave.
I think you should arrange for the Master to poll each of the slaves in turn to avoid everyone trying to talk at once.
The cheapest arrangement is to have the sensors be transmit only, and transmit data infrequently (possibly at random time intervals), so the transmissions rarely overlap. Use VirtualWire for this. You will lose some data when transmissions do overlap, but that situation can be detected if each message also contains a record ID, which increases sequentially with each transmission.
Learnt quite a bit more from my research.
To speed up development I am still looking for a collaborator/mentor.
Or.. anyone offering design/prototyping as a service?
No offers so I guess I am going to have to do this the tough way :-[
I have ordered the HopeRF RFM69W and RFM69HW models for testing - all are transceivers.
The implementation will be to "encode" each sensor with a unique id/code. The host station must learn the codes of each sensor associated with it, so it only listens and records the signal from its associated sensors. The sensors will transmit only when the sensor it is "tripped" e.g. motion is detected. The host will once per day poll each sensor and record the battery status. All signals received by the host will be written to an SD card.
I am wading through the RFM module data sheet and my first question is regarding modulation.
There is a choice of FSK and OOK. Is there a particular advantage in using one or the other for my application? Or maybe which is easier to implement if there is no distinct advantage?
Repeaters will be used for longer distances.
In figures 33 & 34 on page 52 the packets can accommodate an optional "user defined" (Node ID) address byte.
In table 28 on page 72, there is reference to a node address.
Am I correct in assuming the node address (pp72) is the Node ID (pp52) as defined by the user?
Has anyone been able to encode one of these RFM modules with a unique ID without resorting to including the node id in the code? or any suggestion how to?
Otherwise I guess this is may be a question for HopeRF.
Wallwart is wall powered AC/DC power source. Replace with battery for portability.
2-way RF, or 1-way? What range?
Would be pretty simple to mount nrf24L01+ module or a 315/433 MHz Rf module on a card with sensor and battery contacts, maybe add a battery charging circuit.
What kinds of sensors are on them? Battery charge circuits? Other hardware changes to minimize battery current consumption? All that stuff is where customization comes in.
