Wireless sensor network multiple transmitters, one receiver...help
The designs of the transmitters were very small coin cell batteries, motion sensor and RF ( size of a thumb nail) and cheap...
So basically i want to know what kind of rf were used for that one receiver to 0-99 serially coded transmiters...
oh and the motion sensors weren t supposed to act at the same time so there was no "interferences" problem, just needed for the receiver to know from which sensors it came from.
Any ideas ? (and sorry for the crappy english !).
The system almost certainly had all units operating on the same rf frequency.
A transmitter probably started by broadcasting a single burst of carrier wave, as an 'Attention' signal to the receiver.
Then it would broadcast its code number. This might be a series of pulses, consisting of long and short bursts. Binary code, or morse code, etc.
Or it might be an ascii character value.
Or it might be a series of pulses in an amount from 1 to 99.
The transmitters might have their ID code in memory, or it might be hardwired.
What if two units were to transmit at the same time? It would take a lot of work to prevent this. I imagine the receiver ignored both units in that case. However it might be important to detect any motion. So I think each transmitter should be programmed to broadcast an alert every several seconds to say 'I am still detecting motion'.
oh yeah i see...interesting.
I know that in that particular project, the guy could write ID on the transmitter memory from the receiver.
So basically ( if we says that there is no collision from multiple sensors moving at the same time ), if every transmitter hhave the same frequency the only receiver should be able to listen from them all ? Interesting...
It is possible that the central unit transmitted commands to each remote unit. Of course this would require that each remote have a receiver installed. And to tune it. Etc.
It would be a lot of work to hand-craft such a system.
Unless everything is commercially made. Then it would most likely get expensive.
It is entirely possible that the central unit contained scanning receivers, to monitor two or more radio channels.
You are probably aware that the word 'collision' is used in computer networking, because it happens all the time when several devices are trying to get attention. A networking protocol has the job of a traffic cop to make sure all messages have gotten through.
Each remote unit would need some amount of networking capability built in.
Yes, this would be easy if each was on its own individual frequency.
However if each needed a unique ID then that suggests several units shared the same channel.
I think there had to be some way for the remote units to know what their ID was from the very beginning. Otherwise there would be no way for the correct remote unit to know it was the one being told to write the new ID to memory.
A transmitter supplied from a coin cell will preferably transmit only to achieve reasonable lifetime, and thus lack of an synchronization option. In practice, collisions can be avoided by low transmitter duty cycle and pseudo random transmission time. Frequency multiplex and a scanning receiver is possible, but not reasonable for 100 channels.
No requirements for the time behaviour of the sensor network have been mentioned yet, so there are no detail questions I could refer to.
For the transmitter ID, I would primarly think of a factory programmed unique number.