So I have a little project where I want to have lights scattered around the room which can be controlled with arduino`s.
Now I want to be able to do this from a central point, Now of course I need to have a good way to power and do communication between the arduino`s.
I wonder if it would be possible to have 1 single cable which would go from 1 arduino to the next containing 1 power cable, 1 ground and 2 serial cables rx and tx. and use each arduino node as an 'active' repeater so I can kind avoid the problems with having very long cables.
Since I have literally no idea about any of the stuff with cabling and how to best deal with this I would like some advice.
how to best power these arduino`s
wire to use. Can I use just standard wiring and then shield the 4 of them by hand?
the powering of the lights is another problem but optimally I would like to power these from the same wire as the arduino.
if your setup is a master arduino and a lot of slave arduinos, then you probably could use four wires for tx, rx, ground and power between them. You might need diodes on the slave tx pins in such a setup.
Maybe daisy chain like this. Master can include an address, slave receives and passes along if message not meant for him. The slave that finally uses changes the data to "Used" and passes it along, eventually it makes it back to the master.
If the master doesn't see Used after sending a message out, or gets the same message back, it knows there was an error.
If you have to daisy-chain power then use the Barrel jack or Vin, so that the voltage
drop along the chain isn't a problem (unless you use very thin wire or are pulling lots
of current at each node). Thus if you put 10V in at one end and get 8V at the end
of the chain each board can still have a nice steady 5V supply.
This will still mean that the grounds will be at slightly different voltages, but if you use
the Tx -> Rx chain then this won't build up relative to the signals - you need to ensure the
voltage drop along the ground wire isn't more than 0.3V or so, to keep the signals from
going more than 0.3V below ground at the next board (abs max limit).
If the chain can link back into a circle then you can apply power at both ends which
reduces the total voltage drop. For instance if installing boards all around a room this
could be feasible.
Oh yes, one other thing - if you stream serial data from the master continuously with
no breaks then you are at the mercy of system clock differences between the different
boards - many Arduinos only have +/-0.3% tolerance on the system clock so sending 10,000
chars at full rate could cause the sender to get 60 chars ahead, worst case, for example.
This would overflow the Serial RX buffer at some point and lead to dropped characters.
The same issue is likely to happen if you use delay() in the sketch too.
The defence is to not send data at max rate for long periods - though this isn't a
particular common issue I suspect unless streaming lots of data from SDcard or
audio or similar.
Use 115200 as the baud rate everywhere to reduce the chances of saturating the
TX line like this.
