I'm looking for some practical advice on a project I wish to undertake: namely, a pair of display and control panels.
Let's say that each display panel will have six LEDs and each control panel will have six switches which will control the LEDs on the opposing panel.
If this is sounding confusing, I'll explain the function.
One control/display panel will be at one end of a building and the opposing panel will be at the other side. The LEDs and switches are mirrored, but the switches on panel A control the LEDs on panel B.
So I'm looking for the following guidance:-
How many wires (or pairs of wires) I will need to run between the two locations to read from the switches and illuminate the LEDs
How best, of the various ways to wire a switch, should I wire my switches? I remember that one can use built in pull down/up resistor on the board to cut down on the need for physical resistors
Given that I want this to resemble an industrial control panel, is there a particular Google search term I could use to find a panel lamp that the Arduino can power?
Will I need to take voltage drop into consideration? There is about a 20m run between the two panels.
There are two ways you could attack the problem. The simplest solution would be to just connect seven wires in each direction (fourteen in total) so you have six power supplies and a common return, and just power each LED from the far panel. With six channels that's getting a bit unwieldy but would still be feasible e.g. using a pair of CAT5 cables. There's no electronics needed, just six switches, LEDs and current-limiting resistors per panel and some wiring between them.
The more elegant solution is to put a controller in each panel and have each one send a serial data stream to the far panel controlling the LEDs. With only six channels the data format in your communication stream could consist of a single byte message with one bit per LED.
20m isn't terrible far. I don't know whether TTL level serial data would be reliable at that distance using simple CAT5 utp cable but it might be - it will probably depend how much electrical noise there is in the environment. It would be worth giving it a try anyway, if you decided to take this approach.
Personally I'd go for the simpler direct wired approach unless you find something unacceptable about that solution.
RS-422 would be the go to do it properly. Using twin-pair (4-wire) telephone wire - or Cat 5/ Cat 6 which is now used as telephone wire, you can also send power (12V to be regulated at the other end) down the line.
You are looking at using a "packet" protocol where a packet contains a synchronising character, a data character or two (either binary bytes with the data bit-mapped, or a human-readable textual-coded message such as "L5+" to turn on LED 5), and a checksum. This gives you increased reliability (you can even include acknowledgements and re-sends) and makes it extensible and able to be logged.
CrossRoads:
Where's the fun in that?
Too much fun I fear - this would appear to be an industrial situation.
