guidance in 30m arduino wired communication

[hneve]

Hello, I need some guidance with a little project I'm doing for the local theatre, they wish for a remotely controlled motorized curtain. The curtain and the mechanics are in place, and a plan for the motors are sound.

My challenge now is that I could use a form of RF communication, but as this will be a high noise area I belive this to not be a good idea.
There is a xlr multi cable with available spots that I may use, but the stretch is 30m. I have googled and read that the serial communication might not reach the 30m so that is maybe out, I was thinking of trying a audio communication library, like for the 433mhz modules , just cutting out the modules and using the wire instead, is this a bad idea?
I was also thinking about current signalling like 4-20mA but I've never tried this before but it might be an alternative?

Communication speed is not critical, as it only will relay 4-6 button presses to another arduino to control 2 dc motors .

Anyone got a great way for me to get this reliably working ?   

[langwadt]

Hello, I need some guidance with a little project I'm doing for the local theatre, they wish for a remotely controlled motorized curtain. The curtain and the mechanics are in place, and a plan for the motors are sound.

My challenge now is that I could use a form of RF communication, but as this will be a high noise area I belive this to not be a good idea.
There is a xlr multi cable with available spots that I may use, but the stretch is 30m. I have googled and read that the serial communication might not reach the 30m so that is maybe out, I was thinking of trying a audio communication library, like for the 433mhz modules , just cutting out the modules and using the wire instead, is this a bad idea?
I was also thinking about current signalling like 4-20mA but I've never tried this before but it might be an alternative?

Communication speed is not critical, as it only will relay 4-6 button presses to another arduino to control 2 dc motors .

Anyone got a great way for me to get this reliably working ?   

lights are commonly controlled over DMX-512 which physically is rs-485, 30m shouldn't be  aproblem

[dmills]

Seconded, RS485 is simple, standard and an entirely known quantity in that environment.
I might use an isolated receiver to avoid issues with common mode range in the event of a high energy fault elsewhere (Theatres can be nasty for this), use some transient protection and filtering at the receiver.

 If you are running with 24V motors by chance there might be something to be said for actually using DMX (One channel for arm, one to control the tabs) maybe using 4 pin XLR wired for a scroller power supply or a 5 pin DMX connector with separate power (Don't do 3 pin, it is a non standard pain in the arse mainly because there are folks using BOTH of the possible polarities!). 

Another option is MIDI, which has the advantage of being opto isolated by design, and going somewhat slower, but neither one should have any trouble at those distances.

Regards, Dan.

[hneve]

Thank you so much, I see that rs-485 is the way to go.

The motors are worm geared 12V ones. there is hardly any load as the curtains roll very smoothly. there will be endstops for each end for both curtains and they will be driven by GT2 belt and pulleys. 32m of gt2 belt is fun to unravel from a ball.. lol 

So Ill get a box printed with a few buttons and a rs-485 module. I will look into transient protection and filtering along the way.

I was thinking of using DMX also but what i read about it I couldn't really understand how things were controlled.

[Thewafflication]

Check this application note out:
http://www.ti.com/lit/an/snla049b/snla049b.pdf
I found it very handy a couple of years ago.

I have used Cat5E with RS485 at 9600 8N1 baud at 25 yards with no problems.  (Though I never tried any faster, as I didn't require a higher speed.)

Good luck with your project!

[David Hess]

While it is not strictly necessary, I would use optocouplers for galvanic isolation whether needed or not in any industrial environment where high speed is not necessary.

[eb4fbz]

Check RS-422, it's simpler than RS-485 and you don't need a multi drop network. RS-422 is just like a RS-232 over balanced wires. You can use arduino UART and a RS-422 driver/receiver like DS8921 or MAX485/489.

[hneve]

Ok, a little update.
As they use dmx for the lighting control and have free slots on the dmx line, I tested using two channels for controlling the two curtain motors, this worked just perfect.

Only thing I did was implementing a special sequence for the control so that they can not be run unintentionally.
As the dmx protocol sends out a byte per slot the operator needs to first send a 255 and then a 0 before putting the slider either back up too 255 for the curtain to close or approximately around 127 for it to open pulling it back to 0 resets the lock and should the operator push the slider past 220 while opening it will reverse.

I tested this and it only needs a fraction of a second to unlock so I belive I have secured the operation from unintentional use as good as I can. On this manual slider controller this will have to be done manually but on a pc controller (that I also built,, lol) this can be taken care of by a macro.

Anyhoo thanks for the inspiration guys

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