[PD] physical computing: Lanbox, Arduino, Teleo...? (looking for miditron alternative)

[Martin Peach]

tim wrote:
> Dear List,
>
> We are making installations with moving objects controlled by motors, 
> lights, sound, environmental input.
> The main software is PureData, and the interface we used until now was 
> the Miditron from eroktronix, and a bunch of homebrew relay cards.
> Because of reliability issues we are looking for an alternative.
> The LanBox LCE at first seemed like a good candidate but apparently it 
> doesn't support input signals.
> We need inputs to monitor the position of the objects/motors.
> The LanBox LCX might be a better choice because it has 8 digital ins 
> and outs. (are these also DMX channels?->yes we're DMX illiterate...)
> Maybe DMX isn't the right choice alltogether, is there a beter 
> alternative?
> Is Arduino reliable for example? How about Teleo from makingthings.com ?
>
> A shortlist of what we need to be able to do:
> controlling 3 Motors 220 volt, 25 watt each (left/right, start/stop)
> controlling 3 TL tubes (on/of)
> inputs from 6 end of line switches to monitor the positions.
> input from movement sensor
>
If you're running linux there's the parapin external that lets you use 
the pc parallel port as I/O.
The best way to interface to mains electricity is with a solid state 
relay rated about 5-10 times the actual current you need. The switches 
and movement sensor could probably be directly connected to the parallel 
port, but it's always safer to optically isolate the inputs with 4N26s 
or something similar. This is to limit the damage if any part of the 
system comes into contact with mains voltage or if lightning strikes nearby.
Opto-isolation is the main advantage of MIDI vs. serial (including DMX) 
and USB connections. Others are lower cost and the fact that PD works 
well with MIDI.
Ethernet uses transformer isolation but the overhead of the network 
protocol stack is significant. I would use the Rabbit RCM3700 module to 
do what you are doing. It has all the I/O pins and the development 
software has the TCP/IP stack. Porting basic OSC code to Rabbit was not 
difficult as it's programmed in C. Problem is you have to buy the 
development kit, so although the module is cost-competitive with 
Arduino, if you only want one, it's probably not worth it.
After the parallel port, the Arduino is probably the cheapest method to 
interface the relays and switches, but of course all the methods need 
the same relays and switches.


> In general it should be robust and reliable, preferably no detour via 
> MIDI, so a USB or ethernet based system.

I think MIDI adds a bit of robustness because of the electrical 
isolation in the receiver, but it's probably not that important. Most 
MIDI interfaces these days are USB-based. Ethernet is faster and also 
electrically isolated, but more expensive to implement.

Martin