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