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Design Brief & Approach

A project log for Holst Show Controller

A Teensy based controller board to control a number of motors, plus DMX, RS232 and GPIO.

Chris RobertsChris Roberts 10/24/2016 at 19:520 Comments

The problem this project was aiming to solve was this: how can you automate the control of a number of motors (around 12), DMX lighting and various other devices, based on a schedule that runs over the course of several weeks without any human intervention?

The particular application of this system was for an large installation, which housed a number of motors which drove some elements of a sculpture around at a low speed. The installation also had lighting, controlled via DMX, which needed to change based on the motions of the sculpture. There were to be a number of sequences of motor runs, to change the speeds in a pattern which was interesting for viewers, based on a schedule.

The system needed to be reliable, and run for days and weeks at a time without any attention. It should also automatically turn off overnight.

A number of solutions were considered, with varying degrees of complexity. They boiled down to the following:

PC Based System

A PC running an OS with some custom code could be used to send commands to motors, and with a DMX interface could also control lighting.

Pros:

Cons:

Embedded System

An embedded system could be used to perform the same tasks - including custom designed I/O which meets our exact specs.

Pros:

Cons:

Conclusion

Based on the fact that our needs were fairly specific, it was decided that a better approach would be to design the system from an embedded platform - which we know isn't going to decide to reboot itself in the middle of the night for to updates or something (*cough*windows*cough*), and if it does, then it's our fault :). Also it would alleviate the pain of writing software to interface with a variety of interfaces relying on the OS's selection of drivers, and generally not have to worry about the myriad of other things that go on in a modern PC apart from running our code.

I'll go into more details about the choice of processor in a future log, but this seemed like the best way forward. Or at least a way forward!

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