AC Dimmer Board
See PIC DMX Development.
The AC Dimmer board is a six channel DMX compliant dimming unit. It has the capability to dim resistive loads up to ~300 Watts (untested), and with modification, much more. Each unit has a hard coded DMX start address and responds to the 6 addresses starting with the start address. The device uses the pinout used on the Philips Color-Kinetics lights, which is considered the "standard" way to pass DMX over RJ-45.
The AC dimmer board was designed for Rush 2011 to control ~35 strands of christmas lights in sync with music. The electrical hardware and firmware was designed by Isaac Gutekunst. The MDF enclosure was designed by Robert Johnson. This device has also been called the "Magic Isaac Box."
A USB to DMX interface was also completed as part of this project. It is a simple FTDI based UART with a RS-485 compliant line driver with an RJ-45 jack. This makes it compatible with the "Enttec OpenDMX" interface, making it supported by both FreeStyler and Q Light Controller. Additionally a small python program was developed for custom control. The python program was mostly a hack to let us control the lights from python. It uses python-libftdi to control the USB-DMX interface. A more usable driver is currently being developed.
The original version was used with success during Rush 2011, despite several design flaws that needed to be corrected before the devices were functional. At least 35 strands, if not more were controlled by two DMX boxes, receiving different frequency sine waves from a python program.
- Ground and VCC were reversed for one input to the PIC. This was fixed by cutting some traces. One set of power supply pins seemed to work.
- INT0 (the first external interrupt pin) did not seem to function (possibly do to problem 1). This was fixed by cutting a trace and wiring it to INT1
- Two outputs to channels 3 and 4 were not working, so as above, rerouted to different output pins
- A lack of terminating resistor made communication difficult at times
- The SHDN (Shutdown) pin on the 485 transceiver was left floating, making for unreliable communication.