what kind of IC/
capacitor circuit can I use to get a clock cycle of 4 microseconds? I would need a
circuit that simply gives a clock pulse output every 2 or 4 microseconds. Thats really the only part that I have no idea about. After that, I could just use some kind of BASIC Programmable IC chip to store lists of
binary commands for controlling a
dimmer. For a kind of test rig.
It's not just putting out
binary data at 250Kbps, but generating the break between packets and the mark-after-break that turns serial data into DMX-512.
I do everything with a little 8031-family microcontroller. Philips has a nice, cheap little chip, the 87LPC762, that does a nice job. The 87LPC762 is a little 20-pin DIP IC with an 8-bit microprocessor, a couple 16-bit counters, a serial port, ram and
EPROM (...and a partridge in a pear tree) all on the same piece of silicon, for under $3. I used it for the internal DMX-512 upgrade I designed for James Lighting controllers.
All the critical timings for DMX-512 can be generated by hooking it up to an 8MHz crystal (80 cents) and setting up the right sequence of instructions.
I believe you can find a link to a shareware assembler for it on the Philips website - along with some sample applications (none DMX-512) and a .PDF of the data
book... or Keil Software has a demo version of their UV2 development environment for programming in C. It does everything my full version does, but is limited to programs of 4K bytes or less (the
EPROM on the LPC family is 2K).
If you want to do more of a real controller, the 87LPC767 adds a 4-channel, 8-bit analog-to-digital converter on the same chip - still in a 20-pin DIP. Use the A to D to read the positions of up to four faders and the serial port to turn that information into a
DMX packet. Uses the same development software and still costs under $4.
String together a couple 4051 analog multiplexers to be able to read more faders and you could easily make a decent 2-scene controller on the cheap.
John