Electronic – How DMX512 protocol da daisychain

I'm doing that very thing in a project I'm working on right now. I can't take credit for this, but it sure has worked well.

Both the MAX485 and MAX481 should work well. I modified this design a bit. This design currently has a 133ohm terminating resistor between pins 2 & 3 of the DMX connector. This is used to terminate the end of the dmx bus. I added a switch so that I could enable or disable the terminator.

You'll also note that a DC/DC converter is used to create isolated supply and ground. I'm sure someone else can explain, in better detail, why this is important. My understanding is that it helps with ground loops and voltage differences with the external devices that are connected to the dmx bus.

DMX Shield for Arduino with isolation

You need:

1. 512 channels of high-current PWM driver;
2. Some means of configuring any/all of the channels on the fly;
3. Some means of communicating with the configuration device.

If you can find a multi-channel high-current PWM driver with a serial control interface then that would be a good start (because you could eliminate the FPGA's). Failing that, to me, the solution is:

1. 512 channels of open-collector/-drain driver, either as individual drivers or as multi-channel units.
2. An FPGA (or a collection of FPGA's) with at least 512 output pins to provide your PWM, and possibly fade logic.

3. A reasonably powerful MCU with an Ethernet interface and an external memory bus that you can use to map the PWM control registers in the FPGA/s directly into MCU memory for easy access.

   • An ARM Cortex-M3 or M4 with the necessary peripherals would be ideal, e.g. the STM32F407 in a QFP144 package, plus supporting circuitry including an Ethernet PHY and magnetics.
   • A collection of Xilinx XC6SLX4's in QFP144 package for the FPGA's; you'd need at least 8, plus supporting circuitry.
   • Drivers will cost; your current and voltage requirements are non-trivial so you will pay through the nose. Bear in mind how much heat those drivers will generate, too; cooling will not be optional.
   • Last but not least, the power supply. This is what will really hurt: 512 channels at up to 500mA each is 256 amps @ 12V. That's over 3kW of power. If you try to low-side the spec on the power supply (to 512*0.2A i.e. 1.2kW) then sooner or later it will let you down, so don't do it.

In short, this is a sizable design project that, particularly as a one-off, will cost quite a bit of money (at least $750 in parts, excluding the PSU and circuit boards). You would also have to program it to do what you want.