DMX or DMX512 is short for Digital MultipleX(the number 512 represents the max number of channels), a communication protocol mainly made for lighting controls. It was introduced in 1990’s and was developed by Engineering Commission of United States Institute for Theatre Technology (USITT). On that time, DMX512 is so expensive to design and implement. Only today with the advancement of technology, anyone can now develop their own DMX512 device.
The main IC is FT232RL from FTDI Chip. You can download the datasheet here. This chip is very common and is very easy to find. It is actually a USB UART IC. By the way DMX512 is basically a UART with additional break and start code and converting the level to differential. This means that that instead of using 0V for the low signal, it will use -5V and +5V for high.
The circuit diagram above is from the datasheet of FT232. In case you might wonder, DMX512 is same with RS485 circuit with the DMX512 works only on 1 way communication. The receiver is always a receiver and will never be allowed to transmit data. Because of this characteristic, DMX512 is not recommended for applications where life is at risk because DMX512 has no ability to check errors on the data it receives.
You can further simplify the schematic by connecting the pin 2 and 3 of SP481 IC to VCC since you will only use it in TX mode. Because DMX512 is a one way communication only. SP841 IC can be replace with more popular MAX481 and other equivalent RS485 tranceiver/interface chip.
The problem on the circuit above is that it is not isolated, so when a problem occurs on one of the lights and for some reason it sends a high voltage signal to the DMX line, your computer might get damaged. to prevent this from happening, you can use an optocoupler. The popular optocoupler 4N137 is usually used on this application.
Also Read: DMX receiver using microcontroller