Dmx

I'm looking to design an 8 channel DMX 512 dimmer. I have designed an AC dimmer using PWM and zero cross detector before, and this interfaced to a computer serial port at 9600bps.

However, I'm not sure how I should go about receiving a DMX signal. The first problem is the speed it operates at, but I'm sure it's possible to achieve the required speeds using PBP and a fast enough clock speed.

Secondly, the USART probably wont take a liking to the DMX break and certain other parts of the DMX signal.

If anyone has some fairly complete working code to receive DMX through the USART (I'll be using 16F627) then it would be much appreciated.

If the clock is fast enough, I should be able to keep checking the USART on each cycle of the code, and stop it from overrunning, while still having time to sample for zero crossing and do the dimming.

Once again many thanks!

Matthew

Hi Matthew,

I must admit that i don't know much about DMX, but after looking at this site.......

http://www.proav.de/index.html?http&...ng/DMX512.html

.....it seems possible. 250kbaud 8N2 is possible to achieve with the UART if you stick to an oscillator in multiples of four(4,8,12,16,20) MHz.

I can't answer if the PIC is able to cope with the ammount of data cause i don't know how much it will be.

/Ingvar

I have been developing PIC Based dmx transmission gear with PB but I haven't had much experience with reception but maybe this will help.

I think PB will struggle with speed and getting accurate timing. You will probably need to do the actual receiving of the packet in assembler (This is what I am doing for transmission). At 4MHz one bit = 4 cycles. I don't think the UART will handle the Break/MAB format. Might have to do it directly of another pin.

Let me know how you go.

PS How hard was it to build your RS232 dimmer?

Regards,


Lee Wright.

The RS232 dimmer was easy, the only thing that's holding me back with DMX is the protocol itself. I would use assembler but it's hardly one of my strongpoints :(

Matthew

I know this thread was alond time ago but could you share some information on your rs232 light dimmer\
Cheers