Simple 4 channel DMX controller

[eggman]

'simple 4 channel DMX controller
'reads 4 potmeters to control 4 lights 
'08-02-08 Kees Reedijk
@ DEVICE PIC16F88, MCLR_OFF, HS_OSC, WDT_ON, LVP_OFF, PWRT_ON
DEFINE  OSC 20             ' 20MHZ crystal
DEFINE  ADC_BITS        8  ' Set number of bits
DEFINE  ADC_CLOCK       3  ' Set clock source 
DEFINE  ADC_SAMPLEUS    50 ' Set sampling time 
DEFINE HSER_SPBRG 4   ' 250 KBaud 

DEFINE HSER_CLROERR 1 ' Clear overflow automatically

RCSTA=%01010000 '9 bit data,usart disabled
TXSTA=%01100101 'Enable transmit, BRGH=1, 9 bit data

PORTA=    %00000000
TRISA=    %00001111		
PORTB=    %00100000
TRISB=    %00000100
ANSEL=    %00001111       
CMCON=    %00000111

DMX           VAR PORTB.5   'DMX output to SN75176 bus driver
level1        VAR BYTE
level2        VAR BYTE
level3        VAR BYTE
level4        VAR BYTE

CLEAR

loop:
    ADCIN 0,level1    'read level potmeters
    ADCIN 1,level2    
    ADCIN 2,level3    
    ADCIN 3,level4    
    LOW  DMX
    PAUSEUS 100
    HIGH DMX
    PAUSEUS 12
    RCSTA.7=1     'usart enabled
    HSEROUT [0,level1,level2,level3,level4]    
    PAUSE 10
    RCSTA.7=0     'usart disabled

GOTO loop

END

[bcd]

Very nice.

One thing to be aware of is the DMX spec says there must be a minimum of 24 channels in a DMX message, so some cheaper devices might not be able to receive the dmx channels correctly.

One option is to send out 20 '0's at the end of the HSEROUT statement.

bill

[skimask]

Very nice.
bill

So, if I understand your comment correctly, this simple implementation really works (aside from the 24 channel minimum that you mentioned) ?

I don't know how DMX works, don't know the actual protocol, never used it, never had a need to use it (can't be too crazy hard as long as a guy reads the protocol documentation thoroughly).
BUT, every once in awhile, about once or twice a year, usually before Christmas, a few new folks log on here, and make a big to-do out of this, that, and the other thing, and can't get a DMX controller to work.
I guess I'm just wondering what the big deal was...after all, if code above works, well, jeeze, that's not so tough...

[Darrel Taylor]

I guess I'm just wondering what the big deal was...

This is the Transmit end of the DMX system.

The "big deal" comes on the Receiving end.
It's struggling to PWM some large number of channels at the same time it's receiving the DMX data at 250Kbaud.

Seems to be a favorite "First Time" project.


eggman,

Short, sweet, and to the point.
Very nice indeed.

[skimask]

This is the Transmit end of the DMX system.
The "big deal" comes on the Receiving end.
It's struggling to Dim some large number of channels at the same time it's receiving the DMX data at 250Kbaud.
Seems to be a favorite "First Time" project.

I suppose it would be a struggle, for the noob, trying to keep the RCREG from overflowing, while performing other tasks.
At any rate, I'm bookmarking it. It may 'only' be the TX end, but reverse engineering some useful RX code doesn't look too difficult.

[charudatt]

This thread code looks goofed up any chances of including a txt file for the benefit of others.

Thanks.

[mackrackit]

Check it now.

[charudatt]

Thanks DAVE.

[aratti]

The vertical scroll bar is missing in the code area! So I can see only the few initial Lines of the code.

From what i understand reading the various Posts, it seems I am the only one with this problem.

Al.

[mackrackit]

Is anyone else missing the scroll bars? I can see them.

[Ioannis]

I see them fine.

maybe is your browser Al. Try some other, Opera for instance. I test it and seems a little faster that IE9.

Ioannis

[aratti]

maybe is your browser Al. Try some other, Opera for instance. I test it and seems a little faster that IE9.

Ok thanks. Problem seems to be with ipad browser, I can see it with firefox.

Al.

[cncmachineguy]

Hi Al. assuming your iPad is like my iPhone, have you tried to "2 finger scroll" in the code window? On my phone I get no bars, but I can scroll the code windows using 2 fingers.

[aratti]

Tank you Bert for the tip. 2 finger scroll in the code window works fine.

Cheers

Al.

[ELZEMEFE]

_Isthissoftwareworks the same wayhserin ?

[ScaleRobotics]

The DMX protocol uses 250k baud RS-485. There are some start pulses and such that need to happen. That what the HIGH/LOW DMX and pauses are doing. Here's an app note from Microchip that explains a bit more about it http://ww1.microchip.com/downloads/e...tes/01076A.pdf

[wagnerandreotti]

What is language? Basic?, C?, mikrobasic? Please help-me! thanks

[ScaleRobotics]

Depends which one you are talking about. The first post example is in PicBasic (check out www.melabs.com for software). The application note example for AN1076 is in assembly: http://www.microchip.com/stellent/id...pnote=en527825

[wagnerandreotti]

thanks!!!!

[comwarrior]

personally... i hate the DMX protocol... but i'm sure their is a reason for it...

running at 250K baud is going to be fun for anyone new...

I recommend double buffering the data and using interrupts both for the USART and the ADC...