Still Working on my 24 channel DMX Receiver

[David V. Fansler]

Hi DynamoBen - glad to see a section for DMX in the new website. Just a quick update on my 24 channel DMX Receiver - I am still waiting to test all the channels. I have tested 1-24 and a random number of channels up to 511 with success, but want to verify all 511 before I do an “official” release of the design and software. I already have a PCB laid out that is right at 4”x4”. School is about out, and once I get the engine back in the sailboat and get a weeks vacation, I hope to finish testing.
Take care,
David

[DynamoBen]

Perfect, it will be nice to have several DMX project floating around for those wanting to go that route.

Didn't you say you had a built in dimmer curve? I would be interested in learning how you implemented that.

Now all me need is an opto splitter schematic and some more DMX dongles. As far as DMX dongles I have my eye on a DIY project that might fit the bill.

http://www.usbdmx.com/usb_dmx_interface.html

[David V. Fansler]

I did do some work and came up with a linearized dimmer curve that works pretty good for a design I created to take 64 on/off outputs from an Olson 595 and convert it to 8 channels of dimming. I did not implement that in the 24 channel DMX receiver due to a lack of processing time.
David

[DynamoBen]

I don't know that a 24 channel dimmer is worth while.

RS485 (which is what DMX communicates on) allows for a max. of 32 devices on the same line. If you divide this number by the max. number of channels (512) you end up with 16. So really the largest a dimmer would need to be is 16 channels, and then you just chain them together via dmx to get 512.

As far as curves there are several standard curves I just haven't sorted out how to implement them in software yet.

[David V. Fansler]

I chose 24 channels as that was the most channels I could get from a single 16F877 PIC. By implementing 24 channels per PIC, I can reach 512 with 21 units. At 16 channels per PIC it would take (as you indicated) 32 units. So using 24 channels would take 11 less units - and to paraphrase and old saying "Units is money".

[DynamoBen]

Fair enough.

What about power? Thats a fair amount of power being consumed...granted not much more than 16 but still well over 20A.

[David V. Fansler]

I guess I do not see power as a big problem. Since the two available phases are 180 degrees from each other, the zero crossing works for both. Thus you can use however many circuits as is needed to provide the necessary power, without being concerned which 24 channel unit's SCRs are on what circuit. I realize that is kind of a catch all statement. In my case, I am looking at 209 channels, for which most will be a single strand of lights drawing ~1/3A, so a single 15 amp circuit should handle about 50 channels. So if I have five 15 amp circuits, I should be able to provide the needed power to my 209 channels. That is the plan – but we know what they said about the best laid plans and also how a battle plan never survives the first encounter with the enemy!

[DynamoBen]

I stopped by your website tonight and checked out your design. I have to say I really like it. The zero cross sense method and the octals on the outputs are all things you see in professional grade dimmer racks.

Made and progress with it recently?

BTW If you get to the point where you are making boards let me know, I might be interested in getting my hands on one or two. :)

[David V. Fansler]

Hi DynamoBen – Talk about timing – it has been a busy summer and I have not been here since my last post in early June. I decide to check in and there is a message for me! I have not looked at my DMX unit since early this summer. Now that summer projects are winding down (and about time to head back to school), I am about ready to get back to it. Will be glad to share a board or two when done.
Later,
David

[lightingdoc]

If allowed, count me in too! It sounds like you are designing quite a robust system.

DMX seems like a decent way to go. Just wish I could find hardware cheaper than I am seeing now.

[fkostyun]

David, I am interested in this - I want to adapt the ren24 to DMX for next year - and am interested in how the process is going!

[David V. Fansler]

Unfortunately teaching a new class this semester has left me no time at all to work on my DMX system. Hopefully early next year I will have the time to get back to it.
Thanks,
David