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MagicQ and Velleman dimmer kit


Roderick

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I recently built two of the Velleman K8039 dimmer kits.

When I run them from my MagicQ dongle they both irregularly flicker, just little dips at every level.

In test mode they run fine. The LED pars I run from the same DMX feed are fine.

Any suggestions what could be causing this?

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I recently built two of the Velleman K8039 dimmer kits.

When I run them from my MagicQ dongle they both irregularly flicker, just little dips at every level.

In test mode they run fine. The LED pars I run from the same DMX feed are fine.

Any suggestions what could be causing this?

 

Probably the DMX is too "fast" for the dimmer, the dimmer is dropping bytes from the DMX stream and receiving the next channel by mistake. This is a common problem with older design DMX circuits using slow PICs when used with DMX dongles, which tend to bash the DMX out at the maximum theoretical rate.

 

On some dongles you can adjust the timing to add idle time between the bytes, not sure if that is the case on the MagicQ one. If not, there isn't much you can do. You may find that if you put the dimmers at address 1, the problem goes away.

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Assuming by "MagicQ dongle" you mean the MagicDMX interface, rather than the 2 uni USB interface?

 

The MagicDMX should be outputting DMX at 33Hz, with a full 512 byte DMX frame, but doesn't run it up to the timing limits completely and gives a bit of wiggle room between the bytes and between packets. The timing is all within DMX spec though.

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The timing is all within DMX spec though.

 

Indeed, the problem is usually with the receiver not being able to receive fast enough to meet the spec. (I am not singling out Velleman here, I've seen it on various products including things I have designed)

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Hmmmm (® Ynot)

Any smart boxes that could slow down the DMX speed?

I have just tried a Artistic Licence Protocol Converter, improves it a little bit but not completely fixes the problem.

I had been rather looking forward to play with my 'mini' dimmer rack....

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Any smart boxes that could slow down the DMX speed?

Isn't there a 'reduced DMX rate' somewhere in the MagicQ options menu? I haven't got my MagicQ system here in front of me to check, but I'm pretty sure the option is there.

 

Thats a reduced USB rate, not DMX rate unfortunately. Don't ask why its called "DMX rate" ¬.¬ It also only applies to the USB interface products, and not the MagicDMX dongle.

 

Our 4 port ethernet interface supports different DMX timing, but that's the only product that does.

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Hmmmm (® Ynot)

Any smart boxes that could slow down the DMX speed?

I have just tried a Artistic Licence Protocol Converter, improves it a little bit but not completely fixes the problem.

I had been rather looking forward to play with my 'mini' dimmer rack....

There are a few out there, but mostly rather expensive - especially compared to the equipment they would be used to run!

 

If you've got one around, ETC's Net3/ACN DMX Gateways (2 or 4 port) can do this, you can pick four different DMX output rates, and either buffer in one port and out another or send Streaming ACN to it directly over the network from MagicQ.

 

It's a 20MHz PIC so it should be capable of receiving DMX at full-pelt-maximum 44Hz, however I suspect the DMX receive firmware is based on the Microchip App Note AN1076 which doesn't appear to have been written with much reference to the standard :rolleyes: and will not handle any interference on the DMX line at all.

 

I do wonder if somebody has written better firmware for this kit. It's got an ICSP port, so reflashing wouldn't be that hard.

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It's a 20MHz PIC so it should be capable of receiving DMX at full-pelt-maximum 44Hz, however I suspect the DMX receive firmware is based on the Microchip App Note AN1076 which doesn't appear to have been written with much reference to the standard :rolleyes: and will not handle any interference on the DMX line at all.

 

Unoptimised software is my suspicion too. I know some of the software in Velleman kits involving PICs is written in PicBasic which is not very fast.

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Even crude receive code on low speed PICs should be able to receive it fine. I've done DMX reception on an 8MHz PIC before, as all the hard work is trundled off to the UART. It's just the break detect on it that you have to screw around with.
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