DMX vs CAN as Control Bus

[FourDee]

I used one from NI back when I did my experiments

[movax]

I used one from NI back when I did my experiments

I looked at their options, very pricey! The Leaf is only $300, so when that gets in I'll see how it works. The SDK looks very easy to use though, which is nice.

[FourDee]

http://sine.ni.com/nips/cds/view/p/lang/en/nid/203384

This one is what I used, also around $300
The NI has a hardware time stamp with 1µs precision, it seems the kvaser only does 100µs but that's depending on your application

[movax]

http://sine.ni.com/nips/cds/view/p/lang/en/nid/203384

This one is what I used, also around $300
The NI has a hardware time stamp with 1µs precision, it seems the kvaser only does 100µs but that's depending on your application

Oops, I looked at the prices with the ~$350 breakout box/connector block included. Now to look into the NI CAN API vs. the Kvaser CANLIB SDK in terms of ease-of-use and language bindings. Did you use LabView when you were working with the NI USB CAN unit, or did you use C/C# bindings?

Any thoughts on the reliability of USB? This installation I think could be installed as a fixture at some point (not actively maintained/monitored), so perhaps a PCI(e)-based unit may be better. If I pick the right API from the start though, it should remain hardware agnostic.

e: It looks like IXXAT makes inexpensive PCIe CAN cards, even based on the same FPGA I'm using at work to implement a few SJA1000s on. Might go with them, if not only to simplify migration if it ends up going USB->PCIe.

[movax]

Began schematic capture on Wed, and decided on using some of CUI's isolated DC/DC switcher modules as my power supplies on-board. Not that important for the MCU, but the isolated 5V supply should be nice and clean for the DAC (DAC is the only 5V component on the board). Still need to wait for KVANT/CT Lasers to fill me on details on the modulation input; all I know right now is that is 0V-5V, but no idea of the effective impedance that input presents to the circuit (i.e. how much current is it going to sink).

[j4cbo]

The impedance on a modulation input is usually 10k-100k, but sometimes as low as 1k. You'll want either a buffered DAC chip or some opamps.

[movax]

The impedance on a modulation input is usually 10k-100k, but sometimes as low as 1k. You'll want either a buffered DAC chip or some opamps.

Planning on the AD5301, which has a buffered voltage output. "High-speed" I2C should be sufficient speed-wise as well. If I turn out to need more precision, the 10-bit and 12-bit big brothers are 100% footprint compatible, which is nice.

Even if the impedance really does drop down to like 1k though, then I think something like the REF195 might be suitable to power the DAC + source current to the input. Since this is a one-off project, cost isn't a huge concern and I could implement a switcher to take 12V down to around 5.2/5.3V and then feed that to the REF195.

[movax]

Apologies for cell-phone pic, didn't feel like pulling out big camera. Boards came in and starting to assemble them... should be exciting to see them in action!

(

e: argh, it flipped the photo :

[movax]

Well, they are (mostly) working, only a few hiccups in terms of design errors! CAN looks halfway decent as well, considering the EMI mitigating parts were all OOS.


Using the DMA engine with CAN, and it's been surprisingly rock-solid. Set up acceptance filters for my messages (only 4; 3 common to every system for brightness + motor speeds, and 1 individual for each system for control) pretty painlessly. I think the dsPIC spends its cycles looping and operating on the values in the DMA Buffer as fast as it can.

Having some issues with Vishao driver though, will post about that in other forum.