Raspberry Pi with rs485 interface

[Michael Sauder]

Hello list,

TLDR; I'm hoping to skip the USB-to-DMX dongles and go directly to an rs485 interface.

 

For my senior culmination project at NY City Tech (Entertainment Technology program) I'm looking to design, build, and publicly document an "all-in-one DMX wireless access point" which will have wireless, ethernet, and at least one DMX port.

Two of the goals of the project are to use cheap, widely available components, and to have everything as integrated as possible. The Raspberry Pi is cheap and widely available. But the various USB-DMX dongles are not cheap, nor are they easily integrated into an all-in-one box. I want the unit to be completely self contained, with no dangly bits.

To eliminate the costly and cumbersome USB dongles, it seems to me that I can adapt a DMX shield from the Arduino camp. At the moment I'm awaiting the parts for this particular shield: http://www.mathertel.de/Arduino/DMXShield.aspx

The Raspberry Pi has two serial ports, as outlined here: http://lavalink.com/2012/04/more-on-raspberry-pi-serial-ports/. I would connect the above shield to the better one.

The questions:

- OLA doesn't appear to have any way of interfacing directly with a serial port. In OLA, I guess this would be a plug-in. Can this be done?

- I searched the archives for "rs485" and came away a bit more worried. Among other things, it seems there may be issues with reliable timing. I'm unclear on what chips fix such issues, and maybe that's why we go through the USB, but still... USB seems an extra step I'm hoping to eliminate. But am I going down the wrong path? Other suggestions for having a reliable DMX port that can be hard-wired onto the Raspberry Pi?

Thanks for any help. You'll be hearing more about this project, as making it "open source" and well documented is part of the whole deal.

Thanks,

Michael Sauder

[Sean Sill]

You won't get reliable timing from the linux kernal. You'll need a microcontroller to act as a smart uart that allows for correct timing of the data. You can then send updates to the device over the serial link if you want, but you'll basically be reinventing what the USB dongles do.

If you want to be really crazy you could try to hack the kernel and add realtime support for dmx to the raspberry pi os image.

[Simon Newton]

What Sean says.

The problem goes back to at least the Open DMX. You just can't rely on
a non-real time host to produce a signal with the correct timing. It
*mostly* works, until it doesn't.

You're not the first person to suggest this. They have been many
people over the last 2 years and they all give up once they realize
the timing issues.

Use a microprocessor.

Simon

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[Andrew Frazer]

What Simon says.

I've been there and tried as well. You'll just end up tearing your hair out.
A small microprocessor is all that is required to do this. The Ardunio sheild acheives because
it is not running a bit general purpose OS.

There is another option you might like to look at; Try looking at a beagle bone, and use its PRU. The PRU ( Programable Real time unit ) is essentially a small microprocessor that is built into the AM3559 Soc.
You'd need to add a differential driver and preferably some optical isolation but it would be easy enough.

For wireless you've got a couple options, the easiest, is just to stick a small usb wifi adaptor in the USB port. ( works well ).

If you come and lurk on our IRC channel you'll find a guy called Matt ( mranstray ) who's got a lot of experience with the PRU's

[Michael Sauder]

On Mon, Jan 13, 2014 at 8:14 PM, Andrew Frazer <andrew...@stellascapes.com> wrote:

I've been there and tried as well.   You'll just end up tearing your hair out. 

Ah, so much for my original idea. I guess there's a reason I wasn't finding anything like it already out there.

 

There is another option you might like to look at;  Try looking at a beagle bone, and use its PRU.  The PRU ( Programable Real time unit ) is essentially a small microprocessor that is built into the AM3559 Soc.
You'd need to add a differential driver and preferably some optical isolation but it would be easy enough.

I actually was originally looking at the beagle bone, but got the sense that it wasn't really active - The BB Black didn't seem to be in stock at a number of places, and many shields haven't been updated to work on the Black. That said, I have a couple questions/clarifications:

- The PRU would need to be programmed, correct? AND an OLA plugin would need to be programmed? Both of those are outside of my current skillset. I've had one (very badly taught) semester of C++, some Ruby and Python experience, and a little bit of Arduino experience. C/C++ hardware programming is a bit down the road for me. (On the road, but distant...). I guess I'm hoping to piece together existing components, or scale back my ambitions.

- By "differential driver" you mean something like a MAX481CPA? And other components from here: http://www.mathertel.de/Arduino/DMXShield.aspx

 

For wireless you've got a couple options, the easiest, is just to stick a small usb wifi adaptor in the USB port. ( works well ).

Easiest yes, especially for prototyping. In my final project I'm hoping to have small external antennas, which presumably would cover a theater space better.

Physically, I'm currently envisioning packing everything into a box similar to the Lil'DMXter (http://www.goddarddesign.com/dmxter4a.html). One or two small swivel antennas mounted on top (swivel so the lid can close). The power cord would also fit inside the lid.  Again the goal - an all-in-one sturdy, portable box that can be taken gig to gig. I'm hoping other people are also interested in such a thing? I'm happy to talk more about it (such as the wireless needs) but don't want to take up too much non-OLA bandwidth.

Thanks!

Michael S.

[Sean Sill]

The BBB is quite active right now. The regular beagle bone is just a bit old I think. Still a good platform.

They do have usb wifi with external antenna connections. That would be your best bet for getting the impedance correct on the antenna.

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Sean Sill
Electrical and Computer Engineering Alumni from
Missouri University of Science and Technology(Missouri S&T)

[Michael Sauder]

On Tue, Jan 14, 2014 at 2:12 PM, Sean Sill <sms...@gmail.com> wrote:

The BBB is quite active right now. The regular beagle bone is just a bit old I think. Still a good platform.

Available is extremely limited right now. Adafruit, Sparkfun, Mouser, Digikey, and several others don't have any in stock. I didn't know if this was because of popularity or phasing out. I'm about to order a "starter kit" from Maker Shed while it's still in stock... 

[Peter Stuge]

Michael Sauder wrote:
> - The PRU would need to be programmed, correct?

That's correct. You program the PRU using a fun and simple assembler
which borrows ideas from a few different architectures.


//Peter

[kultex]

may I give you another idea, which I would find more useful for us here outside:

to port OLA to Openwrt or tomato-usb - I would prefer Tomato because there is nearly no delay

here is the git link for forks 

price for Asus NT 16 and 2,4 GHz is about 60 € with 2 USB Ports.....

price for Asus RT-NT66U with 2,4+5 GHz si about 110 € with 2 USB Ports...

then you have really good WiFi DMX boxes....

[Andrew Frazer]

to port OLA to Openwrt or tomato-usb - I would prefer Tomato because there is nearly no delay

Port OLA to OpenWRT?    - Wow. thats were simon started this thing many moons ago!!

[Andrew Frazer]

Sadly the circuit co guys seem to have trouble organizing themselves to get out of bed in the morning.   They are blaming everyone but themselves for their supply issues!  The beaglebone black is still current and works well. ditch angstrom and install Debian and you'll get ola running in a few minutes. 

There was a dmx out cape design in last years cape contest. It used the Pru.  Add a USB wifi ( you can get detachable antennas and you have a finished project.   Only bit missing is the plugin for ola but it would

Be easy enough.  

--

[Andrew Frazer]

Another alternative for you to look at, although its a little more expensive, is the wand-board   ( www.wandboard.org )..   It runs OLA nicely, has wifi, usb, audio etc etc. 

[Michael Sauder]

On Tue, Jan 14, 2014 at 6:24 PM, Andrew Frazer <andrew...@stellascapes.com> wrote:

There was a dmx out cape design in last years cape contest. It used the Pru.  Add a USB wifi ( you can get detachable antennas and you have a finished project.   Only bit missing is the plugin for ola but it would

Be easy enough.  

I actually arrived at pretty much this setup earlier on on my research. I assume you mean this cape: https://github.com/boxysean/beaglebone-DMX The catch was the OLA plugin. It might be easy enough for you, not so much for me :P I was actually looking at the OLA plugin "readme" when this email arrived. I'm not confident I could do it myself, particularly as I'll be spending much of the semester writing a web-based (and possibly a mobile app) front end for the box.

Just how easy is "easy enough" for an experienced C++ programmer? Is it something that could be asked of someone here? I've no illusions that you get asked such requests often. Timing isn't critical - I can use the "dummy" plugin for testing purposes while programming the front end, a real plugin wouldn't be needed until February, March, even mid April.

Of course, if I'm the only person who would ever use the plugin I might be asking a bit much. 

 

[Andrew Frazer]

The way that Sean did his software was pretty sloppy. The way the memory is accessed isn't very smart. However it's just software.   Dmx out is fesiable but dmx in isn't by the way as you have to implement a soft uart in the Pru. 

--

[Michael Sauder]

DMX out is my priority. DMX in and RDM are down the road, if I continue development after the semester (I see this as a good learning project).

Another thought I had is a BBB/Pi/etc to an Arduino running this library: http://www.mathertel.de/Arduino/DMXSerial.aspx. BBB to Arduino to DMX shield is a bit hacky, but I'd probably eventually consolidate the shield and ATmega circuity onto one board. Or, the combo Linux/Arduino Tre board is supposed to come out this spring. Likely too late for my semester project though. Plugin is still an issue though.

It would seem I'm really obsessed with removing the USB piece... Really I'm trying to avoid the mess of running a cable out of a USB port into a dongle, even if it's all ultimately enclosed in a larger box. I'm going to search for a development board that has accessible USB breakout pins...

[Simon Newton]

I can probably help with the plugin, provided the requirements are
well described and I have a way to test it.

One thing I think there is a market for is a handheld device like
http://www.robe.cz/products/article/rdm-communicator/ but not just
RDM.

Touchscreens for the Pis are cheap now. It would be a matter of
writing a GUI and building a nice case.

Simon

On Wed, Jan 15, 2014 at 9:15 AM, Michael Sauder

[kultex]

@mrpackethead  sometimes the first ideas are the best.... and I know Simons first stepps

maybe some more info for arduino, iff you want to keep on this:

http://danlin.de/projekte/arduino-dmx/ - sorry german, but google translator should help

http://playground.arduino.cc/Learning/DMX

http://playground.arduino.cc/DMX/DMXShield

http://www.scenelight.nl/2011/06/19/the-new-rs485-dmx-processor-board/

then some atmega info - based on this howto

http://www.dmxcontrol.de/wiki/Art-Net-Node_für_25_Euro

I have a 2xDMXin/out module with  ATMEGA644P-20AU

I have tested some of this stuff and I would not use it in professional shows - at least at the status a year ago.

for me the best units based on OLA are:

Wlan DMX Box:  Alix1E with a Winstron Atheros card and 4 USB DMX Dongles like DMXKings UltraDMX micro - used in Salzburg Festival this year in Lucio Silla

DLAN DMX Box: Alix 1E or Futro A230 (which you get for 10€) with TP-Link AV500 (15€) and 3 DMXKings (the Futro has only 3 x USB) 17 Units used last year in Salzburg Festival Zauberflöte

I use a ASUS RT-N16  with tomatousb Router and on all units is running the OLA-Live-CD

compared to Lumen Radio, which we have also in Salzburg Festival and is the most professional solution, the DLAN Box has the same delay - the WLAN Box is some msec slower - when both are running on the same Projectors you just can see it. This could be avoided - I think, when OLA is running straigt on Tomato

[kultex]

Ok just in case somebody steps over here, I did some photos and uploaded a  rootfs.gz with the wireless drivers for the Live-CD (atheros + Ralink rt2800usb - ALFA-AWUS036NEH - the Zincom WL0162 which I use is no more available)

Just install the SliTaz-OLA-Live-CD frugal on the CF-Card - rename the downloaded file and change it with the rootfs.gz you find in /boot on the CF-Card

OK - putting here more photos does not work - so I did them also to dropbox

the alix inside  with networkcard ALFA AWPCIO85H

the futro WLAN-Box with Zincom WL0162

the futro inside -the jumper in the right down corner has to be set, to start the futro without touching it

[Michael Sauder]

Nice, thanks!

I had just come around to the idea of using an internal PCI wireless card, and have started looking for Raspberry Pi-like boards with a PCI slot. So far, most of the boards I'm finding seem to be more industrial, with a resulting price jump.

I also was about to respond to this thread saying that I've come around to using a USB adapter and giving up on the rs485 interface aspect (maybe down the road, when I can write it all myself...). For the moment I've settled on purchasing a DMXking ultraDMX Micro - I'll likely attempt to disassemble it so I can have just the circuit board inside of the case.

I'm unclear, however, if the ultraDMX Micro has opto isolation - I don't think it does. Can anyone more familiar with electronics tell me if adding optocouplers to the circuit affects the firmware written to the microcontroller? Or, can you point me to something that has isolation, open schematics and open firmware? I've been looking through the USB adapters listed as compatible with OLA, I'd love to know if, among the open ones, there are any that stand above the others, or that I should stay away from.

Thanks,

Michael

--

[Jason Kyle]

No opto isolation in the ultraDMX Micro. Maybe take a look at the overall system and perhaps you might be inherently isolated anyway. Ethernet is isolated and if your PSU is also isolated then little is gained by isolating the DMX line as well if there’s just a single output. In our higher end products we protect and isolate the DMX line so there’s very little chance of damage even under catastrophic circumstances.

If you only wanted the circuit board for your project contact us via shop.dmxking.com and I’m sure we can work something out. It’s a university project right? Always happy to support students.

 

Best Regards,

 

Jason Kyle

DMXking.com

[Andrew Frazer]

I had just come around to the idea of using an internal PCI wireless card, and have started looking for Raspberry Pi-like boards with a PCI slot. So far, most of the boards I'm finding seem to be more industrial, with a resulting price jump.

You could look at a Wandboard,   You've then got Wireless ( you need to by a dual or a quad ) ,  but they are more expensive, but they pack considerably more horsepower than the PI.     

Are you able to make your own electronics? or are you going to build this up from existing parts? 

I'm unclear, however, if the ultraDMX Micro has opto isolation - I don't think it does. Can anyone more familiar with electronics tell me if adding optocouplers to the circuit affects the firmware written to the microcontroller? Or, can you point me to something that has isolation, open schematics and open firmware? I've been looking through the USB adapters listed as compatible with OLA, I'd love to know if, among the open ones, there are any that stand above the others, or that I should stay away from.

Stay away from anything that does not have its own microprocessor,   i.e. the   ENTEC open and many other variations.    

There are some truly open projects around that emulate an ENTEC interface, but its a question of if you are able to / want to build the circuit.

[Simon Newton]

On Sun, Jan 19, 2014 at 1:35 PM, Michael Sauder <michael...@gmail.com> wrote:

Nice, thanks!

I had just come around to the idea of using an internal PCI wireless card, and have started looking for Raspberry Pi-like boards with a PCI slot. So far, most of the boards I'm finding seem to be more industrial, with a resulting price jump.

I also was about to respond to this thread saying that I've come around to using a USB adapter and giving up on the rs485 interface aspect (maybe down the road, when I can write it all myself...). For the moment I've settled on purchasing a DMXking ultraDMX Micro - I'll likely attempt to disassemble it so I can have just the circuit board inside of the case.

I'm unclear, however, if the ultraDMX Micro has opto isolation - I don't think it does. Can anyone more familiar with electronics tell me if adding optocouplers to the circuit affects the firmware written to the microcontroller? Or, can you point me to something that has isolation, open schematics and open firmware? I've been looking through the USB adapters listed as compatible with OLA, I'd love to know if, among the open ones, there are any that stand above the others, or that I should stay away from.

http://www.openlighting.org/ola/get-help/ola-faq/#What_are_the_recommended_USB_Device_to_use_with_OLA

Simon

[kultex]

did anybody test this unit? - it looks quite well from the pictures

http://www.ebay.at/itm/USB-DMX-512-Interface-Controller-ENTTEC-PRO-COMPATIBLE-/281242145514?pt=UK_Sound_Vision_Other&hash=item417b5692ea

if it works good, it would be a good alternative for European users

[Andrew Frazer]

My only comment is that if they fail to release that 3 pin XLR's are NOT standard, then what other suprizes will there be..  Grrh. Why do we have standards?

[kultex]

@mrpackethead:

 3 pin XLR's are NOT standard, 

I agree with you, but the first you have to blaim is Martin - they started with this shit

@Michael Sauder - what is so interesting with an arm main board - for professional use in a theatre you need professional wireless - I guess - like the Cubietruck has built in WIFI, but how the quality will be compared to a Winstron or ALFA card

the cheapest Arm Board with PCI-E I know is the sabre lite but with 199€ its 2 x so expensive as an Intel-DN2800MT - in Europe I get it for 90 €. If the 

[Michael Sauder]

Thanks for the suggestions kultex. I had looked at the sabre lite, but looking at the pictures it seemed the PCIe connector was a pin header and not the standard PCIe connector? At any rate yes it's expensive and I'd need the wireless PCIe card on top of that.

At the moment the Wandboard that @Andrew suggested looks like it might be a good fit, with built-in wireless (w/external antenna). In a perfect world I'd have USB headers too, but those are rare and not worth the tradeoffs. One day, I hope, I'll be able to design my own custom carrier board for a "system on a module" type unit. I suspect that's a ways off though. And really only worthwhile if this were going in production.

--

[Michael Sauder]

@Andrew - thanks for the Wandboard suggestion. I'm leaning heavily in that direction right now.

As for circuits - I can solder, and piece together electronics from schematics (sometimes with a bit of studying of those schematics...). I would like to learn how to make/design/order my own PCBs, and a small DMX interface module seems doable. However if I can can get the circuit boards for a ultraDMX Micro from DMXking, as @Jason offered, I may go that way just to save time, at least for now.

[Jason Kyle]

It’s not clear this supports DMX In functionality. No RDM support either.

Enttec Pro DMX Out compatible.

 

From: open-l...@googlegroups.com [mailto:open-l...@googlegroups.com] On Behalf Of kultex
Sent: Tuesday, 21 January 2014 00:12
To: open-l...@googlegroups.com
Subject: Re: [open-lighting] Re: Raspberry Pi with rs485 interface

 

did anybody test this unit? - it looks quite well from the pictures

 

http://www.ebay.at/itm/USB-DMX-512-Interface-Controller-ENTTEC-PRO-COMPATIBLE-/281242145514?pt=UK_Sound_Vision_Other&hash=item417b5692ea

 

if it works good, it would be a good alternative for European users

 

--

[Michael Sauder]

Sorry for the multiple emails, but I meant to thank Simon for the FAQ link. I wasn't aware of the openlighting.org website - everything I've been looking at was on opendmx.net.

On Sun, Jan 19, 2014 at 5:54 PM, Simon Newton <nom...@gmail.com> wrote:

http://www.openlighting.org/ola/get-help/ola-faq/#What_are_the_recommended_USB_Device_to_use_with_OLA

[Simon Newton]

On Mon, Jan 20, 2014 at 12:54 PM, Michael Sauder
<michael...@gmail.com> wrote:
> Sorry for the multiple emails, but I meant to thank Simon for the FAQ link.
> I wasn't aware of the openlighting.org website - everything I've been
> looking at was on opendmx.net.

Yeah, I really need to put a banner up on opendmx.net

Simon

>
>
> On Sun, Jan 19, 2014 at 5:54 PM, Simon Newton <nom...@gmail.com> wrote:
>>
>>
>>>
>>
>>
>> http://www.openlighting.org/ola/get-help/ola-faq/#What_are_the_recommended_USB_Device_to_use_with_OLA
>>

[Andrew Frazer]

Micheal, if you are feeling particularly keen, you'll find that the Wand board has on its big edge connector, all the "pins" you would ever need; i.e.;

usb, ethernet, audio etc etc etc..     The EDM connector is stock standard. So if you wanted to design your own carrier board, you could.   The main board will run just by sticking 5V onto it

and you get wireless.      And you can buy those main boards as a stock item.

[Stefan Krüger]

there is another 'mini-linux' thing:
Carambola - http://8devices.com/carambola-2
there is a 'dev-board' with network and usb on connectors. but there is also a pin-header and if you look into the shematics you see the usb also is on there..
here again would be the tricky part to get ola running on this..
for an 'diy' usb dmx thing you can use a arduino leonardo or compatible (the ATmega32U4 is the key) - this uC has build in USB -and has also an UART-
than you can use the marthertel shield design..
as software start you can use the Arduino RGB Mixer :-)
 
my goal is to get this setup to working.. but i think i will get to this earliest at the end of the year 2014...

[kultex]

and I think, that the Atheros WIFI is much better than the the Broadcom BCM4329 of the wandboard and has  a built in FTDI chip - so we are back on porting OLA to Openwrt

http://botdream.com/blog/2013/11/24/setup-openwrt-cross-compile-environment/

http://jeelabs.org/2013/05/06/embedded-linux-carambola-2/

[Peter Newman]

As others have said:

http://www.openlighting.org/first-working-version-of-the-netgear-wireless-artnet-node/

http://www.nomis52.net/?section=projects&sect2=artnet&page=node

[Andrew Frazer]

Beautifully Circular!

[Andrew Frazer]

But its still wifi, and all that entails.  Not sure if i'd ever trust wifi for any 'real' show.   Just too much to go wrong. 

[Ernst den Broeder]

No, you should not.  A crowd of cell phones and other wifi and Bluetooth enabled toys does some interesting things w.r.t. to crowding out the available airtime for communicating at 2.4/5GHz.  It not about signal strength in this environment, it's airtime.  Convention centres, stadiums, lecture halls, etc, all "suffer" from this type of problem.

[Andrew Frazer]

Yes. anywhere there is people, there will be wifi!  Your Experience might be different, but wireless is a technology that i'm just not keen to head down! 

[Michael Sauder]

To be clear, I'm not intending for my unit to be used in shows - at least, nothing complicated or critical. Rather it's meant to be a rugged, portable rigger's remote. (Side question: Why do we call it a rigger's remote when it's for lighting?? hmm..). The box I'm making will be the rugged, portable part. The actual remote interface will be your smart phone or laptop.

In addition, the commands going over wireless will be simple "Dimmer 1 at 50%" in one TCP or UDP burst, not a continuous DMX stream.

[kultex]

but wireless is a technology that i'm just not keen to head down! 

I have used my OLA-WIFI box in Salzburg Festival with 2000 People in the room - no problem - if you use Tomato you just can really block evrything - and just for fun I asked the edv boys to try to hack and disturb - no chance