Author Topic: Active Pixelnet Output  (Read 1811 times)

Offline davron12

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Active Pixelnet Output
« on: December 19, 2013, 11:24:11 AM »
I'm using the older v1.0 version of the board (without the active/passive jumpers). I have the four MAX490CPA and two 0.1uF capacitors installed, ensured that the IC's have pin 1 in their upper right hand corner, and am getting no signal out of the output jack. Is there something else I'm suppose to do? Right now I'm using a pixelnet/dmx repeater to get a signal to the next board, but it adds noise into the data line. Now that I have everything else in my show working correctly, I'd like to try to fix this problem. I've confirmed that all my boards have this problem, so I'm sure I've done something wrong. I've attached a picture of what my boards look like. Any ideas what I've done wrong or things to check?

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Offline JonB256

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Re: Active Pixelnet Output
« Reply #1 on: December 19, 2013, 02:04:30 PM »
I had the same problem. Talked with David. The fix was to remove the four chips and put "wire jumpers" in my sockets to pass the signal. I did not remove the sockets, just pushed bent resistor leads down into the socket holes, 2 wires per socket only.

It became a Passive output but it does work just fine.  There was some problem with the RS485 chip pinout not being the same as the circuit board design.

Duplicate the jumpering in this picture and it will work just fine.



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Offline JonB256

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Re: Active Pixelnet Output
« Reply #2 on: December 20, 2013, 05:49:53 AM »
Davron - did you get it going?

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Offline davron12

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Re: Active Pixelnet Output
« Reply #3 on: December 20, 2013, 09:13:59 AM »
That will most likely work, as long as it doesn't degradate the signal too much by splitting it. I didn't have a chance yesterday to try that. I spent all night finishing up a sequence for a contest due today. I'll be able to try it this weekend and let you know. That's what I get for being OCD and having to have everything perfect I guess. Any idea if a different MAX IC would work for these boards? You said the pinout was incorrect? I know some of the other MAX chips have different pinouts. Thanks again Jon.

- Ron

Offline JonB256

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Re: Active Pixelnet Output
« Reply #4 on: December 20, 2013, 10:31:06 AM »
David or MyKroft can be more definitive, but what I remember is that the Pinout for Maxim SMD chip is different that the DIP. The board schematic was drawn using the SMD pinout. I've never lookup up the two to see if there isn't perhaps a workaround (like putting the chip in the socket backwards).

As far as splitting the signal, when the Input and Output jacks are that "electrically close" together, it has minimal impact. It is the way virtually all DMX boards work (the Lynx Express has an active out plus a passive out). The RS485 spec is that up 32 devices to be connected in that fashion. How many do you have in that Pixelnet chain? Somehow I doubt you are pushing 32. :) 

In the attached picture, the DIP package is on the top. I think the board is laid out for the bottom one. Not even close.

If you look at the bottom chip, when you install those jumpers, you are connecting "B" to "Z" and "A" to "Y" which would "passthrough" the Data+ and Data- as if the chip wasn't there (which it isn't).

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« Last Edit: December 20, 2013, 10:52:30 AM by JonB256 »

Offline David Pitts

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Re: Active Pixelnet Output
« Reply #5 on: December 20, 2013, 10:50:12 AM »
Thanks Jon for the post. You are exact.

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Offline davron12

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Re: Active Pixelnet Output
« Reply #6 on: December 20, 2013, 02:09:00 PM »
Thank you Jon. No, I'm under 32, so I should be good.

I was under the impression that the MAX490 and ST485 were basically similar except the MAX490 operated at a faster rate, and that even using the MAX490 we were limited to 32 boards. I guess I never stopped to think about how the data was actually flowing on these controllers. The MAX490s on the F16 are actually repeating the data to another bus for 32 other devices to listen and the ST485 is just receiving data for the board, correct?

A question that has puzzled me is why MAX490s are sometimes used and ST485s other times when they look like they do the same thing (besides the pinouts being different). Are the MAX490s used usually when repeating data into another chain because they operate at a faster speed, less latency, and therefore a cleaner signal? It doesn't seem like they're needed for their full-duplex capability. Sorry for getting slightly off topic.

Offline David Pitts

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Re: Active Pixelnet Output
« Reply #7 on: December 20, 2013, 03:01:31 PM »
Thank you Jon. No, I'm under 32, so I should be good.

I was under the impression that the MAX490 and ST485 were basically similar except the MAX490 operated at a faster rate, and that even using the MAX490 we were limited to 32 boards. I guess I never stopped to think about how the data was actually flowing on these controllers. The MAX490s on the F16 are actually repeating the data to another bus for 32 other devices to listen and the ST485 is just receiving data for the board, correct?

A question that has puzzled me is why MAX490s are sometimes used and ST485s other times when they look like they do the same thing (besides the pinouts being different). Are the MAX490s used usually when repeating data into another chain because they operate at a faster speed, less latency, and therefore a cleaner signal? It doesn't seem like they're needed for their full-duplex capability. Sorry for getting slightly off topic.

The MAX490 chips have two dedicated channels. One to receive TTL level signal and produce a differential signal and one to receive differential signal and produce a TTL signal. They both operate independant of the other and at the same time.  To re-buffer a differential signal you simply receive the differential signal which get converted to ttl level output and wire that output to the ttl level input that gets converted back to a cleaner differential signal.

ST485 on the other hand is half duplex meaning they can receive a differential signal and convert to ttl level OR receive a ttl level signal and convert to differential signal. The key word is OR. There are two control pins DE and nRE that determine which direction the conversion is to take place. So these are good to receive or send but not both.


Offline davron12

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Re: Active Pixelnet Output
« Reply #8 on: December 23, 2013, 08:06:19 AM »
Jon  - That worked. Thank you. It took me a couple of days to actually make that change due to the weather. We had snow in November, and now thunderstorms in December. Go figure.

David - Once again, thank you. Yeah, duh, the MAX490 would need two separate duplex channels. What was I thinking? I was thinking there was no need for full duplex, but I wasn't thinking about how it was going to repeat the TTL signal. You basically took the full duplex capability and split it into two half duplex buses. Makes sense to me now.

BTW, I really loved using the F16s this year. So much easier to use than the hubs and SSCs for a megatree. And when I blew a fuse, it took me longer to find a new fuse in my parts than to actually replace it on the board. I can't wait to use these boards for my roof next year.

 

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