SSC V2 has an output problem (prev - code has a bug)

[MrChristmas2000]

Just received my shipment of 150 ohm resistors.

I will try a few by changing the resistor to 150 to see what happens.

My scope died a long time ago.

[keitha43]

Would we keep the v2 firmware after modifying the resistors just to be clear? Also which would be better the 100 or 150 or would it matter?

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[RJ]

Yes

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RJ

[keitha43]

A new question. If you have a short run to the first node even with changing the resistor and let's say at node 40 you need to have a 4-5 foot run before node number 41, will this be a problem? Or is the ringing only between the first node and ssc v2.

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[chrisatpsu]

to expand keith's question, does the ringing settle down after the first node?

[dowdybrown]

I only had 3 out of 9 version 2012 strings working initially with SSC v2. In my brief testing, switching from 47 ohm to 100 ohm, and shortening the length to the first node to less than 24" made a huge difference!! Thank you Keith and Corey for your persistence in tracking this down. It saved a lot of frustration.

Matt

[n1ist]

Would it make sense to use cat5 between the SSC and the first node (along with changing to a 100R oe 120R resistor)?  The twisted pair in cat5 has about 110R impedance.
/mike

[Corey872]

A new question. If you have a short run to the first node even with changing the resistor and let's say at node 40 you need to have a 4-5 foot run before node number 41, will this be a problem? Or is the ringing only between the first node and ssc v2.

Sent from my Thunderbolt using Tapatalk 2.

to expand keith's question, does the ringing settle down after the first node?

Interesting questions.  From what I see on the scope and experimentally, the answers are:

1) Once the data signal hits the first node, it is cleaned up, amplified and 're-broadcast'.  You can have pretty ratty data into the node and a clean signal does come out.  Though this output is based on what the node interpreted from the input.  So if the data-in isn't interpreted correctly, you have a nice strong, but wrong, signal coming out. (This actually contradicts my earlier thought that the data is just 'piped through', so will try to find/edit that post)

2)  The inter-node distance doesn't seem to have the same problem with ringing.  I have an 8 foot gap set up here on the bench top and, while the signal does show some ringing, it's not nearly as bad as the SSC at even 2-3 feet, and the color changes are still being made 100% correct.  Adding a 47 ohm resistor in that line damped the ringing, too, so I suspect dozens of feet might not be an issue.

I suspect the node input/output is matched for one-another, so not a lot of 'impedance mismatch' and a clearer signal transfer.  Further the node output signal is stronger for some reason...seeing almost 5.7 volts peak between nodes. While the SSC output seems to be about 3.3volt-ish

I won't post here, but this is an album showing some traces:

'perfect' square wave reference, SSC output, 1, 2, 3, 4, and 5 foot intervals along the data line (colors begin to fail at 3 ft), 5 foot interval with 97 ohms to dampen the ringing (colors OK), the data out of the first node, and finally, the node-to-node data at 8 feet.

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So in summary:

The data is cleaned and amplified by the node.  If the first node does a good job, then all is well.

The node-to-node data is stronger, cleaner and less susceptible to ringing.  8 foot transmission seems to be no problem.

[Corey872]

Would it make sense to use cat5 between the SSC and the first node (along with changing to a 100R oe 120R resistor)?  The twisted pair in cat5 has about 110R impedance.
/mike

It's a good thought, but I don't suspect this will work well, and in actual testing it doesn't.  The difference comes down to common mode vs differential mode signaling.  The cat5 is meant to have a +data on one wire and a -data on the other wire of each twisted pair...equal and opposite signals.  We only have a +data, with no equal/opposite, so cat5 / twisted pair doesn't really help us out.

[Corey872]

So if your eyes aren't burnt out after 7 pages, cliff notes to this point:
=================================================

- No evidence of a firmware bug in SSC V2

- No evidence of 'on board' transmission issues in SSC V2

- Data line is susceptible to signal 'ringing' simply due to the physics of sending high speed digital data down a plain copper line.

- SSC V2 is slightly more susceptible due to sinking higher current compared to SSC V1

- Recommend keeping SSC-to-1st node spacing no more than ~18"... even shorter if practical.  At this distance, NO MODIFICATIONS are needed for data transmission.

- If the SSC-to-1st node spacing line needs to be longer, changing the SSC resistor from 47 ohms to 100, 120 or 150 ohms seems to dampen ringing well, and should allow reliable line distances of 4-5 feet.

- The node-to-node transmission is cleaned, amplified and re-broadcast, so as long as the first node in the string can interpret the data correctly, data propagation through the string should not be an issue.

- Node-to-node spacing of 8 feet seems reliable and does not show nearly the ringing as the SSC-to-node line.

- The above listed distances are approximate but should be conservatively safe.  All hardware...strings, nodes, SSC's, wire, etc is expected to have some variability, so your distances for acceptable data transmission may be longer.  If you are experiencing issues which seem to affect the whole string or 'bad first node' syndrome,  give consideration to the data line length bearing in mind the above guidelines.

[RJ]

Yes good summary. I think we need to bring the techno train to a station.

RJ

[smeighan]

A new question. If you have a short run to the first node even with changing the resistor and let's say at node 40 you need to have a 4-5 foot run before node number 41, will this be a problem? Or is the ringing only between the first node and ssc v2.

Sent from my Thunderbolt using Tapatalk 2.

to expand keith's question, does the ringing settle down after the first node?

Interesting questions.  From what I see on the scope and experimentally, the answers are:

1) Once the data signal hits the first node, it is cleaned up, amplified and 're-broadcast'.  You can have pretty ratty data into the node and a clean signal does come out.  Though this output is based on what the node interpreted from the input.  So if the data-in isn't interpreted correctly, you have a nice strong, but wrong, signal coming out. (This actually contradicts my earlier thought that the data is just 'piped through', so will try to find/edit that post)

2)  The inter-node distance doesn't seem to have the same problem with ringing.  I have an 8 foot gap set up here on the bench top and, while the signal does show some ringing, it's not nearly as bad as the SSC at even 2-3 feet, and the color changes are still being made 100% correct.  Adding a 47 ohm resistor in that line damped the ringing, too, so I suspect dozens of feet might not be an issue.

I suspect the node input/output is matched for one-another, so not a lot of 'impedance mismatch' and a clearer signal transfer.  Further the node output signal is stronger for some reason...seeing almost 5.7 volts peak between nodes. While the SSC output seems to be about 3.3volt-ish

I won't post here, but this is an album showing some traces:

'perfect' square wave reference, SSC output, 1, 2, 3, 4, and 5 foot intervals along the data line (colors begin to fail at 3 ft), 5 foot interval with 97 ohms to dampen the ringing (colors OK), the data out of the first node, and finally, the node-to-node data at 8 feet.

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So in summary:

The data is cleaned and amplified by the node.  If the first node does a good job, then all is well.

The node-to-node data is stronger, cleaner and less susceptible to ringing.  8 foot transmission seems to be no problem.

So cool to see the technical discussion and the root causes so clearly shown. Loved the scope pictures!

Great job to all of you.
thanks