Lesson Learnt - Pixels wiring

N

nzlongfellow

Dennis from NZ
Joined
Jan 2, 2014
Messages
538
Location
Lepperton, Taranaki
Had trouble with irregular display.
Thought it was my splitter modification.
I have 10 large circles and had fitted a "T" splitter between them to get up to max pixels in universe.
Each circle has a 4m lead from the splitter to the first pixel. Maybe pushing the distance but worked OK for a single model but of course the signal to the next model in line has to travel UP 4m then DOWN the next 4m, thus 8m between pixels.
Time for this Kiwi to install a null pixel at the start of each lead.
Lesson learnt.
 
Don't need a null pixel ..... just use thicker wire (for both data and common)... then you can bridge distances of more than 20m (I've tested using 12AWG 12V garden wire, haven't found the limit, 15m is far enough for me, but I think I tested more than that. The voltage drop was negligible.) And that is using the 12AWG over the distance, but it is connected to 18AWG pigtail connections. totalling about 2.5m on the ends.
 
Wow, so you can get 15m plus between pixel elements with 12AWG wire. I guessed that voltage drop would be minor but didn't realise the data would stay good over that distance.
 
Only reason the data degrades is because of voltage drop.

A 0 is zero volts and a 1 is 5 volts. Voltage drop caused by resistance affects the + and the common.

Because the common is not earthed, our 0V will rise to 0.5V and our 5V will drop to 4.5V for example over long distances. This gets worse the longer you go, until eventually in extreme cases you would have close to 2.5V on both. This makes it hard for the chip at the other end to decipher what is a one and a zero.

Basic rule to remember, The bigger the cable, the lower the resistance of said cable, and the less voltage drop you will have, leaving more voltage available for the equipment attached to the cable.

Cheers,
Rowan
 
The data also degrades due to wiring capacitance. So whilst a really good common (0V / ground) is important, it's not the only determining factor in data integrity, especially for high speed data.
 
Got rid of the long leads and just put plugs at the starts of the displays for now. All good with lights. Need some heavy cables to and from each one now.
 
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