Teensy 3.1 and OctoWS2811 power pretty good but not perfect

[RichardFerraro]

I have built what seems to be a very clean implementation driving 8 rows of 90 led's each.

It is powered by a 30 amp 5 volt supply.
Power/Ground leads are 20 gauge all 10 inches from power supply to start of strip.
Teensy 3.1/74HCT245 5 volt and ground provided from separate wires to power supply
100 ohm resistor on output of 74HCT245.
Signal from 100ohm resister and signal ground provided from Teensy/74HCT245 to each strip.

For the most part, it appears to work.
I see no flickering.
I do observe some (very few) errors in the form of wrong values to pixels.

I have a scope on it and see the +5 volt at the strip and the signal line to have spikes/ringing at the positive edge of each pixel and at the point where the signal would go down if the data was a zero. at 4.56 volts at the strip, I see spike go up to 5.68 and down to 3.52 and a signal ringing from 5.62 to 4.12 with a high level at 4.56.

The ringing dampens very quickly with about 2-3 cycles at a period of 24 nsec.

QUESTIONS:

Is my ringing excessive?
How can I improve it?
Adafruit recommends minimum of 1000uf cap on power input to each strip. Is this advisable?

thanks,

Richard Ferraro

 

[PaulStoffregen]

Is my ringing excessive?

Yes, it looks a bit much.

How can I improve it?

With ringing, the first thing to always check is your scope probe grounding. Many engineers have wasted countless hours on ringing problems only to discover their scope was "lying" due to ground lead lengths or other grounding issues.