octows2811 basictest color issue

[qtong]

Hi everybody,

Just to do a quick introduction, I am a COMPLETE beginner when it comes to electronics/programming outside of my freshman engineering electric & magnetism class and some basic C and matlab in some math classes. I recently bought a pi, a few teensy 3's, a ton of leds and started to play around.

I ran basictest in the octows2811 library and ran into some issues with the output on the leds. All of the colors scroll through perfectly other than pink and orange which scroll perfectly but flash. As soon as it scrolls to white everything is fine again. The problem is only with pink and orange flashing when it displays.

Thanks in advance for the help!

Q

 

[potatotron]

My guess is noise in the wires, and the bit pattern for pink/orange is where the noise is more than the LED controllers can tolerate.

I was only able to get my layout working reliably with both the 220 Ohm resistors and the 74hct245 level shifter. Do you have both of those between the Teensy 3 and the first LED of each segment?

 

[qtong]

My guess is noise in the wires, and the bit pattern for pink/orange is where the noise is more than the LED controllers can tolerate.

I was only able to get my layout working reliably with both the 220 Ohm resistors and the 74hct245 level shifter. Do you have both of those between the Teensy 3 and the first LED of each segment?

I have the 220 ohm resistor but not the level shifter. It sounds like I'll need to pick up some of the level shifters and all should be well? I am curious, are they absolutely necessary in this project? I don't recall reading that Paul used 74hct245 level shifters in his project.

Thanks for the reply!

 

[potatotron]

I don't think Paul S did use the level shifters in his demo video board, but enough people have had problems driving the LEDs directly from the 3.3V pins that he included it in the OctoWS2811 library page. My guess is it varies from project to project depending on wire gauges, connection types, etc.

In my case the LEDs worked fine when connected with just the 220 Ohm resistors on my breadboard but 6 of 8 segments had problems on my first PCB prototype. I used an online impedance calculator and it said I should be using ~95 Ohms for my traces so I used 100 Ohm in my second design but still 2 segments had problems. With my 3rd prototype I've added the voltage shifter and now they all blink as expected.

So...the moral of the story as to what value resistors to use and whether or not you need the shifter...it depends...

Good luck!

 

[digital11]

Did you try also putting power at the end of the strip? I've seen that fix any flickering problems I've had with lots of LEDs on one strip. Also try using twisted pair for your signal lines if they're a long run. I was able to run 3 strips per Teensy on 5 Teensy's running on 2 power supplies with no noise and without using a level shifter. If I recall correctly I was using 220ohm resistors for each line, and the lines varied between 2-9 feet in length from Teensy to strip, all twisted pair Cat5e cable with only 1 pair used.

 

[qtong]

Did you try also putting power at the end of the strip? I've seen that fix any flickering problems I've had with lots of LEDs on one strip. Also try using twisted pair for your signal lines if they're a long run. I was able to run 3 strips per Teensy on 5 Teensy's running on 2 power supplies with no noise and without using a level shifter. If I recall correctly I was using 220ohm resistors for each line, and the lines varied between 2-9 feet in length from Teensy to strip, all twisted pair Cat5e cable with only 1 pair used.

What size of wire did you use for power and signal? I do have both ends powered but am using 22 awg solid wire that is up to 4 ft in length. That could be the issue?

 

[PaulStoffregen]

but am using 22 awg solid wire that is up to 4 ft in length. That could be the issue?

It might be.

To test, turn all your LEDs on fully white. Or if you have some software limit where you know you'll always limit the maximum brightness, then turn them all on the whatever the maximum power consumption could be.

Then measure your power supply voltage, at the supply, at the input of each strip, and at the output of each strip. If you can, measure ni the center of a strip. Ideally, you'd like to see between 5.1 to 4.8 volts everywhere. Dropping to 4.6 or even 4.5 might be ok, but if you measure under 4.5 anywhere, then the wires aren't able to handle the current.

 

[qtong]

It might be.

To test, turn all your LEDs on fully white. Or if you have some software limit where you know you'll always limit the maximum brightness, then turn them all on the whatever the maximum power consumption could be.

Then measure your power supply voltage, at the supply, at the input of each strip, and at the output of each strip. If you can, measure ni the center of a strip. Ideally, you'd like to see between 5.1 to 4.8 volts everywhere. Dropping to 4.6 or even 4.5 might be ok, but if you measure under 4.5 anywhere, then the wires aren't able to handle the current.

I tried using the cat5e cable for signal and 16 awg for 5v and ground. Still didn't work, the cat5e just flipped the colors around and larger gauge wire actually made it worst.

So, I decided to move everything within 1ft of the strips and shorten the length of the wire to 6"-12" and everything was perfect. Which brings me to question, how would I be able to make this work with the longer wire?