Flickering when using 74HCT245

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sergiidumyk

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Greetings! I've read at Adafruit website that NeoPixels powered by 5v require a 5V data signal, so I decided to try 74HCT245 chip, as they suggest. I connected it, checked that it indeed convert Teensy's 3.3V out to 5V, then connected pin 2 (I'm testing with OctoWS2811's BasicTest for now) to 74HCT245's A1 input, attached 100 Ohm resistor to B1 output and then to DI input of 2812B.

What's even more strange is that flickering is intermittent. Sometimes it disappears, sometimes returns.

When I connect 2812B directly to pin 2, everything works as expected.

I'm using Teensy 3.2.

I know, it would be easier to just purchase OctoWS2811 adaptor, but since I'm in Ukraine I don't want to wait, cause I need to show some prototype to my customer soon.
Why I decided to deal with 74HCT245? Because I wanted to test how many pixels would work from one Teensy's pin. 340 did work, but 350 started to flicker, so I decided to apply all the suggestions from here https://learn.adafruit.com/adafruit-neopixel-uberguide/best-practices

Here is video https://www.youtube.com/watch?v=DDyCrL67RKU

Any clues? Thanks so much!
 
Are the LEDs getting power through those very thin breadboard wires?

I can't see how the power connects in your video. But I can tell you power supply problems or too-thin wires for power are a very common cause of strange flicker problems.
 
I connect positive and ground straight to breadboard from ATX power supply. I know you advised against using such supplies. So looks like it's time to replace it.
I'm just trying to understand why the issue occurs only when using 74HCT245.
Anyways, thanks Paul.
 
Hi guys, I have a similar problem.. but with 3x 74HC595 and 8x RGB-LEDs
.. I have also 8 pushbuttons which are polled through a CD4051.. and when I press one of those, all LEDs flicker short... https://youtu.be/eQFKnv90_SM

is that also a thin-cable and poor-breadboard problem? or could this be a other problem? .. I have read somewhere, that generally one should connect a 10nF capacitor to every voltage input of a IC.. can someone confirm that?
 
AdmiralCrunch said:
is that also a thin-cable and poor-breadboard problem?
Click to expand...

Almost certainly unrelated. Start a new thread and post detailed info, if you'd like help.

With sergiidumyk's LEDs, there are *many* more and they have controller chips inside each LED which receive data. That's a very different setups and it can be very sensitive to changes in ground voltage relative to the chip sending the data.

Your situation is very different. Discussing 2 totally different approaches in this thread is only going to create more confusion than any possibility to help either of you.
 
Just wanted to add that when I switch to genuine Apple 2A power supply and short 30-led strip, the flickering remains, but again only if connected via 74HCT245, so I feel it should be something else that causing the issue.
 
Sounds like to me your powering your teensy by USB and the 74HCT245 is getting its power from that same source? And your LED's are receiving power from ATX? If so you will have flicker. One way to solve this is not use USB for power source on Teensy, instead power the teensy from the same atx power by using 5V. (warning do not power with 12v or magic smoke!). One cause to this is the LED's have use the positive power as the reference voltage. If its not within margin it may not see the signal properly. one way to fix this is to power the teensy from a power source that is more within margin of the 5v signal. Also make sure the ground of the teensy and the ground of the pixels are tied together. Hope this helps....
 
crees said:
Sounds like to me your powering your teensy by USB and the 74HCT245 is getting its power from that same source? And your LED's are receiving power from ATX? If so you will have flicker. One way to solve this is not use USB for power source on Teensy, instead power the teensy from the same atx power by using 5V. (warning do not power with 12v or magic smoke!). One cause to this is the LED's have use the positive power as the reference voltage. If its not within margin it may not see the signal properly. one way to fix this is to power the teensy from a power source that is more within margin of the 5v signal. Also make sure the ground of the teensy and the ground of the pixels are tied together. Hope this helps....
Click to expand...

Thanks crees! Resolved my issue (before reading this) by using another supply, actually Apple charger, just to power 74HCT245. Mu assumption was: since LEDs draw a lot of power, 74HCT245 does not receive stable 5V to function properly and that's causing interruption to Teensy's signal that goes through it.
Indeed, I power my Teensy via USB because I keep reprogramming it and for now not aware of the way to power it from external source and retain the possibility to reprogram it.
So for now ATX only powers LEDs. I feel using 3 power sources is kinda mess but I'll address that later somehow.
 
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