I’m looking at using a Teensy 3.1 to run some pixels for the first time (previously only using Atmel 5v Chips) - What’s the go with the 3v logic? Does it still drive the pixels natively or do i need a logic level converter to up the data signal to 5v?
I would definitely go with a logic level converter !
The minimum Vin high level for a ws2812 or the APA102 is 0.7VDD which is 3.5V. That would be typical for most 5Vdc devices.
At 3.3V logic levels, you may still be able to get it working but that is taking a chance !
I figured as much but thought I would check - Thanks.
To be more precise, It Depends.
If you are using sequential output and the microcontroller is quite close (~30cm) to the Din of the strips, you’ll be fine. If you’re using parallel output and/or there is a long data line between the microcontroller and the strips’ Din, you’ll need a level shifter in between.
Note: the 74HCT245 is the only level shifter that is proven to work. The level shifter breakouts sold by Sparkfun don’t (they just aren’t fast enough.)
Thanks for that extra info Robert. In this project the leds would be connected nice and close so it looks like i might get away without using a level shifter which would be nice. Any reason why I could not control about 1.5k pixels?
@Andrew_Huxtable With all due respect to Robert, I would never take that chance. You are thinking of controlling 1.5K pixels and want to cut corners about a level converter !?!?
IMHO… It is simply not worth the potential hassle.
Definitely go with what Paul is suggesting. It is designed to fit perfectly with your Teensy and that will work 100%
If you were driving a few LEDs behind your TV, go for it. But at 1.5k LEDs, it makes no sense not to do it the correct way. Use a level shifter. You’ll thank yourself later.
I’d definitely use one… BUT! just so you know i’ve also managed to use a teensy 3.1 with APA102 and WS2812 type pixels even in largish screens (~250 pixels APA102 and up to 1024 with WS2812) with no level conversion and no problems.
But use one! 
As other people have suggested the 74HCT245 works well, i’ve used this successfully with many types of lights and no problems, very easy to wire too.
Does anyone know if there a smaller alternative chip without moving to surface mount? It’s a pain using such a big chip for only 1/2 data lines . It’s good to have the extras if you want to hook up an ESP8266 wifi module for example but otherwise i’m not keen on the waste! Can a single transistor do a proper job of this for example? I’m not keen on using a voltage divider because they’re a bit rubbish.
The short answer is no.
Thanks for the advice - I think i will just use the level converter anyway. One thing that does confuse me about that though is that i thought that each WS2811 IC ‘cleans’ the signal (timings etc) so I would have thought that if one works, they all would. Have I misunderstood or is it simply the amount of data is likely to introduce errors?
Hi @Andrew_Huxtable , you got it right about the IC regenerating the data (IE: ‘cleaning’) however you still have to be concerned with the data quality provided to that very first pixel !
You are also right about if the first one works, all the others should work.
It is not really the amount of data but statistically if your data is barely at or below the level the 1st device needs it, the smallest amount of noise or crosstalk may corrupt the data to that first pixel.
And for that 1st pixel,
garbage-in = garbage-out
therefore the whole string may get crap !!
If you want something smaller the 74HCT125N works great !
@Pete_Brittain
My jacket is 640 pixels with about 20cm of data line between the Teensy and first pixel and it’s always been fine—I’m also constrained for space in the (pocket-able) controller box so adding a level shifter would be a pain. I think having relatively clean (battery) power also helps.
But as everyone else says, if you’ve got the space and/or there is any significant length in the signal path and/or any potential source of interference between the Teensy and the first pixel, use the level shifter.