Quick question, should I use a 74HCT245 buffer chip using a teensy and LPD8806

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(Owen Brasier) #1

Quick question, should I use a 74HCT245 buffer chip using a teensy and LPD8806 strips. I have added series resistors of 100 ohms directly after the teensy and have never had an issue with fairly long runs (800px) when I inject power from both ends.

I assume I would send the signal and clock through the chip.

I know it works well without, but I would prefer to do things properly. I saw it recommended on WS2811 chips but I couldn’t really find any info on if it was recommended with LPD8806. Are the threshold voltages the same for both? I think I will just add it to try it out but I’d prefer to extract more meaningful knowledge…

(Kasper Kamperman) #2

The Teensy outputs 3.3V the 74HCT245 is a level shifter to 5V. Led strips are typically 5V. So adding the 74HCT245 adds more stability for sure.

But well if you can run without, run without. If your strips are going to behave strange, it probably helps to shift the levels.

I have WS2801 strips that worked well without shifting, but WS2812B didn’t.

(Jon Burroughs) #3

I have a strip of 144 LPD8806’s and I have been using them for months, without a level shifter. I did some posts about it awhile back under the ‘show off your work’ tab of this community.

(Ashley M. Kirchner [Norym]) #4

You can run a strip at a lower voltage. Where you start seeing problems is on a rather long strip where the voltage drop is too much for the far away LEDs to distinguish between a LOW and HIGH signal. It gets iffy with long distances if the ICs are running at 5V but the signal is only 3.3V.

(Owen Brasier) #5

Okay I’ll add it anyway and test it out, my next project will potentially include a 2000px run so I’ll see if I can find what lengths it starts to break down. :slight_smile:

Thanks!