I'm selecting a level shifter for the APA-102 leds.

I’m selecting a level shifter for the APA-102 leds. I know that most people successfully (including me) connected it directly to a 3.3V data pin without shifter. However since I’m designing a PCB it might be smart to keep the official specs in account (Adafruit mentions this also with their Dotstar LEDs).

I know the octal shift registers that work like the SN74HCT245 that is used on the FadeCandy board. However I only need one channel (no more ports available at the RFDuino and APA is fast).

Does anyone have experience with this single channel buffer chip from TI: SN74AHCT1G125 ?

This is what sparkfun have in their 2way level shifter: https://www.adafruit.com/datasheets/BSS138.pdf

(I know it’s an Adafruit doc, but the level shifter I buy is from Sparkfun: https://www.sparkfun.com/products/12009 - they have the full Eagle files - so you could easily pick out the single channel you need).

I tried this Sparkfun breakout, it doesn’t work.

Don’t use the spark fun board - also, remember that for the apa102 you need two channels (clock and data). I think their might be a 4 port version of the 74hct245, but don’t quote me on that.

That said, I believe the “HCT” is the part of the identifier to look for in order to get “fast enough” so what you’re looking at should be good, @Kasper_Kamperman - that said, again, remember you need 2 for the APA102.

The Sparkfun shifter doesn’t work in all situations. @Daniel_Garcia thanks for reminding me that I need two channels for the APA102, I indeed overlooked that. The 4 port version is the sn74hct125d.

@Robert_Atkins doesn’t work, or doesn’t work with LEDs?

It seems to work fine with my Imp

@Mike_Thornbury Doesn’t work for the purpose of shifting the Teensy’s 3.3V output to 5V as input for WS2812B LEDs. If you search on the Sparkfun part number here you should find my longer explanation of what went wrong.

Ok, thanks.

I just bought a bunch for TTL duties, for which they should be fine.

@Robert_Atkins @Daniel_Garcia @Kasper_Kamperman I came across this article for integrating Adafruit WS2812 NeoPixels with the Electric Imp - they suggest using that exact same level shifter I recommended - are they wrong?

Is there something different about the Imp vs the Arduino?

(not attempting a ‘gotcha’ - I am seriously n00bish about all this stuff).

As with running without a level shifter at all, there are plenty of situations where that may work, but may be some situations where they don’t. The 74HCT’s that multiple of us here are recommending are the only solution that hasn’t had any “doesn’t work” situations.


74HCTs it is! and at 20c, it isn’t like it’s a hard sell :wink:

We are using a 74HCT2G17GW-Q100 to shift from 3.0V to 5.0V for APA102. Our software runs on a dsPIC device. There might be a bug in the software but it seems more like a hardware issue with the selected 74HCT. We will probably test the suggested sn74hct125d. If it works I’ll come back and report.

And by the way: we used the sparkfun level shifter too in another project and it didn’t work either. Worked with another 74HCT though.

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