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This might be a stupid question, but I can't seem to figure out how to convert 3.3V to 5V with the 74HC14. I have a power source which can supply 5V (see the power adapter at the left), and use it to power the Raspberry Pi and the converter. The Raspberry Pi has GPIO at 3.3V, while the LED strip (WS2812B) operates at 5V. This means I would like to use a logic-level converter to convert the 3.3V from the RPi to the 5V for the LED strip.

Unfortunately, I do not have a lot of experience in schematics, nor can I find any possible location where they use the 74HC14 the way I need it. I could use any help needed!

Design Fritzing Design

74HC14 (from this forum) 74HC14

EDIT 1:
It appears that the 74HC14 does not support 3.3V input, but as suggested by @Justme, the 74LS14 seems to work well. I also found the TXB0108, should that also be useful, or is it better to use the 74LS14?

EDIT 2:

Thanks to the comments section, I stumbled upon the 74HCT125, which might work I've updated the design based on the suggestions, is there anything wrong with it or that could be improved?

New Design

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  • \$\begingroup\$ Here's a work around that allows you to drive more current high or low side. i.sstatic.net/SQuaV.png \$\endgroup\$
    – D.A.S.
    Commented Dec 26, 2019 at 18:59
  • \$\begingroup\$ It worked for me with a 74HCT125E (not HC), which is available cheaply on eBay. A 100Ω series resistor at the output may be required to make it work. \$\endgroup\$
    – Erlkoenig
    Commented Dec 26, 2019 at 19:17
  • \$\begingroup\$ I would rather not use a work around but a solid, stable output that will guarantee it's consistency. I will take a look at your schematic, and also look into the 74HCT125E \$\endgroup\$
    – Mark D
    Commented Dec 26, 2019 at 19:30
  • \$\begingroup\$ I think I found something which might actually work, what do you think? cs5.pikabu.ru/post_img/big/2015/12/22/5/1450770311166023258.png . It is using the 74HCT125P \$\endgroup\$
    – Mark D
    Commented Dec 26, 2019 at 19:36
  • \$\begingroup\$ I've updated my design (see EDIT 2) using the 74HCT125E and a resistor. Did I implement it correctly, or did I forget something / did something wrong? \$\endgroup\$
    – Mark D
    Commented Dec 26, 2019 at 21:41

3 Answers 3

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The 74HC14 does not work with 3.3V logic input when it is powered from 5V. The original schematic uses 74LS14 which does work, and for example 74HCT14 would work too.

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  • \$\begingroup\$ Ah okay, that at least clears some things up, thanks for the tip! Any more ideas / tips you could give me \$\endgroup\$
    – Mark D
    Commented Dec 26, 2019 at 16:29
  • \$\begingroup\$ The output of the 74HCTxx is identical to the 74HCxx \$\endgroup\$
    – D.A.S.
    Commented Dec 26, 2019 at 18:48
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    \$\begingroup\$ The HCT variant recognizes 3,3V as high, but the HC does not. \$\endgroup\$
    – Erlkoenig
    Commented Dec 26, 2019 at 19:18
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Thanks to @Erlkoenig I stumbled upon the 74HCT125N, which I can confirm works very well. Down below is an updated schematic: enter image description here

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I use these light strips all the time. You can power them from the 5v source and used the data line directly from the MCU to drive them. They should work fine. The 3.3v from your MCU is above the logic level '1' for the leds, which is all it needs.

The only precaution is to NOT supply a data line that is OVER the supply voltage to the leds. Meaning you can't power them with 3.3v and run the data line from a 5v MCU.

As a side note, I have found that these light strips will work fine off a 1S LiPo battery without a regulator down to about 3.2 volts, at which point they will stop working. This means you can feed the battery directly to the lights, and then run the battery though a regulator to power your project with 3.3v and connect the MCU data line directly to the lights. That way you can get the maximum current to the lights without worrying about power dissipation from a regulator.

Hope this helps some out...

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