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Topic: Using a NodeMCU with a 12V WS2811 (Read 5791 times) previous topic - next topic

Paul__B

#15
Jan 29, 2020, 12:36 pm Last Edit: Jan 29, 2020, 12:41 pm by Paul__B
The reference to "LV" and "HV" pins make it unfortunately clear that klrock is attempting to use one of the "bidirectional level shifters" that are specifically not recommended for this purpose (because they are reasonably likely not to work).  :smiley-roll:

You need to use a 74HCT14 or failing that a 74HC04 with two cascaded gates for each channel to perform the level shifting as indicated in #8.  (Unused gate inputs grounded or connected to the same 5 V Vcc as the chip.)

Use one inverter pair to drive each of the two LED strips.



And that was before I looked at his illustration which confirms the error.  :smiley-cool:

klrock

I have tried three different shifters.

1 RobotDyn® 4 Channels Logic Level Converter High Speed Bi-Directional 3.3V-5V

2. KeeYees 10pcs 4 Channels IIC I2C Logic Level Converter Bi-Directional Module 3.3V to 5V

3. Geekcreit Bidirectional logic level converter

I also Have a 74HCT125 which I am currently researching how to install.



wvmarle

All three those level shifters are the same type; bidirectional I2C level shifters. They're too slow for WS2811 LEDs.

The 74HCT125 should work just fine.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

Paul__B

The 74HCT125 should work just fine.
But you haven't explained to him how to use it!

At least with the 74HCT14 it is dead simple!

wvmarle

A quick Google search should explain that.

The key is of course the enable pins - they must be held to the correct state (high or low - see data sheet) to make it work. After that, it's just like the 74HC14 without the need of cascading two gates.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

klrock

I used the following:

1 Geekcreit Bidirectional logic level converter
2 Keeyees logic level converter
3 Robotdyn logic level converter

I am also trying 74HCT125 but having trouble understanding pull down requirements.

wvmarle

74HCT125 needs low level on the enable pin to enable the corresponding output. You can just hardwire those to GND, keep the gates enabled. I don't seen where you would need pull-down resistors.
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

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