I have bought some of the IC I2C Logic Level Converter Bi-Directional Module 3.3V to 5V and tried them using on WS2812b but they didn't seem to work correctly.
So I just now looked at the circuit diagram and I think why they dodn't...
The HV side needs to be hooked up to 5V and they are seperated by an optocoupler?
But just HV needs to be hooked up to 5V nothing on LV?
And then supply the 3.3V signal at LV and at corresponding HV I should see the 5V signal?

 

Yep. You need a low voltage supply as well.

The signals are buffered by a MOSFET, not an opto-isolator. The circuit works well.

 

Thank you. I read up on it and what I didn't do was connecting LV and HV for some reason. Just LV1,2,3,4 and HV correspondingly. but not LV3.3V and HV5V. I need to try again.