Buying from AliExpress

[MaxMatrix]

I just posted documentation on that cheap 2-string passive interface board.

Documentation on 2 string passive adapter for $1.56

Here’s a snapshot of the connection expected by the rpi-rgb-led-matrix code. The cheap board appears to exactly match the standard for string 1 & 2. [rpi-rgb-led-matrix Connector Specs]

The sage advice from the 7 year old 3 string passive board docs:

LED panels that have 74HCT245 (as opposed to just 74HC245) in their input stage, can deal properly with the 3.3V logic levels.