Welcome basti. I would recommended not using that FW image you posted. Use the one linked in this post https://www.communistech.com/blog/forums/topic/new-wifi-bridge/#post-473
The problem with that image is that it uses TCP. If you use the image I linked to it uses UDP. This is much better for two reasons.
1) If you use TCP, iOS decides that the link is a ‘broadband WiFi Link’ and will route all data requests to that access point, this means map tiles will not download. UDP doesn’t have this issue.
2) In a lossy environment the link may become saturated with TCP retry packets. UDP doesn’t have this issue.
I’ll post the info to the firmware as a Support page in the coming days.
I assume you means this Level convertor https://www.sparkfun.com/products/12009
Can you post a diagram?
Thx for posting. 🙂