Hi.
I am trying to install OpenWrt on a ZTE router (MF281). I have already disassembled the router. For the installation I use this guide. For communication I use this UART board from Waveshare. I get an output in putty, however I cannot interrupt the autoboot. Is there a specific key combination I need to use?
Any tips are most welcome 
Double-check the UART connections, are you absolutely sure that Rx, Tx and GND are connected correctly?
I have connected the UART board according to the instructions. Seen from the SIM slot GND, Rx and Tx. I get an output in putty, but apparently no keystroke is accepted.
At least other ZTE devices are very picky with the serial used.
Thanks for your comment. Do you have a recommendation which UART device i can try?
I used cheap CP2102-based USB-TTL adapters on my MF282. Just make sure to buy from legit sources, there are counterfeits of these chips AFAIK.
Thanks for your answer. I now ordered a CP2102-based UART board.
The CP2102-based UART board did the trick. Thank you! I was able to stop the autoboot. The router is already flashed and works fine with LTE.
If anyone needs help with this router, let me know 
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Interesting! I wonder what the difference between those uart adapters really is? With only gnd, tx and rx connected there aren't that many variables. Basically only IO voltage and clock stability. And maybe drive strength. Or am I missing something?
Could you measure the voltage on the tx pin of both adapters? A multimeter will do fine. Is there a significant difference?
Sorry for the late reply. You were quite right in your assumption. The voltage for Rx and Tx between the two boards is significantly different.
FTDI232
Rx: 2.53 - 2.55
Tx: 3.34 - 3.35
CP2102
Rx: 3.29
Tx: 3.25
The voltage also seems to be more stable with the CP2102-based board.
Hope this helps
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