Thanks for your great topic. I have the opposite problem to you with too much heat, in Australia.
I have a TFMini connected to a Pro Mini and wired for an I2C port connected to a 3DR PixHawk Mini. All seems clear and I have rechecked a lot. Flashed Pro Mini with your Outdoor sketch and that seemed successful. FC parameters set to:
|RNGFND_ADDR|112 (70 Hex is 112 Dec)|
I have output the 42 57 02 00 00 00 01 06 command to the TFMini.
I have good range output on the TFMini. But I always get 2.55m as SonarRange on Mission Planner or QGC.
I see a square wave oscilloscope signal on both the RX and TX from the Pro Mini to the I2C.
I also have an Airspeed on the I2C which works. I have tried the TFMini without the Airspeed connected - no change on signals or output.
Any ideas on what I have done wrong or need to set,