@tttadam I think it because there may be values in the read buffer, which are discarded when you init the device. You could try to call tou.read() to flush the buffer instead of re-initing the UART. if that does not work, it's no big harm. Reestablising the UART does not harm.

@Bryan-Hom oh okay thanks for your advice. I only have max485 and max3485 now

@jmpratt Would you mind providing me a link for the hardware you used? I was thinking of using the RS485 library and a 485 to uart breakout board.

Sorry to grave dig, but had I known this earlier it would have been helpful. This post is about the Decagon 5TM, which has two protocols, SDI-12 and DDI. The DDI is typical UART at 1200 baud, which you can read from any UART reader. I've tested it with an FTDI cable and know it works with a LoPy. You do however have to power cycle the sensor to get a new reading. Note: This may not work on new Decagon 5TM sensors if you have changed the SDI-12 address to anything other than 0. Factory default is 0. If you have not used SDI-12 to communicate with the sensor then it should work as expected. We used a mosfet to turn the power on and off for the sensor, controlled by GPIO. Reading the UART within 10s of milliseconds from turning the power on will give you your readings. Its all explained in the integration guide. http://publications.metergroup.com/Integration Guides/18237 5TM Integrators Guide.pdf I know this doesn't help with SDI-12, but jubbs is using the 5TM specifically, which has this dual protocol stack. The sensor was also just powered from 5 volts (same supply source as for the LoPy), the 5TM supports 3.6V-15V, check datasheet for more information including current draw.