Connecting Bare Wire Sensor to Jack Adapter

For a Meter Hydros 21 sensor, check the manual that came with the sensor to double-check that they haven’t change the wiring colors lately, but the usual pattern is red is data, white is power, and black is ground.  So connect red to D2, white to Vcc, and black to GND.  For that screw terminal board, D2 will get connected to D7 if you plug the grove cable into the D6-7 socket on the Mayfly board.  We usually use the Mayfly’s D7 pin for SDI-12 sensors in all our sample code.

Shannon, I received 3 Meter CTD-10 (HYDROS 21) sensors this week and they did change the wire colors. For me brown is power (VCC) and orange is data (D2). I also had to use the b_address_change sketch to change the SDI-12 address from 0 to 1.

They did not give me a pinout, I just did trial and error of figure it out. I think next time I’ll purchase a stereo jack adaptor and try connecting it to the Mayfly that way.

Thanks for the info Brian.  I heard they were switching cable outer jacket colors soon, and a few of our workshop attendees last month received Hydros 21 sensors with black cable instead of the usual red, so I’m assuming the inner wire color changed too.  Their soil moisture sensors also changed inner wire colors a few years ago, and the manual shows both options.  It’s always good practice to double-check with a manufacturer if it’s unclear what wires to connect to a datalogger because some sensors can be damaged by connecting them to the wrong pins.  The Meter Group sensor seem to be pretty hearty and I haven’t accidentally broken one by connecting it wrong, but I’ve used other sensors that were immediately bricked by hooking it up wrong.

Shannon, yes, the outer jacket color I received is black. Good to know about the possibility of sensor damage or bricking.