SDI-12 Change Address for Meter Hydros 21 CTD Sensor

It sounds like your PC is just not seeing the Mayfly. You should make sure the Mayfly is turned on at the main power switch, and that the small power-select slide switch is set to the USB/Lipo setting (not Ext). Sometimes the switches can be a little glitchy, so you can try sliding them back and forth to make sure they’re getting good contact. And also ensure that you’re using a proper microUSB cable, like the one that came with the starter kit, if you bought one. Some users have reported issues with cheaper cables due to bad connections, broken wires, or bent pins on the cable. And verify that you’ve chosen the proper COM port in the Arduino IDE settings. Sometimes your computer will assign a new COM port to the Mayfly, but the IDE doesn’t always update the COM setting to the newest port, so it’s looking for the Mayfly on the wrong port.

What you’re describing with the microSD card is definitely not normal. I’ve encountered it only a few other times in over 1000 boards, and it’s usually caused by a bent pin inside the microSD socket that causes a short circuit when a card is inserted. Is this a brand new board? And are you seeing this behavior with the microSD socket that’s built into the Mayfly, or with the supplemental vertical microSD card adapter board (that comes with the starter kit) that plugs into the 8-pin SPI header between the power switch and the D21 pushbutton? And do you see this same behavior with various microSD cards, or just one? Sometimes a malfunctioning microSD card will cause the problem instead of the socket itself.

The Mayfly is not designed to have 2 microSD cards inserted at the same time. No one should ever insert two cards. The reason for the second vertical socket is for people who have the logger mounted inside an enclosure that makes it difficult to remove the card in the regular horizontal socket. Various electrical irregularities will occur if you use two cards at the same time, and the processor will only write to one card anyway, so there’s no benefit to having two cards in together.

So are you saying that the board performs properly as long as you’re using only one card? Because I have seen a few of the optional vertical memory card adapter boards have the bent pin that results in the short circuit when a single card is inserted. The issue is fixed by simply replacing the vertical memory card board. I’ve never seen a Mayfly have the issue with the onboard horizontal memory card socket because that’s one of the things I test for before shipping each Mayfly.

The Mayfly logger processor is just like any other Arduino board, and loading sketches onto it is just like any other Arduino board. The uploaded sketch is “burned” into the microprocessor chip in the center of the board. The microSD card slot is just an optional device to allow users to store recorded variables or other data during the subsequent operation of the logger. The Mayfly is not like a Raspberry Pi that has an actual operating system and executable files on the memory card.

Regarding SDI-12 addressing, you can connect a Hydros 21 sensor to any pins you want, you just need one data line, one power excitation line, and one ground line. Are you using a sensor with bare wires or did you purchase one with the 3-pin stereo plug (3.5mm)? If you’re using the stereoplug-to-grove adapter board that we sell, then just use a grove cable to connect the adapter board to the Mayfly’s D6-D7 grove jack, and then you would use data pin 7 in the sketch. If you’re using a bare wire sensor, then you’re free to connect them to any free digital pin, but for simplicity you should use D7 when starting out so you don’t have to change the sketch. The reason for the power excitation pin D22 in the sketch is that the onboard switchable voltage regulator is controlled by turning on pin D22. But you need to hook any external sensors you want to operate to the “Switched 3v” line because that’s where the actual switched power comes from, and not D22. Again, this is taken care of if you’re using the grove jack stereo plug adapter board, but you have to hook it up right if you’re using a bare wire sensor. Whenever D22 is on, there’s a red LED in the bottom corner of the Mayfly that comes on to indicate that the sensor (and anything else on the switched 3v or switched 5v line) is being powered.