Hydra Probe Connections

Stevens Hydra Probe Connections to the BoSL Board - SDI-12 Version

This page describes the set up of the Hydra Probe with the BoSL board. The hydra probe details can be found here: https://www.stevenswater.com/resources/documentation/hydraprobe/HydraProbe_Manual_Jan_2018.pdf

Some details about the probe:

• it is SDI-12 and presumably the line is around 5v but often this has worked with our boards so i am not too concerned about that.
• the probe should work between 9 and 16v, which is a lot higher than our board requires. we either need an alternate power supply (and a step down to the logger too) or a step up regulator.
• the probe has ZERO information about which pins are which, so I needed to use a multimeter to find out which pins are likely right. It was clear which was the GND and SIGNAL as it had a measurable and likely the lowest resistance, where as the other combinations had no resistance. As such, I knew which was the +ve 12v and which was not. My first attempt of which was GND and SIGNAL was wrong, so i swapped and voila.

Some details about the logger and programs:

• SDI-12 logger already exists for Arduino IDE.
• our BoSL 0.5.x boards run at 8MHz which seems to cause some issues with the SDI-12 package. In comes Stephenio to the rescue and has posted this online: : https://github.com/StephenCatsamas/Arduino-SDI-12/archive/refs/heads/master.zip. then in the arduino IDE go Sketch -> Libraries -> add .ZIP library.
• so until now i have not tested it on our boards and instead have used a nano. Just use the standard SDI-12 package (G-Terminal), uploaded it to nano, connected signal to D4, GND of sensor to GND of nano, power of sensor to 12v supply, powered the nano via computer, then check Page 46 of https://www.stevenswater.com/resources/documentation/hydraprobe/HydraProbe_Manual_Jan_2018.pdf and you will see that first you initiate the measurement using command aM! (a is the address in this case 0) then it will respond with the 00029 which means 2 seconds delay and 9 characters will be returned. Then wait 2 seconds and then type aD0!, aD1!,aD2! and you will get lots of info.

Video

https://www.youtube.com/shorts/DucZr9Bw8uE

Summary of setup

Overview This video documents testing an SDI-12 sensor with an Arduino Nano, including troubleshooting voltage requirements and connection setup. Key Findings Voltage Requirements:

Sensor requires at least 9 volts to function properly Lower voltages (below 9V) produce unreliable/bogus readings Higher voltages were also tested but 9V appears optimal

Hardware Compatibility Issues:

Initial attempt with "Bossle board" failed Error related to incorrect clock frequency Issue reported to Stinio (manufacturer/support)

Successful Setup Configuration Wiring Connections:

Black wire → Ground (connected to Arduino Nano ground) White wire → Signal (connected to digital pin 4 on Nano) Red wire → +9V power supply Ground → Shared between sensor and Arduino Nano

Software Setup:

Used Arduino SDI-12 library (generic terminal example) Modified pin assignment to digital pin 4 Removed power pin configuration (externally powered) Set sensor address to 0

Results

Temperature reading: 23.9°C (accurate for room temperature) Additional measurements: Two other values that respond to physical contact with sensor prongs (likely moisture/conductivity related) Communication protocol: SDI-12 with 2-second measurement time and 9-digit response

Technical Notes

Sensor has 3-pin connection No clearly visible distinguishing markings on sensor exterior Successfully communicates using standard SDI-12 protocol commands (M1 for measurement request)

This setup provides a working foundation for integrating the sensor into larger monitoring systems.

Update - next day from above - 20th August 2025

https://www.youtube.com/shorts/_PXq_4ljlek
In this second night of the HydraProbe testing, significant progress was made using the BoSL board with Steven's updated code. The operating voltage was successfully reduced from the manufacturer's recommended range of 9-16V down to just 7.2V, with 7V proving sufficient for reliable operation. While initial connectivity issues occurred with digital pin 4 on the BoSL Board , switching to pin A11 resolved the problem completely. The testing setup is now working well with a simple code (direct from the fiel that Stephen provided above - d_simple_logger - configuration using a 9600 baud serial connection and data pin A11. When testing the sensor in water, consistent temperature readings around 22°C are being achieved. The testing revealed that maintaining voltage above 7V is crucial, as dropping below this threshold causes temperature readings to become unreliable (showing incorrect values around 5°C), though other parameters remain stable even at these lower voltages. Overall, the system is producing consistent and reliable readings over time, representing solid progress on the project.