Science Buddies: "Ask an Expert"

When trying to calibrate the soil moisture sensor, step 3 says the serial monitor in Arduino should read 0 when the probes aren't touching anything. We get a reading of 13 and 14. It also changes very little when we touch the probes with a finger. Can you please advise as to why we aren't getting a reading of 0?


[Administrator note: Project: https://www.sciencebuddies.org/science- ... t-watering ]

So that Experts can best help you troubleshoot, can you please upload a photo of your circuit (as clear as possible) so that it can be reviewed.

You mention the readings are off. Is the red LED on when the probes are not touching anything?

"The serial monitor should read 0 and the red LED should be on when the probes are not touching anything."

Amy
Science Buddies

His red light did turn on when not touching anything. We went ahead with the steps of calibration to see what we could get and the lowest it went was 12 as the dry reading.

He also went ahead with the programming of the pump. At first it seemed to be working. The blue light was on and the soil wet. However once the pump turned on it wouldnt ever shut off ans over watered the plant. The yellow light wouldnt ever turn on either. We set up the layout we had in the simulation and it seemed OK, so I'm not sure what to do now.

The one picture is with the soul sensor out since it got flooded with the over watering and we wanted to let it dry.

Hi - can you clarify what exactl you mean by "went ahead with the steps of the calibration" and "went ahead with the programming of the pump"?

1. What did you change the "wet" and "dry" variables to in your code?
2. When you run the program and open the serial monitor, what is it printing out for the sensor value, when the soil is initially dry, and after the pump has filled it with water?

Look at the if/else statement in the code - if the "sensor" value stays below the "dry" value, then the pump will always be on. Even if it was working in the simulation, what matters here is the real-world values with the actual sensor.

That is all assuming the MOSFET is wired correctly. It's possible to wire the MOSFET wrong, such that the pump will just always be on, regardless of what the code is doing. It *looks* like it's wired correctly in your pictures, but it's hard for me to tell for sure - if you can upload more pictures just of the breadboard (not zoomed out of the entire setup), I can double check.