Hello everyone. This is such a helpful community. I got in over my head. I'm hoping I have come to the right place.
I have been struggling with an analog sensor circuit I designed and am growing tired of ordering parts just to find out that I need something else.
I am using an Arduino Mega with a wing protoshield (screw terminals) and a w5100 ethernet shield. The sensors I am hooking up are the VH400 from Vegetronix. It reads soil moisture and outputs a 0-3V signal. When I had only one sensor hooked up everything seemed fine. Now that I have 14 fully wired it appears the signal is unreliable, skewing towards too high a voltage.
I do not have a diagram but I can try to sketch one up if needed. I will do my best to describe the wiring: A 12v 1A wall wart (switching I believe but I can check) powers a bus. All fourteen sensors connect via that bus. The sensors are 13mA I believe. The Arduino is also wired to the bus via the dc input jack. Each sensor is then connected to the analog sensors on the arduino. Wiring used is shielded, with the dc neutral running on a conductor as well as the shield. (I should stop to mention here that during testing I did not believe this sensor would work in a high RF environment but it worked fine with this wiring. It is now in a lower rf environment.) All wires are connected with insulated quick disconnect terminals. The power bus and the arduino are wired in a metal electrical box, which is also tied to the dc neutral, although removing that bond didn't seem to affect anything.
Right now I believe I just need an op amp for each sensor. Which means rewiring everything. I also ordered an op amp, not realizing I was ordering something much smaller than I am capable of soldering or using on a breadboard.
I have linked a wiring diagram from Vegetronix that shows how to wire this into a larger sprinkler system. What is not clear to me is if I only need the op amp or if I need all the parts. I am just looking to be done with this project as it has gone on far too long.
Thanks for any help.