Help needed for soil moisture sensing...

karthi27 · Joined: 18 Nov 2009 Posts: 10

I need to design a cheap soil moisture sensor using PIC 16f877.
I referred http://www.faludi.com/2006/11/02/moisture-sensor-circuit/
I simulated it in multisim. It didn't yield satisfactory results.

All that i need is to send an analog signal to the controller based on the soil resistance. I need the hardware circuitry.
I shall take care of the programming.
_________________
Regards
Karthi

SherpaDoug · Joined: 07 Sep 2003 Posts: 1640 Location: Cape Cod Mass USA

I really don't like that circuit. Unless someone can explain how it works to me I would start with the basic ohmmeter circuit in the Microchip application note AN512. It is written in assembler, but if you understand it you can write it in C easily enough.
_________________
The search for better is endless. Instead simply find very good and get the job done.

Guest · Posted: Tue Dec 15, 2009 9:21 am

Another problem, actually for all DC powered soil sensors, is the bias that accumulates over time due to the sensor current flow. This can be eliminated by using an AC source to the sensor, then converting the signal to dc for the PIC. Another option is to control the power to the sensor and only power it when a reading is desired.
Jay