The pot plant monitor
This pot plant is connected to my computer. Every five minutes or so, the resistance of the soil is measured. The resistance varies indirectly with the dampness of the soil, as you can see in the graph.
I water the plant every few days, as indicated. It would be fun to extend this into a full-blown irrigation system by building some kind of motorized watering contraption, but I don't want to risk the wooden floor. =)
How the sensor works
This is the world's cheapest ohm-meter:
The microcontroller drains the capacitor by providing a 0V output on the pin. It then re-configures the pin into a high-impedance input pin and resets an internal clock. Now the capacitor is slowly charged through the resistor (soil), and when the voltage level has become so high that it corresponds to a logical 1, the microcontroller receives a pin change interrupt, reads the clock and reports this value to the computer.
Posted Wednesday 9-Jan-2008 18:20
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Mon 31-Mar-2008 16:43
Current flows. Electrolysis will happen. The electrodes will dissolve over time. There's a magnetic field, etc.
Thu 3-Apr-2008 11:40
Wed 9-Apr-2008 17:47
Wed 9-Apr-2008 17:56
Electrolysis would happen to a very small extent, but it can be minimized in the same way as the current.
Time to put that gold jewelry to use! It won't dissolve if used as electrodes.
The magnetic field would probably not be strong enough to be measurable with affordable instruments, given the small current.
Thu 10-Apr-2008 13:42
-webpresence04 at soulsurf se
Thu 10-Apr-2008 22:25
Good point. I'm using a 10 uF electrolytic capacitor.
Mon 14-Apr-2008 23:35
Tue 22-Jul-2008 13:51
Don't even need to do that, as the capacitor will charge up until there is close to zero volts across the resistor (in this case, the soil).
Sat 9-Aug-2008 11:49
Sun 17-Aug-2008 23:33
I have got two suggestions on how to improve it a little bit:
1. There is no need for a high frequency of measurements and therefore also no need to always provide +5 V. Just connect this path to another uC pin and while no measurement is in progress, let both uC pins provide GND level.
2. Put a resistor (suggestion: 220 Ohms) in serial with the measuring uC pin to protect the uC. Although the capacitance of the capacitor is not too high, a large amount of current will flow in a very short period of time while it is discharged.
Fri 23-Jul-2010 22:17
I've always thought the same thing. I've been dreaming about an automated greenhouse. I have all the control side down, but the moisture sensing circuitry was a little bit of a problem for me.
Thanks to you, I have that almost all figured out. The next step is to blend the sensing and controls together.
The problem I'm having is to get an output signal send to the controller once a setpoint is reached.
p.s. you can really mislead someone with the title "pot plant" hehe
Mon 7-May-2012 15:49
once you know the 'ideal' weight for the moist level that the plant needs.
to dry then switch on a little airpump (aquarium pump) that pushes the water out of a closed jar, or a stepper motor pump (like in the old xerox inkjets) that pushes the fluid trough a medical rubber tube.
Tue 5-Jun-2012 07:07
Sun 13-Oct-2013 08:37
How do you account for the plants growth?