Fab Academy 9

Input Devices

Soil Moisture Sensor


For this project I first tried to program a Soil Moisture Sensor (the one with two sticks) I bought to check the moisture of my plants soil by capacitive conductivity, which means that the amount of water between the two sticks generates certain conducticity which can be measured and then turned into an action.

The kit also comes with another water humidity sensor, that measures the amount of rain or reacts to when the rain falls. You can also use this one to measure the amount of wather inside a bowl, since it also reacts to conductivity, so the more water it has around, the more conductivity it has and therefore, more signal it sends. I dind´t used this one in my experiments anyway.

This is the tutorial I started from.

ESP8266 12-E Chip Pinout

Serial Read:

The first thing I did was to do a serial read to understand the values that it was giving me.

That showed me that the values ocillated from 0 to 430 more or less. 0 when it had no current between the two sticks (no conductivity), 400-430 when it was inside water or fully moistured soil, but there was another value when the soil was almost dry (similar to fingers conductivity) which was between 50 and 100.


ESP8266 12-E Chip Pinout

Building the Code

Since the values were around 400, I diveded them by 4, to turn them into an average percentage, for the Serial.printIn.

I wanted to check 3 values (Dry, Almost Dry, Wet), so I added 3 different color leds to my system (Red, Yellow, Green) with 220 ohms resistors.

I started tweaking the threshold code to set it up, so that each led lighted up when it was between a different threshold value.

I declared the main threshold to be 100, and decided that:

If the DATA was >= than (THRESHOLD + 200), the GREEN LED turns ON.

If the DATA was <= than THRESHOLD, the RED Led turns ON.

If the DATA was > than THRESHOLD and < than the (THRESHOLD + 200), the YELLOW LED turn ON.

And I added a delay to loop this process each 500 milliseconds.



I was having some troubles at he begining because I didn´t know how to have two conditions togheter like in the case of the YELLOW LED, so in some moment two leds where turning on at the same time, but I solved it with an AND code:

        else if (data >= (threshold) and (data < threshold + 200)) 

I was also having troubles with diferenciating the conditions of the three leds, because I was only usinf IF code, but I solved it by adding somo ELSE IF.

PCB Board Connection

(BOM) Bill Of Materials

Home Made
Moisture Sensor


After trying with a comercial soil sensor, I wanted to try the tutorial for creating my own soil sensor. In this one I basically followed the instructions to build it, and then copied the code.

For this sensor, different to the one I previously did, the main difference is that they create the sensor with two bolts attached to wires. This works practicaly the same as commercial ones, bi generating a signal based on the conductivity between the two bolts generated by the water that moistures the soil.

Another difference is that they use a RGB 4 LEGS LED, instead of 3 different color Leds that I was using.

One thing to keep in mind is that since you are not using an average distance between the two bolts, maybe is a good idea to add them something so that the distance is always the same.

To solve that, I used a piece of cardboard and some tape, to create some structure for the bolts and wires, and it looks pretty nice and less sturdy, and it will also help you to have an equal measure condition every time, since the distance between the bolts maintains the same.

ESP8266 12-E Chip Pinout

BOM (Bill Of Materials)

3 x 220 ohm Resistors
1 x 10K ohm Resistor
1 x RGB Diffused Common Anode LED
2 Bolts
8 x Male/male jumper wires
1 x Breadboard
1 x Arduino UNO (in this case)

Sensor Optimization (optional)

ESP8266 12-E Chip Pinout

The Original Code:

The tutorial code differs from the one I used before, because:

- The type of led they use.
- How the translation of data into a percentage is averaged .
- The way they declare the ELSE IF and IF values.
- The way they set the values for TOO WET and TOO     DRY.

My main learning from this code was that they declare two thresholds for TOO WET and TOO DRY, and for each led color they use s simplier function for them by just using <= or >= than thresholds. In that way they are able to leave the third LED option without any condition, so it will light with every data inbetween this two assigned conditions.

I really didn´t understood the code percentage operation, and I don´t know where these numbers they multiply and sum come from, so I changed the code 

    int percent = 2.718282 * 2.718282 * (.008985 *     moistVal + 0.207762);



My Modified Code:

1) Read sensor totally dry (it should be 0)

2) Read sensor inside a water glass. (that should give you the highest reading)

3) Divide highest sensor read number by 100. (In my case it was 870/100 = 8.7)

4) Divide Sensor read in the code by the number you got to have a percentage:

    moistVal = analogRead(moistPin);
    int percent = moistVal/8.7;
    Serial.println("% Moisture ");

5) I also used the 8.7 I´ve got before, to declare what was to wet or too dry for me, and then multiply it by the percentage I wanted. In my case it is Too Dry if it is below 30% or Too Wet if it is above 70%:

    int tooDry = 8.7*30;
    int tooWet = 8.7*70;

6) I Also added a fancy Serial.printIn after each read, so that it tells you if it´s too dry, too wet, or good moisture.



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