15: Soil Moisture Sensor: Arduino and Particle Core
-- revised --
I programmed this first on an Arduino Nano. Pretty easy. My guesses at wiring did no damage. The "sunkee soil hygrometer" (probably meant "hydrometer") was mostly marked in Chinese. One tricky part: once you start the program the probe device is
on all the time -- drawing current. I first considered turning it on & off with a transistor. But then I wondered, why not just use a digital pin. I don't know if this is as safe, but it's simple and it works. In addition to short patch wires, I tested this using a 50' CAT5 cable between the probe and the interface. It worked fine. See post 27 at
http://dicks-raspberry-pi.blogspot.com/.
I had expected these things to be bigger.
Probe points only about 2" long.
Adjustment screw only useful for digital (ON/OFF) output.
Here's my Particle Core code. The Core can be read anywhere wifi is available (if you know the codes). So the Core can be remote from my Raspberry Pi control program.
/* device: "sunkee soil hygrometer" [SP?]
2 wires from probe "YL" & "69" (?) to interface board
no-label<->(YL) & GND<->(69?)
4 wires out to Arduino: "VCC" "GND" "D0" "A0"
Arduino or Particle/Core -- just guessing:
VCC -- 5v (or 3.3)
Arduino 5v: analog range=1023:200 (10 bits),
Core: analog range=4095:2000 (12 bits)
GND -- GND
D0 -- unused: just on/off
A0 -- analog pin
*/
int soil = A3; // read the device
int power = D1; // turn power on just for the reading
void setup() {
Spark.function("soil1", Soil); // Core-only function
pinMode(soil, INPUT);
pinMode(power, OUTPUT);
digitalWrite(power, LOW);
}
void loop() {
// not used
}
int Soil(String command) {
digitalWrite(power, HIGH); // turn probe on
delay(200); // let it settle?
int raw = analogRead(soil); // high=dry, low=wet
delay(200);
digitalWrite(power, LOW); // turn probe off
int read = map(raw,4095,2000, 0,20);
return read; // return reading between 0 & 20
}
