You will need some basic experience with soldering, breadboarding and using the Arduino platform for this tutorial.
This particular instructable is for a sensor that will upload it's data via an Ethernet connection. Your plant will preferably be indoors. It's a bit cheaper and easier than the WIFI version, but if you're feeling adventurous, you can check out the WIFI version here.
To build a plant sensor, you will need the following:
] 1 x Arduino Ethernet
] 1 x FTDI > USB cable
] 1 x Ethernet Cable (Cat 5E patch)
] 1 x DHT22 Temperature + Humidity sensor
] 1 x LDR (Light dependent resistor)
] 2 x 10Kohm resistors
] 2 x Nails (Any nails will do for now, galvanized is best though)
] Plenty of hook up wire (single core wire)
] A Soldering iron & plenty of solder
] A Mac or windows computer
We have provided links to some of the trickier parts to find.
Once you think you have everything, you can continue to the next step to get started!
Step 1: Connect up the DHT22
Here's a few specs:
- 3 to 5V tolerant
- Good for 0-100% humidity readings with 2-5% accuracy
- Good for -40 to 125°C temperature readings ±0.5°C accuracy
- No more than 0.5 Hz sampling rate (once every 2 seconds)
- Body size 15.1mm x 25mm x 7.7mm
There are four pins but only three are used as follows:
So we just need to connect the Arduino 5V to pin 1, Arduino digital pin5 to pin 2 and GND to pin 3. Check the picture for the pin numbers.
As far a reading the data goes, there is a library included with the files in this intractable that will sort that out for you.
Step 2: Connect up the LDR
Hook it up as in the digram below.
Step 3: Connect up the moisture sensor
Unfortunately if we just stick two wires into the soil and pass a DC current through it, we will be performing electrolysis, which causes the water molecules in contact with the wires to breakdown, releasing oxygen and hydrogen. Not only does this cause little bubbles to appear over the wire's surface thus reducing it's ability to pass current, but it will also rapidly erode the wires.
The 'solution' (I use inverted commas since it doesn't solve the problem as much as to slow it..) is to alternate the current. This means you send the current through the wires one way then the other way, in theory preventing electrolysis. In practice, it doesn't work forever, so we may have to change the soil contacts every couple of months, but that's a small price to pay for the simplicity of this method of moisture measurement.
Below is the circuit we use to connect it up.
The code to alternate the current and take a reading is all in the Arduino sketch later in this instructable.
Step 4: Create a Cosm feed
You will need to set up a 'feed', which will hold all the sensor data for your plant.
Head over to http://cosm.com set up an account. The website will guide you through this process.
Create a new feed and make a note of your api key, feed number and project title.
We can then put these in your arduino sketch so that the data ends up in the right place.
Step 5: Program Arduino
Attached below is a zip file with the following folder:
DHT22 - Library to get data from the DHT22 sensor.
stats_ethernet - The stats in sound arduino sketch
First, add the DHT22 library to Arduino (if unsure how check here). Next, move the stats_ethernet folder to your Arduino folder and open up the sketch inside. Towards the top of the sketch there are the settings for your API key, feed ID and project title. All you need to do is fill those in, upload the sketch and it should start working. If you are having difficulties, you can try modifying the static IP address and MAC address in the code, as mentioned in the code comments.
You should now be able to see the uploaded data on your Cosm page.
Step 6: Listen to the music!
Type your feed ID into the box and select the type of composition you would like to hear. Remember you will need a week's worth of data in your Cosm feed before you can use the 'Past week' or 'Past day' functions.
Enjoy and please let us know how it goes.