98 lines
3.0 KiB
Markdown
98 lines
3.0 KiB
Markdown
# Code
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You will need to get a pot of dry dirt and wet dirt for the coding.
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## Step 1: Measuring moisture
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The soil acts as a variable resistor based on the amount of water and nutrient.
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The water is not conductive but the nutrient are, so more water, more nutrient, so the soil will be less resistive.
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To measure this, we read the voltage on pin ``P0`` using [analog read pin](/reference/pins/analog-read-pin)
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which returns a value between ``0`` (no current) and ``1023`` (max current). The value is graph on the screen
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using [led plot bar graph](/reference/led/plot-bar-graph).
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```blocks
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basic.forever(() => {
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led.plotBarGraph(
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pins.analogReadPin(AnalogPin.P0),
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1023
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)
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})
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```
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## Experiment!
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* insert the nails in the dry dirt and you should see most LEDs off
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* insert the nail in the wet dirt and you should see most LEDs on
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## Step 2: Sensor data values
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In the previous program, we only have a rough idea of the value of the sensor... since it is using a tiny screen
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to display it! Let's add code that displays the current reading when button ``A`` is pressed.
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This code has to be inserted in the forever loop. We've also added a variable ``reading`` to store the reading value.
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```blocks
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let reading = 0
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basic.forever(() => {
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reading = pins.analogReadPin(AnalogPin.P0)
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led.plotBarGraph(
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reading,
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1023
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)
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if (input.buttonIsPressed(Button.A)) {
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basic.showNumber(reading)
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}
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})
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```
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## Experiment!
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* insert the nails in the dry dirt, press ``A`` and note the value. You should see a value close to ``250``
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for dry dirt.
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* insert the nails in the wet dirt, press ``A`` and note the value. You should see a value close to ``1000``
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for wet dirt.
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https://youtu.be/S8NppVT_paw
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## Step 3: Don't waste energy!
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We want our probe to work for a long time on batteries so we need to tweak our code to save energy.
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* Our circuit connects directly to the ``3v`` pin so it is always using electricity. Instead,
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we will connect it to ``P1`` and turn that pin high only while the measurement is taken.
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This saves electricty and also avoids corrosion of the probes.
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* We will also lower the brightness of the screen to lower the energy consumption from the LEDs.
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* Soil moisture changes very slowly so we don't need to measure all the times!!! Let's add a **sleep** of 5 seconds in the loop as well.
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```blocks
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led.setBrightness(64)
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let reading = 0
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basic.forever(() => {
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pins.analogWritePin(AnalogPin.P1, 1023)
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reading = pins.analogReadPin(AnalogPin.P0)
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pins.analogWritePin(AnalogPin.P1, 0)
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led.plotBarGraph(
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reading,
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1023
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)
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if (input.buttonIsPressed(Button.A)) {
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basic.showNumber(reading)
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}
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basic.pause(5000);
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})
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```
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## Experiment!
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* using the dry and wet dirt pots, test that your ciruit still works. Remember you'll have to wait up to 10 seconds to see a change!
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## ~button /projects/soil-moisture/connect
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Connect
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## ~ |