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114 lines
4.0 KiB
114 lines
4.0 KiB
# Control a relay - Virtual IoT Hardware
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In this part of the lesson, you will add a relay to your Raspberry Pi in addition to the soil moisture sensor, and control it based off the soil moisture level.
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## Virtual Hardware
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The virtual IoT device will use a simulated Grove relay. This keeps this lab the same as using a Raspberry Pi with a physical Grove relay.
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In a physical IoT device, the relay would be a normally-open relay (meaning the output circuit is open, or disconnected when there is no signal sent to the relay). A relay like this can handle output circuits up to 250V and 10A.
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### Add the relay to CounterFit
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To use a virtual relay, you need to add it to the CounterFit app
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#### Task
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Add the relay to the CounterFit app.
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1. Open the `soil-moisture-sensor` project from the last lesson in VS Code if it's not already open. You will be adding to this project.
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1. Make sure the CounterFit web app is running
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1. Create a relay:
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1. In the *Create actuator* box in the *Actuators* pane, drop down the *Actuator type* box and select *Relay*.
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1. Set the *Pin* to *5*
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1. Select the **Add** button to create the relay on Pin 5
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The relay will be created and appear in the actuators list.
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## Program the relay
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The soil moisture sensor app can now be programmed to use the virtual relay.
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### Task
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Program the virtual device.
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1. Open the `soil-moisture-sensor` project from the last lesson in VS Code if it's not already open. You will be adding to this project.
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1. Add the following code to the `app.py` file below the existing imports:
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```python
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from counterfit_shims_grove.grove_relay import GroveRelay
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```
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This statement imports the `GroveRelay` from the Grove Python shim libraries to interact with the virtual Grove relay.
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1. Add the following code below the declaration of the `ADC` class to create a `GroveRelay` instance:
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```python
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relay = GroveRelay(5)
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```
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This creates a relay using pin **5**, the pin you connected the relay to.
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1. To test the relay is working, add the following to the `while True:` loop:
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```python
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relay.on()
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time.sleep(.5)
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relay.off()
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```
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The code turns the relay on, waits 0.5 seconds, then turns the relay off.
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1. Run the Python app. The relay will turn on and off every 10 seconds, with a half second delay between turning on and off. You will see the virtual relay in the CounterFit app close and open as the relay is turned on and off.
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## Control the relay from soil moisture
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Now that the relay is working, it can be controlled in response to soil moisture readings.
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### Task
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Control the relay.
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1. Delete the 3 lines of code that you added to test the relay. Replace them with the following code in its place:
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```python
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if soil_moisture > 450:
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print("Soil Moisture is too low, turning relay on.")
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relay.on()
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else:
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print("Soil Moisture is ok, turning relay off.")
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relay.off()
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```
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This code checks the soil moisture level from the soil moisture sensor. if it is above 450, it turns on the relay, turning it off if it goes below 450.
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> 💁 Remember the capacitive soil moisture sensor reads lower the more moisture there is in the soil.
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1. Run the Python app. You will see the relay turn on or off depending on the soil moisture levels. Change the *Value* or the *Random* settings for the soil moisture sensor to see the value change.
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```output
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Soil Moisture: 638
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Soil Moisture is too low, turning relay on.
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Soil Moisture: 452
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Soil Moisture is too low, turning relay on.
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Soil Moisture: 347
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Soil Moisture is ok, turning relay off.
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```
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> 💁 You can find this code in the [code-relay/virtual-device](code-relay/virtual-device) folder.
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😀 Your virtual soil moisture sensor controlling a relay program was a success!
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