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Chapter two (lesson three)

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2-farm/lessons/3-automated-plant-watering/README.md
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@ -102,19 +102,19 @@ So far your relay is controlled by the IoT device directly based off a single so
1. Add the relevant MQTT libraries/pip packages and code to your `soil-moisture-sensor` project to connect to MQTT. Name the client ID as `soilmoisturesensor_client` prefixed by your ID. 1. Add the relevant MQTT libraries/pip packages and code to your `soil-moisture-sensor` project to connect to MQTT. Name the client ID as `soilmoisturesensor_client` prefixed by your ID.
> ⚠️ You can refer to [the instructions for for connecting to MQTT in project 1, lesson 4 if needed](../../../1-getting-started/lessons/4-connect-internet/README.md#connect-your-iot-device-to-mqtt). > ⚠️ You can refer to [the instructions for connecting to MQTT in project 1, lesson 4 if needed](../../../1-getting-started/lessons/4-connect-internet/README.md#connect-your-iot-device-to-mqtt).
1. Add the relevant device code to send telemetry with the soil moisture settings. For the telemetry message, name the property `soil_moisture`. 1. Add the relevant device code to send telemetry with the soil moisture settings. For the telemetry message, name the property `soil_moisture`.
> ⚠️ You can refer to [the instructions for for sending telemetry to MQTT in project 1, lesson 4 if needed](../../../1-getting-started/lessons/4-connect-internet/README.md#send-telemetry-from-your-iot-device). > ⚠️ You can refer to [the instructions for sending telemetry to MQTT in project 1, lesson 4 if needed](../../../1-getting-started/lessons/4-connect-internet/README.md#send-telemetry-from-your-iot-device).
1. Create some local server code to subscribe to telemetry and send a command to control the relay in a folder called `soil-moisture-sensor-server`. Name the property in the command message `relay_on`, and set the client ID as `soilmoisturesensor_server` prefixed by your ID. Keep the same structure as the server code you wrote for project 1, lesson 4 as you will be adding to this code later in this lesson. 1. Create some local server code to subscribe to telemetry and send a command to control the relay in a folder called `soil-moisture-sensor-server`. Name the property in the command message `relay_on`, and set the client ID as `soilmoisturesensor_server` prefixed by your ID. Keep the same structure as the server code you wrote for project 1, lesson 4 as you will be adding to this code later in this lesson.
> ⚠️ You can refer to [the instructions for for sending telemetry to MQTT](../../../1-getting-started/lessons/4-connect-internet/README.md#write-the-server-code) and [sending commands over MQTT](../../../1-getting-started/lessons/4-connect-internet/README.md#send-commands-to-the-mqtt-broker) in project 1, lesson 4 if needed. > ⚠️ You can refer to [the instructions for sending telemetry to MQTT](../../../1-getting-started/lessons/4-connect-internet/README.md#write-the-server-code) and [sending commands over MQTT](../../../1-getting-started/lessons/4-connect-internet/README.md#send-commands-to-the-mqtt-broker) in project 1, lesson 4 if needed.
1. Add the relevant device code to control the relay from received commands, using the `relay_on` property from the message. Send true for `relay_on` if the `soil_moisture` is greater than 450, otherwise send false, the same as the logic you added for the IoT device earlier. 1. Add the relevant device code to control the relay from received commands, using the `relay_on` property from the message. Send true for `relay_on` if the `soil_moisture` is greater than 450, otherwise send false, the same as the logic you added for the IoT device earlier.
> ⚠️ You can refer to [the instructions for for responding to commands from MQTT in project 1, lesson 4 if needed](../../../1-getting-started/lessons/4-connect-internet/README.md#handle-commands-on-the-iot-device). > ⚠️ You can refer to [the instructions for responding to commands from MQTT in project 1, lesson 4 if needed](../../../1-getting-started/lessons/4-connect-internet/README.md#handle-commands-on-the-iot-device).
> 💁 You can find this code in the [`code-mqtt`](./code-mqtt) folder. > 💁 You can find this code in the [`code-mqtt`](./code-mqtt) folder.
@ -122,7 +122,7 @@ Make sure the code is running on your device and local server, and test it out b
## Sensor and actuator timing ## Sensor and actuator timing
Back in lesson 3 you built a nightlight - an LED that turned on as soon as a low level of light was detected by a light sensor. The light sensor detected a change in light levels instantly, and the device was able to respond quickly, only limited by the length of the delay in the `loop` function or `while True:` loop. As an IoT developer, you can't always rely on such a fast feedback loop. Back in lesson 3 you built a nightlight - an LED that turns on as soon as a low level of light was detected by a light sensor. The light sensor detected a change in light levels instantly, and the device was able to respond quickly, only limited by the length of the delay in the `loop` function or `while True:` loop. As an IoT developer, you can't always rely on such a fast feedback loop.
### Timing for soil moisture ### Timing for soil moisture
@ -146,7 +146,7 @@ Imagine you have been tasked with building an irrigation system for a farm. Base
You could program the device in the same way as the nightlight - all the time the sensor reads above 450, turn on a relay to turn on a pump. The problem is that water takes a while to get from the pump, through the soil to the sensor. The sensor will stop the water when it detects a level of 450, but the water level will continue dropping as the pumped water keeps soaking through the soil. The end result is wasted water, and the risk of root damage. You could program the device in the same way as the nightlight - all the time the sensor reads above 450, turn on a relay to turn on a pump. The problem is that water takes a while to get from the pump, through the soil to the sensor. The sensor will stop the water when it detects a level of 450, but the water level will continue dropping as the pumped water keeps soaking through the soil. The end result is wasted water, and the risk of root damage.
✅ Remember - too mch water can be as bad for plants as too little, and wastes a precious resource. ✅ Remember - too much water can be as bad for plants as too little, and wastes a precious resource.
The better solution is to understand that there is a delay between the actuator turning on and the property that the sensor reads changing. This means not only should the sensor wait for a while before measuring the value again, but the actuator needs to turn off for a while before the next sensor measurement is taken. The better solution is to understand that there is a delay between the actuator turning on and the property that the sensor reads changing. This means not only should the sensor wait for a while before measuring the value again, but the actuator needs to turn off for a while before the next sensor measurement is taken.
@ -156,7 +156,7 @@ How long should the relay be on each time? It's better to err on the side of cau
![A strawberry plant connected to water via a pump, with the pump connected to a relay. The relay and a soil moisture sensor in the plant are both connected to a Raspberry Pi](../../../images/strawberry-with-pump.png) ![A strawberry plant connected to water via a pump, with the pump connected to a relay. The relay and a soil moisture sensor in the plant are both connected to a Raspberry Pi](../../../images/strawberry-with-pump.png)
For example, I have a strawberry plant with a soil moisture sensor and a pump controlled by a relay.I've observed that when I add water it takes about 20 seconds for the soil moisture reading to stabilize. This means I need to turn the relay off and wait 20 seconds before checking the moisture levels. I'd rather have too little water than too much - I can always turn the pump on again, but I can't take water out of the plant. For example, I have a strawberry plant with a soil moisture sensor and a pump controlled by a relay. I've observed that when I add water it takes about 20 seconds for the soil moisture reading to stabilize. This means I need to turn the relay off and wait 20 seconds before checking the moisture levels. I'd rather have too little water than too much - I can always turn the pump on again, but I can't take water out of the plant.
![Step 1, take measurement. Step 2, add water. Step 3, wait for water to soak through the soil. Step 4, retake measurement](../../../images/soil-moisture-delay.png) ![Step 1, take measurement. Step 2, add water. Step 3, wait for water to soak through the soil. Step 4, retake measurement](../../../images/soil-moisture-delay.png)
@ -181,7 +181,7 @@ The server code can be modified to add control around the timing of the watering
1. Telemetry message received 1. Telemetry message received
1. Check the soil moisture level 1. Check the soil moisture level
1. if it's ok, do nothing. If the reading is too high (meaning the soil moisture is too low) then: 1. If it's ok, do nothing. If the reading is too high (meaning the soil moisture is too low) then:
1. Send a command to turn the relay on 1. Send a command to turn the relay on
1. Wait for 5 seconds 1. Wait for 5 seconds
1. Send a command to turn the relay off 1. Send a command to turn the relay off
@ -206,6 +206,13 @@ Update your server code to run the relay for 5 seconds, then wait 20 seconds.
1. Open the `app.py` file 1. Open the `app.py` file
1. Add the following code to the `app.py` file below the existing imports:
```python
import threading
```
This statement imports `threading` from Python libraries, threading allows python to execute other code while waiting.
1. Add the following code before the `handle_telemetry` function that handles telemetry messages received by the server code: 1. Add the following code before the `handle_telemetry` function that handles telemetry messages received by the server code:
```python ```python
@ -272,6 +279,8 @@ Update your server code to run the relay for 5 seconds, then wait 20 seconds.
A good way to test this in a simulated irrigation system is to use dry soil, then pour water in manually whilst the relay is on, stopping pouring when the relay turns off. A good way to test this in a simulated irrigation system is to use dry soil, then pour water in manually whilst the relay is on, stopping pouring when the relay turns off.
> 💁 You can find this code in the [`code-timing`](./code-timing) folder.
> 💁 If you want to use a pump to build a real irrigation system, then you can use a [6V water pump](https://www.seeedstudio.com/6V-Mini-Water-Pump-p-1945.html) with a [USB terminal power supply](https://www.adafruit.com/product/3628). Make sure the power to or from the pump is connected via the relay. > 💁 If you want to use a pump to build a real irrigation system, then you can use a [6V water pump](https://www.seeedstudio.com/6V-Mini-Water-Pump-p-1945.html) with a [USB terminal power supply](https://www.adafruit.com/product/3628). Make sure the power to or from the pump is connected via the relay.
--- ---

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2-farm/lessons/3-automated-plant-watering/assignment.md
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@ -6,7 +6,7 @@ This lesson covered how to control a relay via sensor data, and that relay could
For this assignment you will calculate how long the pump should run for a particular rise in soil moisture. For this assignment you will calculate how long the pump should run for a particular rise in soil moisture.
> ⚠️ If you are using virtual IoT hardware, you can work through this process, but simulate the results by increasing the soil moisture reading manually by a fixed amount per second the relay us on. > ⚠️ If you are using virtual IoT hardware, you can work through this process, but simulate the results by increasing the soil moisture reading manually by a fixed amount per second the relay is on.
1. Start with dry soil. Measure the soil moisture. 1. Start with dry soil. Measure the soil moisture.
@ -37,4 +37,4 @@ For this assignment you will calculate how long the pump should run for a partic
| Criteria | Exemplary | Adequate | Needs Improvement | | Criteria | Exemplary | Adequate | Needs Improvement |
| -------- | --------- | -------- | ----------------- | | -------- | --------- | -------- | ----------------- |
| Capture soil moisture date | Is able to capture multiple readings after adding fixed quantities of water | Is able to capture some readings with fixed quantities of water | Can only capture one or two readings, or is unable to use fixed quantities of water | | Capture soil moisture date | Is able to capture multiple readings after adding fixed quantities of water | Is able to capture some readings with fixed quantities of water | Can only capture one or two readings, or is unable to use fixed quantities of water |
| Calibrate the server code | Is able to calculate an average decrease in soil moisture reading and update the serve code to use this | Is able to calculate an average decrease, but cannot update the server code, or is unable to correctly calculate an average, but uses this value to correctly update the server code | Is unable to calculate an average, or update the server code | | Calibrate the server code | Is able to calculate an average decrease in soil moisture reading and update the server code to use this | Is able to calculate an average decrease, but cannot update the server code, or is unable to correctly calculate an average, but uses this value to correctly update the server code | Is unable to calculate an average, or update the server code |

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2-farm/lessons/3-automated-plant-watering/pi-relay.md
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@ -78,7 +78,7 @@ Now that the relay is working, it can be controlled in response to soil moisture
Control the relay. Control the relay.
1. Delete the 3 lines of code that you added to test the relay. Replace them with the following code in its place: 1. Delete the 3 lines of code that you added to test the relay. Replace them with the following code:
```python ```python
if soil_moisture > 450: if soil_moisture > 450:
@ -89,11 +89,11 @@ Control the relay.
relay.off() relay.off()
``` ```
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. This code checks the soil moisture level from the soil moisture sensor. If it is above 450, it turns on the relay, and turns it off when it goes below 450.
> 💁 Remember the capacitive soil moisture sensor reads lower the more moisture there is in the soil. > 💁 Remember the capacitive soil moisture sensor reads the lower the soil moisture level, the more moisture there is in the soil and vice versa.
1. Run the Python app. You will see the relay turn on or off depending on the soil moisture levels. Try in dry soil, then add water. 1. Run the Python app. You will see the relay turn on or off depending on the soil moisture level. Try in dry soil, then add water.
```output ```output
Soil Moisture: 638 Soil Moisture: 638

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2-farm/lessons/3-automated-plant-watering/virtual-device-relay.md
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@ -1,6 +1,6 @@
# Control a relay - Virtual IoT Hardware # Control a relay - Virtual IoT Hardware
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. In this part of the lesson, you will add a relay to your virtual IoT device in addition to the soil moisture sensor, and control it based off the soil moisture level.
## Virtual Hardware ## Virtual Hardware
@ -93,9 +93,9 @@ Control the relay.
relay.off() relay.off()
``` ```
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. 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.
> 💁 Remember the capacitive soil moisture sensor reads lower the more moisture there is in the soil. > 💁 Remember the capacitive soil moisture sensor reads the lower the soil moisture level, the more moisture there is in the soil and vice versa.
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. 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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2-farm/lessons/3-automated-plant-watering/wio-terminal-relay.md
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@ -70,7 +70,7 @@ Now that the relay is working, it can be controlled in response to soil moisture
Control the relay. Control the relay.
1. Delete the 3 lines of code that you added to test the relay. Replace them with the following code in its place: 1. Delete the 3 lines of code that you added to test the relay. Replace them with the following code:
```cpp ```cpp
if (soil_moisture > 450) if (soil_moisture > 450)
@ -85,13 +85,13 @@ Control the relay.
} }
``` ```
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. This code checks the soil moisture level from the soil moisture sensor. If it is above 450, it turns on the relay, and turns it off when it goes below 450.
> 💁 Remember the capacitive soil moisture sensor reads lower the more moisture there is in the soil. > 💁 Remember the capacitive soil moisture sensor reads the lower the soil moisture level, the more moisture there is in the soil and vice versa.
1. Build and upload the code to the Wio Terminal. 1. Build and upload the code to the Wio Terminal.
1. Monitor the device via the serial monitor. You will see the relay turn on or off depending on the soil moisture levels. Try in dry soil, then add water. 1. Monitor the device via the serial monitor. You will see the relay turn on or off depending on the soil moisture level. Try in dry soil, then add water.
```output ```output
Soil Moisture: 638 Soil Moisture: 638

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