Created October 16, 2022

Plant health monitoring system

various measurements are taken on plants to measure and subsequently evaluate the health status of the plants.

Runner Ups

Smarter Sustainable World Challenge

Things used in this project

Hardware components

Nordic Semiconductor Nordic Thingy:53

Seeed Studio Grove - Capacitive Soil Moisture Sensor

or any other capacitive soil moisture sensor

Nordic Semiconductor nRF51822 Bluetooth Low Energy and 2.4 GHz SoC

Preferably on a certified module

Adafruit HUZZAH32 – ESP32 Feather Board

or any other ESP32 development board, which supports BLE and WiFi

Story

Most of the time it is enough to measure the soil moisture on a plant to determine the health status of a plant. However, this can only be a statement about whether an adequate water supply is guaranteed. It is just as important to recognize an oversupply, which can cause mold, as well as an undersupply, which can lead to desiccation of the plant. Furthermore, a sufficient supply of nutrients is also an important part of keeping the plant healthy.

The color of the leaves is a good indicator of whether there are enough nutrients to ensure good growth. Therefore, in this project not only the soil moisture but also the leaf color of the plant is used to gain knowledge about the health status of the plants.

In the first chapter a self-sufficient device is presented, which transmits the measured data via Bluetooth Low Energy to a base station. The second chapter deals with the measurement of leaf color and the associated limitations. And the last chapter will cover how all data can be collected by a base station for further analysis.

Chapter #1

#1 mini solar cell, #2 rechargeable Ni-MH 100mAh 1.2V battery, #3 ultra low power buck boost power converter to 3.3V, #4 Nordic nRF51822 module, #5 soil moisture sensor

Since nRF51 modules are particularly suitable for ultra low power applications (and I had a few of them lying around), I decided to use them for solar powered standalone devices. Unfortunately, these microcontrollers are already deprecated and the SDK for software development is not maintained anymore. So, using the old nRF SDK 12.3 (https://infocenter.nordicsemi.com/index.jsp?topic=%2Fcom.nordic.infocenter.sdk5.v12.3.0%2Findex.html) from 2017 had to be used accordingly. But this was actually not a big problem, because this device has just two requirements:

record data from ADC and report it in an BLE advertising message to the base station
sleep 99% of the time and consume as less energy as possible

After uploading the firmware and putting all components together the device can be placed next to a plant. But now you have to make sure that the solar cell is not covered by the plant itself, otherwise the harvested energy will not be enough to power the microcontroller.

Chapter #2

Nordic Thingy:53 (highlighted color sensor)

Nordic Thingy:53 has a onboard color sensor which can measure red, green, blue and infrared light. Unfortunately, this sensor need to be placed directly under the leaves and the light needs to shine through them. Otherwise to many shuttered light can be captured by the sensor and distort the measurement. For software development nRF Connect SDK 2.1.0 was used and a simple BLE advertising device was created. You can find the source code and project configuration for VSCode attached.

Recording of artificial illuminated basil leaf. Colors in diagram represent measurements from BH1749 from Thingy:53

Chapter #3

Now it's time to collect the data from solar powered soil moisture sensor and from Thingy:53. A ESP32 has the ability to connect to WiFi network, which allows us to send data in a very convenient way via mqtt to a server. At the same time it can scan for BLE advertising messages. So this is a perfect match for this project. Here a TTGO T5 was used, because it also has a ePaper display for showing the essential status of the plant.

TTGO T5 ESP32 development board and 3D-printed case

The display shows the current soil moisture value provided by the device described in chapter #1 and the leaf color status. Since the measurement of the leaf color was not as reliable as expected (caused by environmental conditions) it shows only "OK" or "not OK" when certain thresholds are reached.

What's next?

improve power consumption for standalone devices
add reference color measurement to compensate change in environmental influences (rising / setting sun, clouds)
add ML to detect anomalies of leaf color
use external color sensor to make recoding of leaf color easier
add external light to make measurement more reliable
scale the project by adding more sensors

fully assembled TTGO T5

Code

#include <zephyr/types.h>
#include <stddef.h>
#include <zephyr/drivers/sensor.h>
#include <zephyr/sys/printk.h>
#include <zephyr/sys/util.h>

#include <zephyr/bluetooth/bluetooth.h>
#include <zephyr/bluetooth/hci.h>

static uint8_t adv_service_uuid[] = {0xAA,0x55,0xAA,0x55};
static uint8_t adv_service_data[] = {0x00,0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};

static const struct bt_data ad[] = {
	BT_DATA(BT_DATA_UUID32_ALL, adv_service_uuid, sizeof(adv_service_uuid)),
	BT_DATA(BT_DATA_SVC_DATA32, adv_service_data, sizeof(adv_service_data)),
};

struct device *dev = NULL;
void Sensor_init(void)
{
	dev = DEVICE_DT_GET_ONE(rohm_bh1749);

	if (!device_is_ready(dev)) {
		printk("Sensor device not ready\n");
		return;
	}
}

void Sensor_Process(void)
{
	int ret;
	struct sensor_value red, green, blue, ir;

	ret = sensor_sample_fetch_chan(dev, SENSOR_CHAN_ALL);
	/* The sensor does only support fetching SENSOR_CHAN_ALL */
	if (ret) {
		printk("sensor_sample_fetch failed ret %d\n", ret);
	return;
	}

	ret = sensor_channel_get(dev, SENSOR_CHAN_RED, &red);
	if (ret) {
		printk("sensor_channel_get failed ret %d\n", ret);
	return;
	}
	printk("BH1749 RED: %d\n", red.val1);

	ret = sensor_channel_get(dev, SENSOR_CHAN_GREEN, &green);
	if (ret) {
		printk("sensor_channel_get failed ret %d\n", ret);
	return;
	}
	printk("BH1749 GREEN: %d\n", green.val1);

	ret = sensor_channel_get(dev, SENSOR_CHAN_BLUE, &blue);
	if (ret) {
		printk("sensor_channel_get failed ret %d\n", ret);
	return;
	}
	printk("BH1749 BLUE: %d\n", blue.val1);

	ret = sensor_channel_get(dev, SENSOR_CHAN_IR, &ir);
	if (ret) {
		printk("sensor_channel_get failed ret %d\n", ret);
	return;
	}
	printk("BH1749 IR: %d\n", ir.val1);

	adv_service_data[0] = red.val1 >> 8;
	adv_service_data[1] = red.val1 & 0xFF;

	adv_service_data[2] = green.val1 >> 8;
	adv_service_data[3] = green.val1 & 0xFF;

	adv_service_data[4] = blue.val1 >> 8;
	adv_service_data[5] = blue.val1 & 0xFF;

	adv_service_data[6] = ir.val1 >> 8;
	adv_service_data[7] = ir.val1 & 0xFF;
}

void main(void)
{
	int err;

	printk("Starting Sensor Advertiser\n");

	/* Initialize the Bluetooth Subsystem */
	err = bt_enable(NULL);
	if (err) {
		printk("Bluetooth init failed (err %d)\n", err);
		return;
	}

	printk("Bluetooth initialized\n");

	/* Start advertising */
	struct bt_le_adv_param adv_params = *(BT_LE_ADV_NCONN_NAME);
	adv_params.interval_min = 100;
	adv_params.interval_max = 100;

	err = bt_le_adv_start(&adv_params, ad, ARRAY_SIZE(ad),
					NULL, 0);
	if (err) {
		printk("Advertising failed to start (err %d)\n", err);
		return;
	}

	Sensor_init();

	while(1) {
		k_sleep(K_MSEC(100));
		Sensor_Process();
		err = bt_le_adv_update_data(ad, ARRAY_SIZE(ad), NULL, 0);
		if (err) {
			printk("Update Advertising failed (err %d)\n", err);
		}
	}
}

Credits

Vincent Münze

2 projects • 1 follower

Comments

Awards

Runner Ups

Smarter Sustainable World Challenge

Plant health monitoring system

Things used in this project

Hardware components

Story

Schematics

basic schematic of standalone solar device

Code

main.c

prj.conf

Credits

Vincent Münze

Comments

Awards

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Plant health monitoring system

Plant health monitoring system

Things used in this project

Hardware components

Story

Schematics

basic schematic of standalone solar device

Code

main.c

prj.conf

Credits

Vincent Münze

Comments

Awards