Remotely Controlled Plant Watering System Using nRF7002 Dk

Setup Development Environment

Application Development

We are using the MQTT sample code from the nordic/ncs/v2.3.0/nrf/samples/net/mqtt from the SDK. MQTT is a messaging protocol for the Internet of Things (IoT) which is designed as an extremely lightweight publish/subscribe messaging transport that is ideal for connecting remote devices with minimal network bandwidth. The MQTT sample communicates with an MQTT broker over Wi-Fi using the nRF7002 DK. We will be using the Home Assistant,  an open-source software for home automation, for the MQTT broker services and dashboard to display the application user interface.

The sample has a modular structure, where each module has a defined scope of responsibility. The communication between modules is handled by the Zephyr message bus (zbus) using messages that are passed over channels. If a module has internal state handling, it is implemented using the Zephyr State Machine Framework.  The default sample has 4 main modules: Network WiFI, Sampler, Trigger, and Transport.  The Sampler module has been modified to sample soil moisture data over the ADC channel. The Trigger module triggers the sampler to publish the data at configurable intervals.  To control the water pump, the Water Switch module has been added to the modules stack that receives the subscription payload from the Transport module. The following figure illustrates the relationship between modules, channels, and network stacks in the sample.

To enable ADC and GPIO support we have added the following lines to the prj.conf file.

# ADC
CONFIG_ADC=y
CONFIG_ADC_ASYNC=y
CONFIG_ADC_LOG_LEVEL_INF=y
 
# Water pump Digital Pin
CONFIG_GPIO=y

Also, we have created an overlay file nrf7002dk_nrf5340_cpuapp.overlay with the following contents.

&adc {
        status = "okay";
};

The Water Switch module (src/modules/water_switch) code is given below.

#include <zephyr/kernel.h>
#include <zephyr/logging/log.h>
#include <zephyr/zbus/zbus.h>
#include <zephyr/drivers/gpio.h>
#include "message_channel.h"
 
/* Register log module */
LOG_MODULE_REGISTER(water_switch);
 
#define WATER_PUMP_PIN  10 // P1.10 (D8)
const static struct device *digital_pin_dev;
static bool configured = false;
 
void configure() 
{
        digital_pin_dev  = DEVICE_DT_GET(DT_NODELABEL(gpio1));
        if (!digital_pin_dev) {
            LOG_ERR("device gpio1 not foundn");
            return;
        }
 
        if (!device_is_ready(digital_pin_dev)) {
            LOG_ERR("GPIO controller not ready");
            return;
        }
 
        gpio_pin_configure(digital_pin_dev, WATER_PUMP_PIN, GPIO_OUTPUT); 
}
 
void water_switch_callback(const struct zbus_channel *chan)
{
	int err = 0;
	const enum water_switch_status *status;
 
	if (&WATER_SWITCH_CHAN == chan) {
                if (!configured) {
                    configure();
                    configured = true;
	            LOG_INF("GPIO pin configured");
                }
 
		/* Get network status from channel. */
		status = zbus_chan_const_msg(chan);
 
	        LOG_INF("status =  %d", *status);
 
		switch (*status) {
		case SWITCH_OFF:
                        err = gpio_pin_set(digital_pin_dev, WATER_PUMP_PIN, 0);
			if (err) {
				LOG_ERR("digital pin, error: %d", err);
			} else {
	                    LOG_INF("SWITCH_OFF:  %d", err);
                        }
			break;
		case SWITCH_ON:
                        err = gpio_pin_set(digital_pin_dev, WATER_PUMP_PIN, 1);
			if (err) {
				LOG_ERR("digital pin, error: %d", err);
			} else {
	                    LOG_INF("SWITCH_ON:  %d", err);
                        }
			break;
		default:
			LOG_ERR("Unknown event: %d", *status);
			break;
		}
	}
}
 
/* Register listener - water_switch_callback will be called everytime a channel that the module listens on
 * receives a new message.
 */
ZBUS_LISTENER_DEFINE(water_switch, water_switch_callback);

In the src/modules/transport  file, we have modified the on_mqtt_publish function to pass the subscription call to the Water Switch module over the Zbus channel.

static void on_mqtt_publish(struct mqtt_helper_buf topic, struct mqtt_helper_buf payload)
{
        LOG_INF("Received payload: %.*s on topic: [%.*s]", payload.size,
                                                         payload.ptr,
                                                         topic.size,
                                                         topic.ptr);
        enum water_switch_status status;
        if (payload.size == 1) {
            if (payload.ptr[0] == 48) {
                LOG_INF("SWITCH_OFF");
                status = SWITCH_OFF;
            }
 
            if (payload.ptr[0] == 49) {
                LOG_INF("SWITCH_ON");
                status = SWITCH_ON;
            }
        }
 
        int err = zbus_chan_pub(&WATER_SWITCH_CHAN, &status, K_SECONDS(1));
 
        if (err) {
                LOG_ERR("zbus_chan_pub, error: %d", err);
                SEND_FATAL_ERROR();
        }
}

Setup Home Assistant

There are many ways to install the Home Assistant Operating System. Please follow the instructions at the link below.

https://www.home-assistant.io/installation/

I am using a Home Assistant Virtual Machine on a macOS host. After starting up the VM instance, we can access the Home Assistant portal using a web browser at http://homeassistant.local:8123.  The Home Assistant provides a few options to set up an MQTT broker. I am using EMQX which can be installed by searching at Settings > Add-ons > Add-on Store. Another option is to install Mosquitto but I had to install EMQX because it allows me to configure the broker without any username/password. I couldn't find an easy way to provide a username/password in the sample MQTT application so I chose EMQX. After installing EMQX, we need to set up an MQTT integration by going to Settings > Devices & Services > Add Integration and searching for MQTT.   After adding the MQTT integration click on Configure and set the values as shown below.

Also, we always need to restart the Home Assistant after any configuration changes by clicking Settings > Top Right Kebab menu > Restart Home Assistant. 

We have added two UI cards in the Overview > Dashboard, a Gauge card for displaying the soil moisture sensor data and a Button card for controlling the water pump. We need to configure the card entity using configuration files that can be accessed and edited using the SAMBA share at the host computer. The following configuration is added to the configuration.yaml.

 
mqtt:
  sensor:
    - name: "Soil Moisture"
      state_topic: "/myhome/plant/status"
      unit_of_measurement: "%"
      value_template: "{{ value_json.soil_moisture | float }}"
  switch:
    - name: "Watering Switch"
      command_topic: "/myhome/plant/watering"
      qos: 1
      payload_on: 1
      payload_off: 0 
      retain: true

We have added a configuration in the config/automations.yaml file for automatically switching off the Water Switch after 5 seconds of manual click and triggering the switch automatically if soil moisture is below 35%.

- trigger:
    - platform: state
      entity_id: switch.watering_switch
      to: "on"
      for:
        milliseconds: 5000
  action:
    service: switch.turn_off
    target:
      entity_id: switch.watering_switch
- trigger:
    - platform: numeric_state
      entity_id: sensor.soil_moisture
      below: 35
  action:
    service: switch.turn_on
    target:
      entity_id: switch.watering_switch