IoT Relay To Control Appliances Through The Internet Using Smartphone

Electrical appliances such as lights, fans, air-conditioners, TVs, and water pumps are typically operated using manual switches. This system enables these appliances to be controlled over the internet using a smartphone. It combines an ESP-01 Wi-Fi module, the Switchsys MQTT broker (free public version), and the IoT MQTT panel app. The Switchsys MQTT broker implements the MQTT publish/subscribe communication model, enabling communication between the ESP-01 module and the user interface.

The IoT MQTT panel mobile application allows users to send on/off commands and monitor device status in real time from any location with internet access. Commands sent through the app are routed via the MQTT broker to the ESP-01, which processes the subscribed topic and drives the relay accordingly. This enables remote control of connected appliances from virtually anywhere. Fig. 1 shows the author’s prototype, while Table 1 lists the components required to build the system.

The system uses an ESP-01 Wi-Fi module, a relay module, the Switchsys MQTT broker, and the IoT MQTT Panel app. It becomes operational when powered on. The ESP-01 connects to the Wi-Fi network and communicates with the MQTT broker. The user sends on/off commands through the mobile app, which the ESP-01 receives via the broker. Based on the received command, the ESP-01 activates or deactivates the relay to switch the connected bulb on or off.

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System design

In the IoT MQTT Panel app dashboard, there is a single switch to control the relay and an LED indicator to display the relay status.

When Relay1 switch is turned on, the app publishes payload 1 to the topic switchsys/relay1 and sends it to the ESP-01 over the internet via the Switchsys MQTT broker (broker URL: mqtt.switchsys.in, port: 1883). Since the ESP-01 is subscribed to the same topic (switchsys/relay1), it receives payload 1 and sets GPIO0 HIGH, thereby energising the relay.

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After energising the relay, the ESP-01 publishes the relay status to the topic switchsys/relay1/status. This status message is then sent back to the IoT MQTT Panel app through the MQTT broker. In the app, the LED indicator is subscribed to the topic switchsys/relay1/status. Therefore, when payload 1 is received, the LED indicator turns green, indicating that the relay is on.

Similarly, when the relay switch is turned off in the IoT MQTT Panel app, payload 0 is transmitted to the ESP-01 via the topic switchsys/relay1. The ESP-01 then sets GPIO0 LOW, de-energising the relay, and publishes the updated relay status with payload 0 to the topic switchsys/relay1/status. Upon receiving this payload, the LED indicator changes to grey, indicating that the relay is off. Table 2 shows the MQTT topics and payload details used in the project.

Circuit diagram

Fig. 2 shows the circuit diagram of the system. It is built around the ESP-01 Wi-Fi module, the AMS1117-3.3 voltage regulator (5V DC to 3.3V DC), the ULN2003A relay driver IC, the HLK-PM01 230V AC to 5V DC converter module, the HF46F/5-HS1 relay, the 1N4007 diode, and a few other components.

EFY note. This system uses the ESP-01 module, and the GPIO pins are selected accordingly. Other ESP8266-based boards, such as NodeMCU and WeMos D1 Mini, can also be used with this system. In that case, only the ESP-01 module needs to be replaced, and the GPIO pin connections should be modified accordingly.

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