How to Control a Remote GSM MQTT Device Using a Mobile App

This guide walks you through controlling a remote IoT device equipped with a GSM-based MQTT module (e.g., A7670C, SIM800L, SIM900A) using your mobile phone via HiveMQ Cloud.

Use this if:

You want to prototype remote control via MQTT using cellular modules.
You are using a mobile app (like MQTT Dash or IoT MQTT Panel) to publish control commands.

Instructions

Prerequisites

Component	Description

Component	Description
GSM module	A7670C, SIM800L, SIM900, or equivalent
SIM card	With active data service
MQTT Broker	HiveMQ Cloud Free Plan
Mobile App	MQTT Dash, IoT MQTT Panel, or similar
Credentials	Broker hostname, port, username, password

Step 1: Set Up HiveMQ Cloud

Create a free account at HiveMQ Cloud.
Create a new MQTT cluster.
Note the following parameters:
- Hostname
- Port: 8883 (TLS)
- Username and password

TLS is required for the free plan.

Step 2: Configure GSM Module to Connect to MQTT Broker

Example setup for A7670C (adapt as needed for your hardware):

AT+CGATT=1
AT+CGDCONT=1,"IP","your.apn.com"
AT+NETOPEN
AT+IPADDR

AT+MQTTUSERCFG=0,1,"client_id","username","password",0,0,""
AT+MQTTCONN=0,"<broker.hivemq.cloud>",8883,1
AT+MQTTSUB=0,"/device/control",1

Ensure that the firmware supports MQTT over TLS.

Step 3: Configure Mobile App to Send Commands

Use MQTT Dash or IoT MQTT Panel.

Create a new MQTT connection:
- Host: your HiveMQ Cloud hostname
- Port: 8883
- TLS: enabled
- Username and password: from HiveMQ Cloud
Add a button widget:
- Topic: /device/control
- Payload: ON or OFF

Pressing the button will send the corresponding command to the GSM MQTT device.

Troubleshooting

Issue	Recommendation

Issue	Recommendation
No response from device	Confirm topic names match exactly between mobile and device
Connection failure	Check SIM card, APN, broker hostname, port, and credentials
GSM module does not support TLS	Consider using a broker that allows non-TLS connections for testing only