Trigger using MQTT and Node-Red

This guide walks you through configuring and using MQTT communication to trigger your OV20 camera using Node-RED. By the end, you'll be able to remotely trigger image capture and processing through MQTT messages.

Overview

MQTT (Message Queuing Telemetry Transport) is a lightweight messaging protocol ideal for IoT devices. Using MQTT with your OV20 camera enables remote triggering and communication with other systems in your network. This approach is particularly useful in production environments where you need to integrate the camera with other automated systems.

Prerequisites

Before you begin, ensure you have:

• OV20 camera connected to your network
• Node-RED installed and configured
• An MQTT broker set up (You can set it up in Node-Red)
• Basic understanding of Node-RED flows
• Camera configured with a working recipe
• Trigger in the camera needs to be setup as Manuel trigger in image setup.

Setting Up the MQTT Trigger Flow

1. Configure the MQTT Broker Connection

1. Open your Node-RED editor in your browser
2. Drag an MQTT-in node from the palette to your workspace
3. Double-click the node to open its properties
4. Click the pencil icon next to the Server field to add a new broker
5. Configure the broker with these settings:

• Name: Camera MQTT Broker
• Server: Your broker's IP address (e.g., 192.168.1.100) or localhost
• Port: 1883 (default MQTT port)
• Client ID: Generate a unique ID (You can leave it empty for autogenerate)
  
  

6. Click Add to save the broker configuration

2. Configure the flow

For the mqtt request to work there needs to me a message object sent to the different topics, for that we create a flow that explains the setup, in which there needs to be 2 messages, the first one is to put the camera in a HMI mode, and the second one asking to trigger the camera.

1. Configure the [Inject] node

   • Double click on the inject node
   • [msg.payload]: It can be left as a timestamp, as the inject will work on this excersie as the start point or pulse for the trigger.
   • Save

2. Configure the first [Change] node

   • Double click on the change node
   • Setup these 2 rules:
   • Click on add -> SET -> msg.topic to the value of : [stream_mode/set]
   • Click on add again -> SET -> msg.payload to the value of: [HMI_MODE]
   • Save
     

3. Configure the second [Change] node

   • Double click on the change node
   • Setup these 2 rules:
   • Click on add -> SET -> msg.topic to the value of : [hmi/?/capture_mode]
   • Click on add again -> SET -> msg.payload to the value of: [single]
   • Save
     

3. Connect to the [Mqtt In] node you already configured

Testing and Verification

To verify your setup works correctly:

1. Click the button on the inject node to trigger the Mqtt request
2. Check the debug panel
3. Verify that the camera has taken a picture, a easy way to confirm it will be that there is a new message on debug from the AllBlocksOutput

Complete Flow Example

For reference, here's the complete flow JSON that you can import into node-RED:

[
    {
        "id": "80474d6fc128742d",
        "type": "mqtt out",
        "z": "6e6e08c3c76c7987",
        "name": "",
        "topic": "",
        "qos": "0",
        "retain": "",
        "respTopic": "",
        "contentType": "",
        "userProps": "",
        "correl": "",
        "expiry": "",
        "broker": "5628611a59df452b",
        "x": 850,
        "y": 860,
        "wires": []
    },
    {
        "id": "51e487a95039d080",
        "type": "change",
        "z": "6e6e08c3c76c7987",
        "name": "Set Payload 1",
        "rules": [
            {
                "p": "topic",
                "t": "set",
                "pt": "msg",
                "to": "stream_mode/set",
                "tot": "str"
            },
            {
                "p": "payload",
                "t": "set",
                "pt": "msg",
                "to": "HMI_MODE",
                "tot": "str"
            }
        ],
        "action": "",
        "property": "",
        "from": "",
        "to": "",
        "reg": false,
        "x": 680,
        "y": 860,
        "wires": [
            [
                "80474d6fc128742d"
            ]
        ]
    },
    {
        "id": "a6d5a4132ed1f39d",
        "type": "change",
        "z": "6e6e08c3c76c7987",
        "name": "Set Payload 2",
        "rules": [
            {
                "p": "topic",
                "t": "set",
                "pt": "msg",
                "to": "hmi/10/capture_mode",
                "tot": "str"
            },
            {
                "p": "payload",
                "t": "set",
                "pt": "msg",
                "to": "single",
                "tot": "str"
            }
        ],
        "action": "",
        "property": "",
        "from": "",
        "to": "",
        "reg": false,
        "x": 680,
        "y": 900,
        "wires": [
            [
                "80474d6fc128742d"
            ]
        ]
    },
    {
        "id": "25f5166b2886fcc7",
        "type": "delay",
        "z": "6e6e08c3c76c7987",
        "name": "",
        "pauseType": "delay",
        "timeout": "10",
        "timeoutUnits": "milliseconds",
        "rate": "1",
        "nbRateUnits": "1",
        "rateUnits": "second",
        "randomFirst": "1",
        "randomLast": "5",
        "randomUnits": "seconds",
        "drop": false,
        "allowrate": false,
        "outputs": 1,
        "x": 510,
        "y": 900,
        "wires": [
            [
                "a6d5a4132ed1f39d"
            ]
        ]
    },
    {
        "id": "1435d7b97a321f86",
        "type": "inject",
        "z": "6e6e08c3c76c7987",
        "name": "",
        "props": [
            {
                "p": "payload"
            },
            {
                "p": "topic",
                "vt": "str"
            }
        ],
        "repeat": "",
        "crontab": "",
        "once": false,
        "onceDelay": 0.1,
        "topic": "",
        "payload": "",
        "payloadType": "date",
        "x": 320,
        "y": 860,
        "wires": [
            [
                "25f5166b2886fcc7",
                "51e487a95039d080"
            ]
        ]
    },
    {
        "id": "5628611a59df452b",
        "type": "mqtt-broker",
        "name": "",
        "broker": "localhost",
        "port": "1883",
        "clientid": "",
        "autoConnect": true,
        "usetls": false,
        "protocolVersion": "4",
        "keepalive": "60",
        "cleansession": true,
        "birthTopic": "",
        "birthQos": "0",
        "birthRetain": "false",
        "birthPayload": "",
        "birthMsg": {},
        "closeTopic": "",
        "closeQos": "0",
        "closeRetain": "false",
        "closePayload": "",
        "closeMsg": {},
        "willTopic": "",
        "willQos": "0",
        "willRetain": "false",
        "willPayload": "",
        "willMsg": {},
        "userProps": "",
        "sessionExpiry": ""
    }
]