Trigger using MQTT and Node-Red
- 28 Apr 2025
- Imprimir
- DF
Trigger using MQTT and Node-Red
- Actualizado el 28 Apr 2025
- Imprimir
- DF
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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.
Note
If you haven't set up MQTT communication yet, refer to the Setting Up MQTT Communication guide first.
Setting Up the MQTT Trigger Flow
1. Configure the MQTT Broker Connection
- Open your Node-RED editor in your browser
- Drag an MQTT-in node from the palette to your workspace
- Double-click the node to open its properties
- Click the pencil icon next to the Server field to add a new broker
- 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)
- 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.
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
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
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
Important
The unique recipe number is not the same as the PLC recipe number. The recipe number can be found at the top of the URL of an active recipe. It will change depending on the recipe, and there won't be two that are the same.
- Connect to the [Mqtt In] node you already configured
Testing and Verification
To verify your setup works correctly:
- Click the button on the inject node to trigger the Mqtt request
- Check the debug panel
- 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": ""
}
]
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