Making an HTTP Request

Devices such as ESP8266-powered Wemos D1, ESP32, or Raspberry Pis are capable of running simple local web servers. One method to control such network-connected devices is for Node-RED to issue a GET request to an HTTP endpoint on that device. Parameters can be appended to the URL to issue commands, and the device can issue a response in the HTML of the reply.

This recipe illustrates how to issue HTTP GET request every minute, which passes two variables representing the hour and minute of the current time. This request is sent to a webpage running on a Wemos D1 Mini, which retrieves the variables sent in the URL string and uses them to set the position of clock hands attached to a dual-shaft stepper motor.

Wiring

Arduino Code

You can find the sketch and associated libraries for this example at https://github.com/playfultechnology/node-redscape/tree/master/Arduino/HTTPRequestClock. The code has been written to run on a WeMos D1 mini device, but can easily be adapted to run on any network-enabled Arduino-esque device.

Flow

[
    {
        "id": "6bba2de2.eb5254",
        "type": "http request",
        "z": "a750a527.4cc178",
        "name": "",
        "method": "GET",
        "ret": "txt",
        "paytoqs": false,
        "url": "http://192.168.1.4?h={{{h}}}&m={{{m}}}",
        "tls": "",
        "persist": false,
        "proxy": "",
        "authType": "",
        "x": 710,
        "y": 260,
        "wires": [
            []
        ]
    },
    {
        "id": "e418a358.a0bfc",
        "type": "function",
        "z": "a750a527.4cc178",
        "name": "Get current time",
        "func": "// Retrieve current time\nvar now = new Date();\n// Extract the hour and minute components\nvar h = now.getHours();\nvar m = now.getMinutes();\n// Add the time elements to the message object\nmsg.h = h;\nmsg.m = m;\n// And pass along the flow\nreturn msg;",
        "outputs": 1,
        "noerr": 0,
        "x": 500,
        "y": 260,
        "wires": [
            [
                "6bba2de2.eb5254"
            ]
        ]
    },
    {
        "id": "3e52d5cb.af4d82",
        "type": "inject",
        "z": "a750a527.4cc178",
        "name": "",
        "topic": "",
        "payload": "",
        "payloadType": "date",
        "repeat": "60",
        "crontab": "",
        "once": false,
        "onceDelay": 0.1,
        "x": 290,
        "y": 260,
        "wires": [
            [
                "e418a358.a0bfc"
            ]
        ]
    },
    {
        "id": "611b7992.0dd6e8",
        "type": "comment",
        "z": "a750a527.4cc178",
        "name": "Trigger every minute",
        "info": "",
        "x": 290,
        "y": 220,
        "wires": []
    },
    {
        "id": "bfbe44f4.c55398",
        "type": "comment",
        "z": "a750a527.4cc178",
        "name": "Set hour and minute",
        "info": "",
        "x": 510,
        "y": 220,
        "wires": []
    },
    {
        "id": "e4719459.c39c7",
        "type": "comment",
        "z": "a750a527.4cc178",
        "name": "Pass time parameters to GET request",
        "info": "",
        "x": 790,
        "y": 220,
        "wires": []
    }
]