Trouble inserting dashboard slider value into JSON payload

General
1

Hey All,
I've got a dashboard slider that sends 0-255 to an esp8266 using JSON. I can do this from an inject mode with the following payload, it works as intended.

{"modeBrightness" : 50}  // renders 50

Next I want to send the brightness from a slider on the dashboard. I'm trying to add it to JSON with a change node with the following code.

{"modeBrightness" : "{{topic}}"}  // renders {{topic}}  

{"modeBrightness" : "{{payload}}"}  // renders {{payload}}

How can I get the slider values into my JSON payload?
Thx
Rich

[
    {
        "id": "6e4a0e1c3f08a293",
        "type": "debug",
        "z": "cf08cb9713ba9cda",
        "name": "debug 341",
        "active": true,
        "tosidebar": true,
        "console": false,
        "tostatus": false,
        "complete": "false",
        "statusVal": "",
        "statusType": "auto",
        "x": 410,
        "y": 220,
        "wires": []
    },
    {
        "id": "49ed4223b39cd05d",
        "type": "change",
        "z": "cf08cb9713ba9cda",
        "name": "",
        "rules": [
            {
                "t": "set",
                "p": "payload",
                "pt": "msg",
                "to": "{\"modeBrightness\" : \"{{topic}}\"}",
                "tot": "json"
            }
        ],
        "action": "",
        "property": "",
        "from": "",
        "to": "",
        "reg": false,
        "x": 240,
        "y": 80,
        "wires": [
            [
                "6e4a0e1c3f08a293",
                "902ba5af9d02cea1"
            ]
        ]
    },
    {
        "id": "f77c465a8c64faee",
        "type": "ui_slider",
        "z": "cf08cb9713ba9cda",
        "name": "",
        "label": "brightness",
        "tooltip": "",
        "group": "65963440961b63cc",
        "order": 6,
        "width": 0,
        "height": 0,
        "passthru": true,
        "outs": "end",
        "topic": "topic",
        "topicType": "msg",
        "min": "0",
        "max": "255",
        "step": 1,
        "className": "",
        "x": 70,
        "y": 80,
        "wires": [
            [
                "49ed4223b39cd05d"
            ]
        ]
    },
    {
        "id": "65963440961b63cc",
        "type": "ui_group",
        "name": "HANGING LAMP",
        "tab": "f3a8a67ff0904e39",
        "order": 3,
        "disp": true,
        "width": "6",
        "collapse": true,
        "className": ""
    },
    {
        "id": "f3a8a67ff0904e39",
        "type": "ui_tab",
        "name": "HOME",
        "icon": "dashboard",
        "order": 1,
        "disabled": false,
        "hidden": false
    }
]
2

In the change node select JSONata J: not json, you can use

{"modeBrightness" :  $$.payload}

Or use a template node, set to output js object, and you what you had minus the quotes.

{"modeBrightness" : {{payload}}}
3

Or you can do it like this

image

You can't set msg.payload.modeBrightness directly as it is currently a number, so you can't add a property to it. msg.temp does not exist so the change node allows you to create it as an object, then move it into the payload.