Feasibility Q - hit an HTTP end point, interpret the returned JSON to turn/on/off an output

Hi,
I have a use case with a solar inverter + homebrew arduino which presents the Inverter control variables as an HTTP conversation.

e.g. To ask the inverter for current solar generation and battery levels I might send: http://solis.local/R?a=33057.2,33139
33057.2 and 33139 are specific registers being requested.

The response will be JSON list thus: {"data":[254,62]}

Meaning 254 watts and 62%

Ideally if I could do this in a shelly script then I could drive intellegent mains switching outputs depending on various power generation scenarios. Shelly would loop periodically making the above call and deciding how to change ouputs depending on the result- perhaps turning something on when the batteries are full, or when solar is above a certain level.

Has anyone worked with an HTTP conv like the above before - can you give me some hints please?


My original plan was a wemosD1 arduino (or similar) for the comms part with an off the shelf mains relay - however just been introduced to the shelly line of products which might already have the right combination of hardware/software.

Many thanks;

Thank you

Yes - thats looks promising - Shelly.call is the key function.

Looks like I'll order one and have a play.

Feedback - this worked really well;

I bought a Shelly 1 Plus and setup to talk to my custom solar inverter as in the top post.

This code, as an initial starting point, works great- polls the HTTP end point every 5 minutes and switches accordingly.

Very nice component - saved me building one from scratch!
Thank you for the help above.

(Looks like it needs a specific IP address and cannot resolve MDNS)

/*
Read Solis inverter battery SOC register to control the ouput switch
Only turn on if the battery is over a threshold charge


Uses a custom inverter server side interface


Use case
Prevent simple immersion diverter, e.g. SOLIC200 from diverting
solar power before the battery is full


Todo
Local button should override - either toggle or 1 hour on


R.Lincoln  March 2023


*/


let inverterIP = '192.168.1.143';   // Fixed inverter IP (mdns not working)
let socThreshold = 80;              // on above this % full
let checkSeconds = 60 *5;           // seconds between checks


//  Call the inverter, retreive 33139 - Battery state of charge %
//  http://192.168.1.143/R?a=33139
//
function getSOC() {
Shelly.call("HTTP.GET",
{ url: 'http://' + inverterIP + '/R?a=33139'},
readJSON,
null);
}


//  Process the response JSON
//  e.g. {"data":[64]}
//  If the data value is over the threshold - turn on the switch
//
function readJSON(res, error_code, error_msg, ud) {
//  Ignore any http error
if (res.code !== 200) return;


//  Extract the  JSON value
let body = JSON.parse(res.body);
let soc = body.data[0];


//  Compare with the threshold
let on = soc >= socThreshold;
print('Battery:', soc, '%, on:', on);


//  Set the local switch
Shelly.call("switch.set",
{ id: 0, on: on },
null, null);
}


//  Periodically check the percentage
//
print('Starting');
getSOC();
let timer = Timer.set(1000 *checkSeconds, true, getSOC, null);