Reading analog voltage from slow inputs

In this example we will print voltage measured on one of Red Pitaya slow analog inputs that are located on extension connector E2.
Notice that any of four AI pins (0-3) can be used. Web UI

First of all you need new .js file:

pako.js - for decompress data

In index.html add:

<script src="js/jquery-2.1.3.min.js"></script>
<script src="js/pako.js"></script>
<script src="js/app.js"></script>

Our mesurement result will be in this block:

< div id='value'></div>

Add button to read voltage using this string in index.html:

<button id='read_button'>Read</button>

In app.js we should change APP.ws.onmessage() callback. We decompress message and process signals from it.

var data = new Uint8Array(ev.data);
var inflate = pako.inflate(data);
var text = String.fromCharCode.apply(null, new Uint8Array(inflate));
var receive = JSON.parse(text);

if (receive.signals) {

Processing of signals is located in APP.processSignals() function. In this function we get voltage value from signal and print it in Web UI:

var voltage;

for (sig_name in new_signals) {

    if (new_signals[sig_name].size == 0) continue;

    voltage = new_signals[sig_name].value[new_signals[sig_name].size - 1];

    $('#value').text(parseFloat(voltage).toFixed(2) + "V");

By APP.readValue() we send request of reading voltage to controller.

var local = {};
local['READ_VALUE'] = { value: true };
APP.ws.send(JSON.stringify({ parameters: local })); Controller

We read values from pins using controller, so in main.cpp we should make changes. Firstly add signal in global variables:


SIGNAL_SIZE_DEFAULT is our constant. It means how many measurements our signal will send to server. Now it is 1, because each time we need to send to Web UI only one value.

VOLTAGE is a name of our signal. It should be the same, as in app.js, in which we draw it on screen.

0.0f is default value of each measurement.

Also we need reading voltage parameter. It will

CBooleanParameter READ_VALUE("READ_VALUE", CBaseParameter::RW, false, 0);

Its’ default value is false. We will update this parameter in OnNewParams() function:


If READ_VALUE.Value() is true we will read value from AIpin0 and write it to signal:

if (READ_VALUE.Value() == true)
    float val;

    //Read data from pin
    rp_AIpinGetValue(0, &val);

    //Write data to signal
    VOLTAGE[0] = val;

    //Reset READ value

val - is buffer variable, which will get value from AIpin0. After writing data value will be sent to server. We should set READ_VALUE parameter to false.