Read analog voltage on slow analog inputs

Description

This example shows how to measure the analog voltage of slow analog inputs on the Red Pitaya extension connector. The analog inputs on the Red Pitaya are rated from 0 to 3.3 Volts.

Required hardware

• Red Pitaya device

• R1 10k potentiometer

Wiring example:

Required software

• 2.00-23 or higher OS

Note

This code is written for 2.00-23 or higher OS. For older OS versions, please check when specific commands were released (a note is added to each command introduced in 2.00 or higher verisons).

Circuit

SCPI Code Examples

Code - MATLAB®

The code is written in MATLAB. TCP client communication is used to establish socket communication with Red Pitaya, then SCPI commands are sent to configure the various Red Pitaya peripherals. Copy the code below into the MATLAB editor, save the project and press the Run button. Tested on MATLAB 2024b.

close all;
clc;

%% Define Red Pitaya as TCP/IP object
IP = 'rp-f0a235.local';             % Input IP of your Red Pitaya...
port = 5000;
RP = tcpclient(IP, port);

%% Open connection with your Red Pitaya
RP.ByteOrder = 'big-endian';
configureTerminator(RP,'CR/LF');

%% Setup
a = 1;              % iteration
v0 = [];            % Voltage arrays
v1 = [];
v2 = [];
v3 = [];
f = gcf;            % Figure
hold on;

volts0 = str2double(writeread(RP,'ANALOG:PIN? AIN0'));
volts1 = str2double(writeread(RP,'ANALOG:PIN? AIN1'));
volts2 = str2double(writeread(RP,'ANALOG:PIN? AIN2'));
volts3 = str2double(writeread(RP,'ANALOG:PIN? AIN3'));

%% Plotting data
while (a < 500)
    v0(a) = str2double(writeread(RP,'ANALOG:PIN? AIN0'));
    v1(a) = str2double(writeread(RP,'ANALOG:PIN? AIN1'));
    v2(a) = str2double(writeread(RP,'ANALOG:PIN? AIN2'));
    v3(a) = str2double(writeread(RP,'ANALOG:PIN? AIN3'));

    % Plot
    if (a < 150)
        plot(v0, 'LineWidth', 2, 'Color', [0 0.4470 0.7410]);
        plot(v1, 'LineWidth', 2, 'Color', [0.8500 0.3250 0.0980]);
        plot(v2, 'LineWidth', 2, 'Color', [0.9290 0.6940 0.1250]);
        plot(v3, 'LineWidth', 2, 'Color', [0.4660 0.6740 0.1880]);
    else
        clf;
        plot(v0(end-149:end), 'LineWidth', 2, 'Color', [0 0.4470 0.7410]);
        plot(v1(end-149:end), 'LineWidth', 2, 'Color', [0.8500 0.3250 0.0980]);
        plot(v2(end-149:end), 'LineWidth', 2, 'Color', [0.9290 0.6940 0.1250]);
        plot(v3(end-149:end), 'LineWidth', 2, 'Color', [0.4660 0.6740 0.1880]);
    end

    % Plot settings
    grid ON;
    xlabel('Samples');
    ylim([0 3.5]);
    ylabel('{\itU} [V]');
    title('Voltage');
    legend('v0','v1','v2','v3');

    pause(0.01);
    a = a+1;
end

%% Close connection with Red Pitaya
clear RP;

Code - Python

#!/usr/bin/env python3

import sys
import redpitaya_scpi as scpi

IP = 'rp-f066c8.local'

rp = scpi.scpi(IP)

for i in range(4):
    rp.tx_txt('ANALOG:PIN? AIN' + str(i))
    value = float(rp.rx_txt())
    print ("Measured voltage on AI["+str(i)+"] = "+str(value)+"V")

rp.close()

Note

The Python functions are accessible with the latest version of the redpitaya_scpi.py document available on our GitHub. The functions represent a quality-of-life improvement as they combine the SCPI commands in an optimal order and also check for improper user inputs. The code should function at approximately the same speed without them.

For further information on functions please consult the redpitaya_scpi.py code.

Code - LabVIEW

• Download Example

API Code Examples

Note

The API code examples don’t require the use of the SCPI server. Instead, the code should be compiled and executed on the Red Pitaya itself (inside Linux OS). Instructions on how to compile the code and other useful information are here.

Code - C++ API

/* Read analog voltage on slow analog input */

#include <stdio.h>
#include <stdlib.h>

#include "rp.h"

int main (int argc, char **argv) {
    float value [4];

    // Initialization of API
    if (rp_Init() != RP_OK) {
        fprintf(stderr, "Red Pitaya API init failed!\n");
        return EXIT_FAILURE;
    }

    // Measure each XADC input voltage
    for (int i=0; i<4; i++) {
        rp_AIpinGetValue(i, &value[i]);
        printf("Measured voltage on AI[%i] = %1.2fV\n", i, value[i]);
    }

    // Releasing resources
    rp_Release();

    return EXIT_SUCCESS;
}

Code - Python API

#!/usr/bin/python3
import rp

analog_in = [rp.RP_AIN0, rp.RP_AIN1, rp.RP_AIN2, rp.RP_AIN3]

# Initialize the interface
rp.rp_Init()

# Reset analog pins
rp.rp_ApinReset()

#####! Choose one of two methods, comment the other !#####

#! METHOD 1: Reading all values and selecting the appropriate

#for i in range(4):
#    # rp_ApinGetValue returns an array - [0, Input voltage in V, Input voltage RAW]
#    value = rp.rp_ApinGetValue(analog_in[i])[1]
#    print (f"Measured voltage on AI[{i}] = {value} V")


#! METHOD 2: Read just analog inputs

for i in range(4):
    # rp_AIpinGetValue returns an array - [0, Input voltage in V, Input voltage RAW]
    value = rp.rp_AIpinGetValue(i)[1]
    print (f"Measured voltage on AI[{i}] = {value} V")

# Release resources
rp.rp_Release()