Instant signal acquisition

Description

This example shows how to instantly acquire 16k samples of a signal on fast analog inputs. The time length of the acquired signal depends on the time scale of a buffer that can be set with a decimation factor. The decimations and time scales of a buffer are given in the sample rate and decimation. Voltage and frequency ranges depend on the Red Pitaya model.

Required hardware

• Red Pitaya device

• Signal (function) generator

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

Note

With the latest OS versions you can use ACQ:DEC:F <decimation_factor> command for more precise control over the acquisition. The decimation factor can be any of [1, 2, 4, 8, 16, 17, 18, 19, ..., 65535, 65536].

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.

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

dec = 1;
trig_lvl = 0.1;
gain = 'LV';
% coupling = 'AC';      % SIGNALlab 250-12 only
trig_dly = 0;
acq_trig = 'CH1_PE';

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

% Reset Acquisition
writeline(RP,'ACQ:RST');

%% ACQUISITION
% Set decimation vale (sampling rate) in respect to the
% acquired signal frequency

writeline(RP, append('ACQ:DEC:Factor ', num2str(dec)));

% Set trigger delay to 0 samples
% 0 samples delay set trigger to center of the acquired data buffer
% The triggering moment is in the center (8192nd sample)
% Samples from left to the center were acquired before the trigger
% Samples from center to the right were acquired after the trigger

writeline(RP, append('ACQ:TRig:DLY ', num2str(trig_dly)));

% SIGNALlab 250-12 has an option to set the external trigger level threshold
% writeline(RP, append('ACQ:TRig:EXT:LEV ', trig_lvl));

%% Start & Trigg
% Trigger source command must be set after ACQ:START
% Set trigger to source 1 positive edge

writeline(RP,'ACQ:START');

% After acquisition is started, some time delay is needed in order to acquire fresh samples in to buffer
% Here we use a time delay of one second but you can calculate exact value taking in to account buffer
% length and sampling rate

pause(1);

% Immediately trigger the acquisition
writeline(RP,'ACQ:TRig NOW');

% % This loop is not needed as we triggered the acquisition manually
% while 1
%     trig_rsp = writeread(RP,'ACQ:TRig:STAT?')
%     if strcmp('TD', trig_rsp(1:2))  % Read only TD
%         break;
%     end
% end

% wait for fill adc buffer
while 1
    fill_state = writeread(RP,'ACQ:TRig:FILL?')
    if strcmp('1', fill_state(1:1))
        break;
    end
end

% Read data from buffer
data_str   = writeread(RP,'ACQ:SOUR1:DATA?');
data_str_2 = writeread(RP,'ACQ:SOUR2:DATA?');

% Convert values to numbers.
data   = str2num(data_str  (2:length(data_str)  -1));
data_2 = str2num(data_str_2(2:length(data_str_2)-1));

hold on
plot(data)
plot(data_2,'r')
grid on
ylabel('Voltage / V')
xlabel('Samples')

clear RP;

Code - Python

Using SCPI commands:

#!/usr/bin/env python3

import sys
import redpitaya_scpi as scpi
import matplotlib.pyplot as plot

IP = 'rp-f066c8.local'

rp = scpi.scpi(IP)

rp.tx_txt('ACQ:RST')

rp.tx_txt('ACQ:DEC 4')
rp.tx_txt('ACQ:START')
rp.tx_txt('ACQ:TRig NOW')

while 1:
    rp.tx_txt('ACQ:TRig:STAT?')
    if rp.rx_txt() == 'TD':
        break

## ! OS 2.00 or higher only ! ##
while 1:
    rp.tx_txt('ACQ:TRig:FILL?')
    if rp.rx_txt() == '1':
        break

rp.tx_txt('ACQ:SOUR1:DATA?')
buff_string = rp.rx_txt()
buff_string = buff_string.strip('{}\n\r').replace("  ", "").split(',')
buff = list(map(float, buff_string))

plot.plot(buff)
plot.ylabel('Voltage')
plot.show()

Using functions:

#!/usr/bin/env python3

import sys
import redpitaya_scpi as scpi
import matplotlib.pyplot as plot

IP = 'rp-f066c8.local'

rp = scpi.scpi(IP)

rp.tx_txt('ACQ:RST')

dec = 4

# Function for configuring Acquisition
rp.acq_set(dec)

rp.tx_txt('ACQ:START')
rp.tx_txt('ACQ:TRig NOW')

while 1:
    rp.tx_txt('ACQ:TRig:STAT?')
    if rp.rx_txt() == 'TD':
        break

## ! OS 2.00 or higher only ! ##
while 1:
    rp.tx_txt('ACQ:TRig:FILL?')
    if rp.rx_txt() == '1':
        break

# function for Data Acquisition
buff = rp.acq_data(1, convert= True)

plot.plot(buff)
plot.ylabel('Voltage')
plot.show()

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.

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

/* Red Pitaya C++ API example of Instantly acquiring a signal on a specific channel */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include "rp.h"

int main(int argc, char **argv){

    /* Print error, if rp_Init() function failed */
    if(rp_Init() != RP_OK){
        fprintf(stderr, "Rp api init failed!\n");
    }

    /* Reset Generation and Acquisition */
    rp_GenReset();
    rp_AcqReset();

    /* Generation */
    /*LOOB BACK FROM OUTPUT 2 - ONLY FOR TESTING*/
    rp_GenFreq(RP_CH_1, 20000.0);
    rp_GenAmp(RP_CH_1, 1.0);
    rp_GenWaveform(RP_CH_1, RP_WAVEFORM_SINE);
    rp_GenOutEnable(RP_CH_1);

    /* Acquisition */
    uint32_t buff_size = 16384;
    float *buff = (float *)malloc(buff_size * sizeof(float));

    rp_AcqSetDecimation(RP_DEC_8);
    rp_AcqSetTriggerLevel(RP_CH_1, 0.5);         // Trig level is set in Volts while in SCPI
    rp_AcqSetTriggerDelay(0);

    // There is an option to select coupling when using SIGNALlab 250-12
    // rp_AcqSetAC_DC(RP_CH_1, RP_AC);           // enables AC coupling on Channel 1

    // By default LV level gain is selected
    rp_AcqSetGain(RP_CH_1, RP_LOW);              // user can switch gain using this command

    rp_AcqStart();

    /* After the acquisition is started some time delay is needed to acquire fresh samples into buffer
    Here we have used a time delay of one second but you can calculate the exact value taking into account buffer
    length and sampling rate */

    sleep(1);
    rp_AcqSetTriggerSrc(RP_TRIG_SRC_NOW);
    rp_acq_trig_state_t state = RP_TRIG_STATE_TRIGGERED;

    while(1){
        rp_AcqGetTriggerState(&state);
        if(state == RP_TRIG_STATE_TRIGGERED){
            break;
        }
    }

    %%! OS 2.00 or higher only !%%
    bool fillState = false;
    while(!fillState){
        rp_AcqGetBufferFillState(&fillState);
    }

    rp_AcqGetOldestDataV(RP_CH_1, &buff_size, buff);
    int i;
    for(i = 0; i < buff_size; i++){
        printf("%f\n", buff[i]);
    }

    /* Releasing resources */
    free(buff);
    rp_Release();
    return 0;
}

Code - Python API

#!/usr/bin/python3

import time
import numpy as np
import rp


#? Possible decimations:
#?  RP_DEC_1, RP_DEC_2, RP_DEC_4, RP_DEC_8, RP_DEC_16 , RP_DEC_32 , RP_DEC_64 ,
#?  RP_DEC_128, RP_DEC_256, RP_DEC_512, RP_DEC_1024, RP_DEC_2048, RP_DEC_4096, RP_DEC_8192,
#?  RP_DEC_16384, RP_DEC_32768, RP_DEC_65536

dec = rp.RP_DEC_1

trig_lvl = 0.5
trig_dly = 0

#? Possible acquisition trigger sources:
#?  RP_TRIG_SRC_DISABLED, RP_TRIG_SRC_NOW, RP_TRIG_SRC_CHA_PE, RP_TRIG_SRC_CHA_NE, RP_TRIG_SRC_CHB_PE,
#?  RP_TRIG_SRC_CHB_NE, RP_TRIG_SRC_EXT_PE, RP_TRIG_SRC_EXT_NE, RP_TRIG_SRC_AWG_PE, RP_TRIG_SRC_AWG_NE,
#?  RP_TRIG_SRC_CHC_PE, RP_TRIG_SRC_CHC_NE, RP_TRIG_SRC_CHD_PE, RP_TRIG_SRC_CHD_NE

acq_trig_sour = rp.RP_TRIG_SRC_NOW
N = 16384

# Initialize the interface
rp.rp_Init()

# Reset Acquisition
rp.rp_AcqReset()

##### Acquisition #####
# Set Decimation
rp.rp_AcqSetDecimation(dec)


# Set trigger level and delay
rp.rp_AcqSetTriggerLevel(rp.RP_T_CH_1, trig_lvl)
rp.rp_AcqSetTriggerDelay(trig_dly)

# Start Acquisition
print("Acq_start")
rp.rp_AcqStart()

# Specify trigger - immediately
rp.rp_AcqSetTriggerSrc(acq_trig_sour)

# Trigger state
while 1:
    trig_state = rp.rp_AcqGetTriggerState()[1]
    if trig_state == rp.RP_TRIG_STATE_TRIGGERED:
        break

## ! OS 2.00 or higher only ! ##
# Fill state
while 1:
    if rp.rp_AcqGetBufferFillState()[1]:
        break


### Get data ###
# RAW
ibuff = rp.i16Buffer(N)
res = rp.rp_AcqGetOldestDataRaw(rp.RP_CH_1, N, ibuff.cast())

# Volts
fbuff = rp.fBuffer(N)
res = rp.rp_AcqGetDataV(rp.RP_CH_1, 0, N, fbuff)

data_V = np.zeros(N, dtype = float)
data_raw = np.zeros(N, dtype = int)

for i in range(0, N, 1):
    data_V[i] = fbuff[i]
    data_raw[i] = ibuff[i]

print(f"Data in Volts: {data_V}")
print(f"Raw data: {data_raw}")


# Release resources
rp.rp_Release()