2.2.4.3.2. Signal acquisition on external trigger

2.2.4.3.2.1. Description

This example shows how to acquire 16k samples of signal on fast analog inputs. Signal will be acquired when the external trigger condition is meet. Time length of the acquired signal depends on the time scale of a buffer that can be set with a decimation factor. Decimations and time scales of a buffer are given in the table below. Voltage range of fast analog inputs on the Red Pitaya depends on gain setting that can be set by jumpers. HV setting is for input range to ±20V, while LV sets input range to ±1V.

Decimation Sampling Rate Time scale/length of a buffer Trigger delay in samples Trigger delay in seconds
1 125 MS/s 131.072 us from - 8192 to x -6.554E-5 to x
8 15.6 MS/s 1.049 ms from - 8192 to x -5.243E-4 to x
64 1.9 MS/s 8.389 ms from - 8192 to x -4.194E-3 to x
1024 122.0 MS/s 134.218 ms from - 8192 to x -6.711E-2 to x
8192 15.2 kS/s 1.074 s from - 8192 to x -5.369E-1 to x
65536 7.6 kS/s 8.590 s from - 8192 to x -4.295E+0 to x

2.2.4.3.2.2. Required hardware

  • Red Pitaya
  • Signal (function) generator
../../../_images/on_given_external_trigger_acquire_signal_on_fast_analog_input.png

2.2.4.3.2.3. Circuit

../../../_images/on_given_external_trigger_acquire_signal_on_fast_analog_input_circuit.png

2.2.4.3.2.4. Code - MATLAB®

The code is written in MATLAB. In the code we use SCPI commands and TCP/IP communication. Copy code to MATLAB editor
and press run.

%% Define Red Pitaya as TCP/IP object
clear all
close all
clc
IP= '192.168.178.111';                % Input IP of your Red Pitaya...
port = 5000;
tcpipObj = tcpip(IP, port);
tcpipObj.InputBufferSize = 16384*32;

%% Open connection with your Red Pitaya

fopen(tcpipObj);
tcpipObj.Terminator = 'CR/LF';

flushinput(tcpipObj);
flushoutput(tcpipObj);

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

fprintf(tcpipObj,'ACQ:RST');
fprintf(tcpipObj,'ACQ:DEC 1');
fprintf(tcpipObj,'ACQ:TRIG:LEV 0');

% Set trigger delay to 0 samples
% 0 samples delay set trigger to center of the buffer
% Signal on your graph will have trigger in the center (symmetrical)
% Samples from left to the center are samples before trigger
% Samples from center to the right are samples after trigger

fprintf(tcpipObj,'ACQ:TRIG:DLY 0');

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

fprintf(tcpipObj,'ACQ:START');
% After acquisition is started some time delay is needed in order to acquire fresh samples in to buffer
% Here we have used time delay of one second but you can calculate exact value taking in to account buffer
% length and smaling rate
pause(1)

fprintf(tcpipObj,'ACQ:TRIG EXT_PE');
% Wait for trigger
% Until trigger is true wait with acquiring
% Be aware of while loop if trigger is not achieved
% Ctrl+C will stop code executing in Matlab

while 1
    trig_rsp=query(tcpipObj,'ACQ:TRIG:STAT?')

    if strcmp('TD',trig_rsp(1:2))  % Read only TD

    break

    end
end


% Read data from buffer
signal_str=query(tcpipObj,'ACQ:SOUR1:DATA?');
signal_str_2=query(tcpipObj,'ACQ:SOUR2:DATA?');

% Convert values to numbers.% First character in string is “{“
% and 2 latest are empty spaces and last is “}”.

signal_num=str2num(signal_str(1,2:length(signal_str)-3));
signal_num_2=str2num(signal_str_2(1,2:length(signal_str_2)-3));

plot(signal_num)
hold on
plot(signal_num_2,'r')
grid on
ylabel('Voltage / V')
xlabel('samples')

fclose(tcpipObj)

2.2.4.3.2.5. Code - Python

#!/usr/bin/python

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

rp_s = scpi.scpi(sys.argv[1])

rp_s.tx_txt('ACQ:DEC 8')
rp_s.tx_txt('ACQ:TRIG:LEVEL 100')
rp_s.tx_txt('ACQ:START')
rp_s.tx_txt('ACQ:TRIG EXT_PE')

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

rp_s.tx_txt('ACQ:SOUR1:DATA?')
buff_string = rp_s.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()
view rawacquire_trigger_external.py

2.2.4.3.2.6. Code - LabVIEW

../../../_images/Signal-acquisition-on-external-trigger_LV.png

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