3.2.9. RF Signal Recording and Playback script

RF Signal Record and Playback script captures RF signal pulses from Red Pitaya’s analog inputs (IN1/IN2) and immediately replays them on the corresponding outputs (OUT1/OUT2). It leverages Deep Memory Acquisition for high-speed recording and Deep Memory Generation for precise playback.

Once installed, the application is set to start automatically at boot. The application is controlled through the configuration file located in the /opt/redpitaya/bin/ directory.

How it works

Acquisition: Each channel independently monitors its input for trigger conditions
Recording: When triggered, captures the signal using DMA for minimal latency
Generation: Immediately replays the captured signal with configurable burst patterns
Loop: Continues indefinitely until stopped

Features

Dual Channel Processing: Independent IN1→OUT1 and IN2→OUT2 signal recording/playback
Deep Memory Mode: High-speed acquisition using Red Pitaya’s DMA capabilities
Split Trigger Mode: Isolated trigger handling for each channel
Configurable Parameters: Flexible trigger levels, buffer sizes, and burst patterns
Real-time Operation: Low-latency signal processing with threaded architecture
Auto-start: Automatic startup on Red Pitaya boot

Note

This application is not meant to be used in parallel with the Red Pitaya WEB interface. As most processing resources is taken by the Record and Play application, the Web interface is severly slowed down.

Requirements

Hardware

Any Red Pitaya device
Properly terminated analog inputs/outputs (50 Ω impedance matching)

Software

Red Pitaya Linux 2.07 or higher
Nightly Build 637 or higher

Warning

This application consumes significant system resources and cannot run simultaneously with the Red Pitaya Web Interface. The web interface will be severely slowed down or unresponsive.

Please make sure that Red Pitaya inputs and outputs are properly terminated (matched impedance). Failure to do so may lead to undefined behaviour of the Record and Playback application due to the ringing on the transmission line. Red Pitaya fast analog inputs have input impedance of 1 MΩ. The fast analog outputs have output impedance of 50 Ω.

Installation

Quick Start

Connect to your Red Pitaya via SSH
Clone the repository: git clone https://github.com/RedPitaya/rec_and_play.git
Enable running scripts: chmod +x ./rec_and_play/setup.sh
Run setup: cd rec_and_play && ./setup.sh
Reboot Red Pitaya
Done! Application starts automatically on boot

Option A: Automatic Setup (Recommended)

Establish SSH connection with your Red Pitaya

Download the rec_and_play GitHub Repository to the Red Pitaya.

cd /root
git clone https://github.com/RedPitaya/rec_and_play.git rap
cd rap

Make sure all the scripts are executable and run the setup.
```
chmod +x setup.sh
./setup.sh
```
Reboot Red Pitaya.
```
reboot
```

Option B: Manual Setup

Establish SSH connection with your Red Pitaya
Download the rec_and_play GitHub Repository to the Red Pitaya.
```
cd /root
git clone https://github.com/RedPitaya/rec_and_play.git rap
```
Alternatively, download the repository to your computer and copy the code to the Red Pitaya through the SCP command:
```
scp -r /<path-to-downloaded-repository>/rec_and_play root@rp-xxxxxx.local:/root
```
Move to the Record and Play directory on the Red Pitaya.
```
cd /root/rap
```

Enter read-write mode and copy the scripts into the /opt/redpitaya/bin folder.

rw
cp -f ./main.py /opt/redpitaya/bin/
cp -f ./config.ini /opt/redpitaya/bin/

(Optional) Add to startup by editing /opt/redpitaya/sbin/startup.sh and adding:

export PYTHONPATH=/opt/redpitaya/lib/python/:$PYTHONPATH
/opt/redpitaya/bin/main.py

Reboot Red Pitaya.
```
reboot
```

Configuration

The Record and Play application uses the configuration file (config.ini) located in /opt/redpitaya/bin/ directory. Each channel (ADC/DAC) is configured independently.

Acquisition Settings (ADC)

Parameter	Description	Values	Unit
trigger_level	Voltage threshold for triggering	-1.0 to 1.0	Volts
trigger_mode	Trigger condition	CH1_PE, CH1_NE, CH2_PE, CH2_NE	-
buffer_time	Recording duration	1-30	µs

Generation Settings (DAC)

Parameter	Description	Values	Unit
signal_source	Input channel to record	IN1, IN2	-
count_burst	Cycles per burst (NCYC)	≥1	count
repetition	Number of bursts (NOR)	≥1	count
repetition_delay	Delay between bursts	≥ (buffer_time × count_burst + 1)	µs

Sample Configuration

To change the settings, either edit the config.ini file in /opt/redpitaya/bin/ directly, or edit the config.ini file in the record and play directory and run the setup.sh script again. For the changes to take effect, main.py must be restarted (either by rebooting the Red Pitaya or by killing the process and starting it again).

Example of “config.ini”:

[ADC1]
; IN1 Trigger Level in volts
trigger_level=0.1
; Trigger source (Values: CH1_PE, CH1_NE)
trigger_mode=CH1_PE
; Record signal Buffer size in microseconds (min 1 µs)
buffer_time=20

[ADC2]
; IN2 Trigger Level in volts
trigger_level=0.1
; Trigger source (Values: CH2_PE, CH2_NE)
trigger_mode=CH2_PE
; Record signal Buffer size in microseconds (min 1 µs)
buffer_time=20

[DAC1]
; OUT1 Gen signal from source (IN1, IN2). Which input to use for recording data.
signal_source=IN1
; Number of signal repetitions without delays (NCYC - number of cycles/periods in a single burst).
count_burst=1
; Number of repetitions with delay (NOR - Number of Repetitions/Bursts). Each repetition includes `count_burst` (NCYC) recordings without delay.
repetition=3
; Delay between repetitions.
; If there is a "repetition" number of repetitions, then the minimum allowed delay must be no less than:
; buffer_time * count_burst + 1 µS
; Otherwise the signal may break. If there are no repetitions, the value is ignored
; For example. buffer_time = 20, count_burst=2. repetition_delay = 20 * 2 + 1 = 41 µS
repetition_delay=50

[DAC2]
; OUT2 Gen signal from source (IN1, IN2). Which input to use for recording data.
signal_source=IN2
; Number of signal repetitions without delays (NCYC - number of cycles/periods in a single burst).
count_burst=1
; Number of repetitions with delay (NOR - Number of Repetitions/Bursts). Each repetition includes `count_burst` (NCYC) recordings without delay.
repetition=3
; Delay between repetitions.
; If there is a "repetition" number of repetitions, then the minimum allowed delay must be no less than:
; buffer_time * count_burst + 1 µS
; Otherwise the signal may break. If there are no repetitions, the value is ignored
; For example. buffer_time = 20, count_burst=2. repetition_delay = 20 * 2 + 1 = 41 µS
repetition_delay=50

Note

Cross-channel routing is supported but untested (e.g., IN1 to OUT2)
Buffer sizes should be identical for both channels
Timing constraints must be respected to avoid signal corruption

Usage

Starting the Application

The application starts automatically on boot if installed with setup.sh. For manual start:

cd /opt/redpitaya/bin
python3 main.py

Monitoring Operation

Check system logs for status messages
Use top or htop to monitor CPU usage
Application runs indefinitely until interrupted

Stopping the Application

Temporary Stop - To stop the application until the next boot:

Press Ctrl+C in the terminal, or
Kill the process in top (write k and the PID of the process)

Permanent Disable - First stop the application, then:

Remove it from the startup.sh script located in /opt/redpitaya/sbin directory (you may have to enter rw mode).

Either delete or comment the following lines of code:

# Here you can specify commands for autorun at system startup
export PYTHONPATH=/opt/redpitaya/lib/python/:$PYTHONPATH
/opt/redpitaya/bin/main.py

You can also remove the main.py and config.ini from /opt/redpitaya/bin.

Troubleshooting

Common Issues

Error setting split trigger

Ensure you’re using compatible Red Pitaya OS version
Check that system resources aren’t exhausted

Invalid buffer size

Verify buffer_time is between 1-30 µs
Ensure integer values in configuration

No signal output

Check input signal levels and trigger settings
Verify proper impedance termination (50 Ω)
Confirm signal_source configuration

System slowdown

This is normal - application uses most system resources
Web interface will be unresponsive during operation

Performance Tuning

Reduce buffer_time for faster response
Adjust repetition_delay to prevent signal overlap
Monitor CPU usage with top command
Reduce the value of LOOP_DELAY to achieve faster trigger checking

FAQ

Q: Can I use this with the Web Interface?

A: No, this application consumes all processing resources and will make the web interface unresponsive.

Q: What’s the maximum buffer size?

A: 30 µs maximum, limited by Red Pitaya’s DMA capabilities.

Q: Can I route IN1 to OUT2?

A: Yes, but this configuration is untested. Use signal_source=IN1 in DAC2 section.

Q: How do I change trigger sensitivity?

A: Adjust trigger_level in ADC sections (range: -1.0 to 1.0 Volts).

Q: Why does the signal break up?

A: Usually due to insufficient repetition_delay. Ensure it’s ≥ (buffer_time × count_burst + 1) µs.

Source code

The Playback and Record source code is available on our GitHub.