Function generator

Guide to Using Red Pitaya: Function Generator

Overview:

A function generator creates a variety of electrical waveforms, such as sine waves, square waves, and triangle waves. These signals are essential for testing and simulating real-world scenarios in circuits. In this guide, we’ll cover the basics of using Red Pitaya’s Function Generator, focusing on creating and controlling waveforms to complement your Arduino projects.

Objectives:

1. Understand the purpose of a function generator and its role in electronics testing.
2. Learn how to set up and use Red Pitaya’s Function Generator to create signals.
3. Perform practical experiments to observe the behavior of generated signals in Arduino-controlled circuits.

What is a Function Generator?

• A device that generates various types of waveforms at different frequencies, amplitudes, and offsets.
• Commonly used to test:
• Circuit response to specific signals (e.g., filters, amplifiers).
• Behavior of microcontrollers under simulated conditions.

Setup and Connections:

Hardware Requirements:

1. Red Pitaya STEMlab 125-14
2. Arduino Uno (Optional): For testing how the generated signal interacts with microcontroller-based systems.
3. Oscilloscope (Optional): To visualize the output signal (can use Red Pitaya’s built-in oscilloscope).
4. Probes and Wires: For signal connections.

Connections:

1. Red Pitaya Outputs:
• Connect OUT1 or OUT2 to the input of your test circuit (e.g., Arduino analog pin or breadboard).
2. Red Pitaya Inputs (Optional):
• To observe the generated signal, loop back OUT1 to IN1.
3. Common GND:
• Ensure Red Pitaya and the connected circuit (e.g., Arduino) share a common ground.

Step-by-Step Instructions:

1. Accessing the Function Generator:

1. Open a web browser and navigate to http://<Red_Pitaya_IP>.
2. Select Oscilloscope & Signal Generator from the application menu.

2. Configuring the Function Generator:

1. Select the Output Channel:
• Choose OUT1 or OUT2 for signal generation.
2. Choose the Waveform Type:
• Options include:
• Sine
• Square
• Triangle
• Sawtooth
3. Set Parameters:
• Frequency: Controls how fast the waveform repeats (e.g., 1 kHz).
• Amplitude: Controls the peak-to-peak voltage of the waveform (e.g., 1 Vpp).
• Offset: Adjusts the DC level of the waveform (e.g., centered around 0 V or shifted to 2 V).

3. Example: Generating a 1 kHz Sine Wave

1. Select OUT1 and set the waveform to Sine.
2. Configure:
• Frequency: 1 kHz.
• Amplitude: 2 Vpp.
• Offset: 0 V.
3. Connect OUT1 to a circuit or IN1 for visualization.
4. Observe the waveform on Red Pitaya’s oscilloscope.

4. Practical Exercises:

1. Simulate a PWM Signal:
• Generate a 500 Hz square wave with 50% duty cycle.
• Connect OUT1 to Arduino digital input and write a sketch to detect the high/low states:
Copy

const int inputPin = 2;

void setup() {
    pinMode(inputPin, INPUT);
    Serial.begin(9600);
}

void loop() {
    int state = digitalRead(inputPin);
    Serial.println(state);
    delay(100);
}

2. Drive an LED:
• Use a 1 kHz sine wave to vary LED brightness.
• Connect OUT1 through a 220 Ω resistor to the LED.
• Adjust amplitude and observe changes in brightness.
3. Test Arduino AnalogRead Function:
• Generate a triangle wave (0–5 V) and connect OUT1 to an Arduino analog pin:
Copy

const int analogPin = A0;

void setup() {
    Serial.begin(9600);
}

void loop() {
    int value = analogRead(analogPin);
    Serial.println(value);
    delay(100);
}

• Observe the analog values varying in response to the triangle wave.

Advanced Usage:

1. Sweeping Signals:

• Use the sweep feature to gradually change the frequency of the waveform.
• Example: Test a filter circuit by sweeping from 1 Hz to 10 kHz and observe its response.

2. Custom Waveforms:

• Upload a custom waveform:
• Use a Python script or the Red Pitaya web interface to define a custom signal.
• Example Python code to generate a custom waveform:
Copy

import numpy as np
import redpitaya_scpi as scpi

rp = scpi.scpi("192.168.1.100")
wave = np.sin(np.linspace(0, 2 * np.pi, 16384))  # Sine wave
rp.tx_txt("SOUR1:DATA:VOLTS " + ",".join(map(str, wave)))
rp.tx_txt("OUTPUT1:STATE ON")

Common Adjustments:

1. Amplitude Clipping:
• Ensure the amplitude does not exceed the maximum input range of connected devices.
2. DC Offset:
• Adjust offset to shift the signal as needed for compatibility with the circuit.

Real-World Applications:

• Testing sensors and actuators by simulating environmental signals.
• Debugging and validating circuit designs.
• Generating control signals for industrial or laboratory systems.

Summary:

• What You Learned:
• How to use Red Pitaya’s Function Generator to create various waveforms.
• How to configure parameters like frequency, amplitude, and offset.
• How to test generated signals in real-world scenarios.
• Next Steps:
• Combine the Function Generator with the Oscilloscope for signal analysis.
• Move on to the Spectrum Analyzer to explore frequency-domain analysis.