Button Debouncing Upgrade with SCPI Communication

This document introduces button debounce techniques combined with Red Pitaya SCPI control.

You’ll see how to:

Use UART (wired serial) or Wi-Fi to communicate with Red Pitaya

Combine hardware + software debounce for clean button inputs

Drive Red Pitaya’s onboard LED0 via SCPI

1) Prerequisites

Red Pitaya with SCPI server running

Start it from web UI (Development → SCPI → RUN)
Or via SSH:


systemctl start redpitaya_scpi

Arduino IDE 2.x installed

Library: ArduinoWifiXRedPitayaSCPI

Hardware:

Pushbutton
10 kΩ resistor (pull-down)
0.1 µF capacitor (RC hardware debounce)

2) UART Example (Button Debounce → LED0)

Wiring

Arduino TX → Red Pitaya RX

Arduino RX → Red Pitaya TX

Shared GND

Logic at 3.3 V

Button with pull-down resistor and capacitor for hardware debounce

Code



#include <Arduino.h>
#include "SCPI_RP.h"

#if defined(ARDUINO_ARCH_AVR)
#include <SoftwareSerial.h>
SoftwareSerial uart(8, 9);  // RX=8, TX=9 for UART SCPI
#endif

scpi_rp::SCPIRedPitaya rp;
uint8_t led_state = 1;

void setup() {
#if defined(ARDUINO_ARCH_AVR)
  uart.begin(RED_PITAYA_UART_RATE);
  rp.initStream(&uart);
#elif defined(ARDUINO_ARCH_ESP32) || defined(ARDUINO_ARCH_SAMD) || \
    defined(ARDUINO_ARCH_SAM)
  Serial1.begin(RED_PITAYA_UART_RATE);
  rp.initStream(&Serial1);
#endif
  rp.dio.reset();  // Reset all DIOs
}

void loop() {
  rp.dio.state((scpi_rp::EDIOPin)(led_state), 1);  // Turn LED on
  delay(1000);
  rp.dio.state((scpi_rp::EDIOPin)(led_state), 0);  // Turn LED off
  led_state++;
  if (led_state == 8) led_state = 0;               // Loop back
}

3) Wi-Fi Example (Button Debounce → LED0)

Setup arduino_secrets.h


#define SECRET_SSID    "YourWiFiSSID"
#define SECRET_PASS    "YourWiFiPassword"
#define SECRET_RP_IP   "192.168.1.42"   // or rp-xxxxxx.local
#define SECRET_RP_PORT 5025

Code


#include "wifiSCPI.h"
#include "arduino_secrets.h"     // WiFi + Red Pitaya settings

WifiSCPI rp;

const int buttonPin = 2;
int stableState      = HIGH;
int lastReading      = HIGH;
unsigned long lastDebounce = 0;
const unsigned long debounceDelay = 50;   // ms

void setup() {
  Serial.begin(115200);
  pinMode(buttonPin, INPUT_PULLUP);

  // Connect to Wi-Fi and Red Pitaya
  rp.begin(SECRET_SSID, SECRET_PASS, SECRET_RP_IP, SECRET_RP_PORT);

  // Configure LED0 as output
  rp.scpi("DIG:PIN:DIR LED0,OUT");
}

void loop() {
  int reading = digitalRead(buttonPin);

  if (reading != lastReading) {
    lastDebounce = millis();
  }

  if ((millis() - lastDebounce) > debounceDelay && reading != stableState) {
    stableState = reading;
    // LOW = button pressed
    rp.scpi(String("DIG:PIN LED0,") + (stableState == LOW ? "1" : "0"));
  }

  lastReading = reading;
}

4) Debounce Strategy

Hardware debounce:

10 kΩ pull-down resistor + 0.1 µF capacitor smooth out button bounce

Software debounce:

millis()based timer ensures only clean transitions are acted upon
Avoids blocking delays

5) Visual Verification

Use Red Pitaya’s Oscilloscope app to probe the button node:

Raw button signal (bouncy edges)

Hardware-debounced signal (smoother)

Final software-debounced toggling

This lets you compare real hardware vs. clean SCPI-driven LED toggling.

6) Troubleshooting

UART not working

Ensure correct TX/RX crossover and 3.3 V logic
Use Serial1 (hardware UART) where available; avoid high-baud SoftwareSerial

Wi-Fi connection fails

Verify SSID/password in arduino_secrets.h
Test Red Pitaya IP with ping

LED0 does not toggle

Confirm SCPI server is running (systemctl status redpitaya_scpi)
Try port 5025 or 5000 depending on OS version

Oscilloscope app + SCPI conflicts

Avoid running heavy web apps while using SCPI (they share FPGA/DSP resources)