Using the RS232 PAL with Arduino involves wiring up the breakout to your Arduino-compatible microcontroller with an external RS-232 device and running the provided example code.
Wiring
Wire as shown for a 5V board like an Uno. If you are using a 3V board, like an Adafruit Feather, wire the board's 3V pin to the breakout VIN.
Here is an Adafruit Metro wired up to the breakout with an external RS-232 connection:
- Metro 5V to breakout Vin (red wire)
- Metro GND to breakout GND (black wire)
- Metro pin 2 to breakout low voltage R1 (green wire)
- Metro pin 3 to breakout low voltage T1 (blue wire)
- Breakout high voltage R1 to RS-232 RXD [pin 2 on DE-9] (white wire)
- Breakout high voltage T1 to RS-232 TXD [pin 3 on DE-9] (yellow wire)
- Breakout GND to RS-232 GND [pin 5 on DE-9] (black wire)
Here is an Adafruit Metro wired up using a solderless breadboard:
- Metro 5V to breakout Vin (red wire)
- Metro GND to breakout GND (black wire)
- Metro pin 2 to breakout low voltage R1 (green wire)
- Metro pin 3 to breakout low voltage T1 (blue wire)
- Breakout high voltage R1 to RS-232 RXD [pin 2 on DE-9] (white wire)
- Breakout high voltage T1 to RS-232 TXD [pin 3 on DE-9] (yellow wire)
- Breakout GND to RS-232 GND [pin 5 on DE-9] (black wire)
There are no additional libraries needed for this example.
Example Code
You can change the baud rate for your RS-232 device at the top of the code by editing the baud define:
#define baud 38400
// SPDX-FileCopyrightText: 2024 Liz Clark for Adafruit Industries
//
// SPDX-License-Identifier: MIT
#include <SoftwareSerial.h>
// update this for your RS-232 device baud rate
#define baud 38400
// define RX and TX pins for the software serial port
#define RS232_RX_PIN 2
#define RS232_TX_PIN 3
SoftwareSerial rs232Serial(RS232_RX_PIN, RS232_TX_PIN);
void setup() {
Serial.begin(115200);
while ( !Serial ) delay(10);
rs232Serial.begin(baud);
Serial.println("Enter commands to send to the RS-232 device.");
Serial.println();
}
void loop() {
if (Serial.available() > 0) {
String userInput = Serial.readStringUntil('\n');
userInput.trim(); // remove any trailing newlines or spaces
if (userInput.length() > 0) {
// send the command with a telnet newline (CR + LF)
rs232Serial.print(userInput + "\r\n");
Serial.print("Sent: ");
Serial.println(userInput);
}
}
// check for incoming data from RS-232 device
while (rs232Serial.available() > 0) {
char response = rs232Serial.read();
// print the incoming data
Serial.print(response);
}
delay(50);
}
Upload the sketch to your board and open up the Serial Monitor (Tools -> Serial Monitor) at 115200 baud. You can send commands to your RS-232 device via the Serial Monitor. If any messages are received from the RS-232 device, they will print to the Serial Monitor.
The commands that you send will vary by the RS-232 device that you connect to the RS232 Pal. The output above was sent to a StarTech HDMI switcher. The AVI=n commands switch the selected HDMI port and the VS command gives a current status of the device.
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