SparkFun RS232 Breakout

The SparkFun RS232 Breakout is a simple and essential utility board for interfacing modern electronics with legacy RS232 serial devices. If you've ever needed to connect your 3.3V microcontroller to an older computer, industrial machine, GPS module, or any other device that uses a DE9 (also known as DB9) connector, this board is the solution. It perfectly bridges the gap between low-voltage TTL logic and the higher-voltage RS232 standard.

The Logic Level Bridge

At its core, the breakout features the ST3222 RS232 driver/transceiver from STMicroelectronics, which handles the task of voltage-level shifting, converting your microcontroller's 3.3V logic signals into the ±5V (or higher) signals required by RS232, and vice versa.

The board operates at a low power supply voltage of 3.0V to 3.6V, making it a perfect match for any 3.3V microcontroller. It reliably supports data rates of up to 250Kbps, more than enough for most RS232 applications. For battery-powered projects, the ST3222 also features a low-power shutdown mode that drops the supply current to just 1mA, allowing it to monitor for device activity.

Simple, No-Hassle Connections

We designed this board for simplicity. The female DE9 connector allows you to plug in your RS232 device cable directly. For your microcontroller, all the necessary pins are broken out to a standard 0.1"-spaced, 9-pin plated through-hole (PTH) header.

A key feature of this board is that it handles the TX/RX signal crossover internally. You no longer need to guess if you need a null-modem or crossover cable. Simply connect your microcontroller's TX pin to the TX pin on the breakout and the RX pin to the RX pin. The board takes care of the rest, simplifying your wiring and troubleshooting. Two mounting holes are also included for securing the board into an enclosure or project.

• Schematic
• KiCad Files
• Datasheet (ST3222)
• GitHub Repository