The SparkFun RS232 Breakout converts 3.3V TTL serial to RS232 via a DE9 connector using the ST3222 transceiver, supporting up to 250 kbps and handling TX/RX crossover on-board for easy, reliable legacy serial connections.
The SparkFun RS232 Breakout is a simple utility board for connecting modern 3.3V electronics to devices that still use the RS232 serial standard. It’s ideal when you need to interface a 3.3V microcontroller with older computers, industrial equipment, GPS modules, or anything using a DE9 (DB9) connector. The board acts as a bridge between low-voltage TTL serial signals and the higher-voltage RS232 signalling used by legacy hardware.
At the heart of the breakout is the ST3222 RS232 driver/transceiver from STMicroelectronics. This handles the voltage-level shifting in both directions, converting 3.3V logic into the ±5V (or higher) signals required by RS232, and translating incoming RS232 signals back to logic-level serial for your microcontroller.
The board is designed to run from 3.0V to 3.6V, making it a good match for typical 3.3V systems. It supports data rates up to 250 kbps, which is more than enough for most RS232 applications. For low-power projects, the ST3222 also includes a shutdown mode that reduces supply current to 1 mA, while still allowing it to monitor for activity.
Connection is kept straightforward. A female DE9 connector lets you plug an RS232 cable directly into the board, and all required signals are broken out to a 0.1" (2.54 mm) spaced 9-pin plated through-hole header for easy wiring to your microcontroller. The board also handles TX/RX crossover internally, so you don’t need to worry about whether you need a null-modem cable — just connect TX to TX and RX to RX. Two mounting holes are included for securing the board in an enclosure or project.
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