Introduction of OSOYOO Universal IO Breakout Board

Fig 1 – OSOYOO Universal IO Breakout Board with an ESP32 module inserted

1. Overview

The OSOYOO Universal IO Breakout Board is a versatile GPIO expansion and debugging platform designed to accelerate hardware prototyping with virtually any MCU development board. Unlike fixed-format breakout boards that only work with one specific module, this board features two sets of 2×24P female pin-header sockets that accept MCU modules with a pin row spacing of 0.6 / 0.7 / 0.8 / 0.9 / 1.0 / 1.1 / 1.2 inch, making it compatible with Arduino Nano, ESP32 variants, ESP8266 NodeMCU, Raspberry Pi Pico, and many others. All pin headers use the standard 2.54 mm pitch.

A key feature is the per-pin LED status indicator: every GPIO pin on both socket sides has a dedicated LED that turns ON when the pin is driven HIGH and OFF when LOW. The LEDs are driven by an on-board 74LVC14AD hex Schmitt-trigger inverter, electrically isolated from the MCU GPIO — so the indicators add no load, do not affect ADC accuracy, and do not disturb open-drain buses (I²C, 1-Wire) or ESP32 strapping pins during boot.

Two on-board JW5357MSOTB#TR DC-DC step-down converters generate two fixed source voltages — one 5 V and one 3.3 V (up to 3 A each). The VCCA_Selector and VCCB_Selector jumpers then route the VA and VB rails to either the 3.3 V or the 5 V source, so each rail can be set independently to 3.3 V or 5 V — the two rails may be the same voltage or different. An SI2302 reverse-polarity protection MOSFET, on-board power switch, barrel-jack, and screw-terminal input complete the power system.

2. Target Applications

3. Features

• ✔ Universal MCU Compatibility — Two sets of 2×24P (48-pin) female sockets accept MCU boards with 0.6 / 0.7 / 0.8 / 0.9 / 1.0 / 1.1 / 1.2 inch pin-row spacing, covering most popular development boards.
• ✔ Per-Pin LED Status Indicators — Every GPIO pin on both socket sides has an individual LED reflecting real-time HIGH / LOW state. ON = HIGH, OFF = LOW.
• ✔ Non-Intrusive LED Drive Circuit — 74LVC14AD hex Schmitt-trigger inverters drive the LEDs, not MCU GPIO directly. Zero impact on GPIO load, ADC accuracy, I²C / SPI bus integrity, or boot strapping pins.
• ✔ Floating IO Warning — A floating (high-impedance) GPIO may partially illuminate its LED. This helps developers spot unconfigured pins at a glance.
• ✔ Reverse Polarity Protection — SI2302 N-channel MOSFET prevents damage when DC power polarity is accidentally reversed.
• ✔ Dual Selectable Power Rails (VA & VB) — Two on-board JW5357MSOTB#TR converters provide a fixed 5 V source and a fixed 3.3 V source (up to 3 A each). The VA and VB rails are independently routed to either source, so each can be 3.3 V or 5 V.
• ✔ Selectable Rail Voltage (3.3 V / 5 V) — VCCA_Selector and VCCB_Selector jumpers set each rail independently. Default: 3.3 V. Each rail must be set to one voltage only.
• ✔ Dual Peripheral Connection Options — Each GPIO row provides a 2.54 mm pin header and a screw terminal (S / V / G) for sensors, servos, and peripherals.
• ✔ Wide DC Input Range — 7–18 V DC via 5.5×2.1 mm barrel jack or screw terminal. Automatic DC / USB power switching on MCU power path.
• ✔ On-Board Power Switch — Slide switch enables / disables the VA / VB DC-DC outputs.
• ✔ USB Power Support — When using only MCU USB power, remove VA/VB Selector jumpers and connect VA/VB/GND correctly to prevent DC-DC backflow.

4. Technical Specifications

5. Board Layout & Components

5.1 Front View

Fig 2 – Front 2D PCB layout (A side left, B side right, power section bottom)

The board is divided into three zones:

• Left Zone (A side): MCU socket pins A1–A24, column order from outer to inner — S (signal header), V (VA power), A (MCU socket pin), G (GND). LED indicators sit adjacent to the A column.
• Right Zone (B side): MCU socket pins B1–B24, column order from inner to outer — G (GND), B (MCU socket pin), V (VB power), S (signal header). LED indicators sit adjacent to the B column.
• Bottom Zone (Power): Two DC-DC converters (one fixed 3.3 V, one fixed 5 V), ON/OFF switch, DC barrel jack, VIN screw terminal, VCCA_Selector jumper (bottom-left), VCCB_Selector jumper (bottom-right).

5.2 Back View & Silkscreen Notes

Fig 3 – Back 2D PCB layout showing usage reminders printed on silkscreen

Key reminders printed on the back silkscreen:

• “Floating IO may light LED!” — A floating GPIO may partially activate its LED. Always define pin modes in code.
• “USB Power: Remove VA/VB Selector, Connect VA/VB/GND Correctly” — When using only MCU USB power, remove the VCCA/VCCB Selector jumpers to prevent backflow into DC-DC converters.
• “7-18V DC Input” — DC barrel jack input range.
• “0.6–1.2″ Pitch Support” — MCU socket width compatibility range.
• “VA/VB Indep rails (Jumper for 3.3V/5V)” — VA and VB are fully independent; each has its own selector.
• “VA/VB: ONE VOLTAGE ONLY” — Each selector must bridge to either 3.3 V or 5 V, never both simultaneously.
• “Output 3A Max” — Maximum current per DC-DC converter output.

5.3 Component Descriptions

Fig 4 – PCB component layout render

6. Power Configuration

6.1 External DC Power (7–18 V) — Recommended for Full Operation

6.2 USB Power from MCU Board — LED Indicator Operation

When only USB power is available (e.g., connected to a computer for programming), the DC-DC converters are inactive. To power the LED indicators from the MCU’s USB supply:

6.3 VA / VB Rail Voltage Selection

7. Important Notes

• Floating GPIO Pins: An unconfigured (floating) GPIO may cause its LED to glow dimly or flicker. Always call pinMode(pin, OUTPUT) or pinMode(pin, INPUT_PULLUP) to define a stable state.
• MCU Power Pin Connection: Unlike fixed-format breakout boards, the MCU’s VCC and GND pin positions vary by board model. You must connect the MCU’s power pin(s) to the V and G rails manually (jumper cap or wire) before the MCU can receive power from the breakout board’s DC supply. See each MCU tutorial page for specifics.
• VA and VB Are Independent: A-side pins (A1–A24) are powered by VA; B-side pins (B1–B24) by VB. If all power pins are on one side, the other side’s V rail may have no power. Bridge between sides as needed.
• Maximum Input Voltage: Do not exceed 18 V on the VIN input. Higher voltage may damage DC-DC converters and other components.
• Minimum Input Voltage: A minimum of 7 V is required for correct DC-DC regulation. Input below 7 V results in unstable or incorrect output.
• Per-Converter Current Limit: The 3.3 V and 5 V sources are each rated 3 A. Because both rails draw from these two shared converters, if VA and VB are set to the same voltage their combined current must stay within that one converter’s 3 A; if set to different voltages each has its own 3 A.
• Confirm Voltage Before Connecting Peripherals: Applying 5 V to a 3.3 V-only sensor can permanently damage it. Verify the selector position first.
• LED Indicator Behavior:
  

  GPIO State	LED Indicator
  Output HIGH	LED ON (solid)
  Output LOW	LED OFF
  Floating / High-Z	LED may glow dimly or flicker
  Input with pull-up	LED ON
  Input with pull-down	LED OFF

8. Mechanical Information

Fig 5 – Back view showing PCB outline

9. Related Documents

MCU Tutorial Pages

ESP32
Arduino Nano
Raspberry Pi Pico
ESP8266 NodeMCU
Other Boards

OSOYOO Related Products

MCU Debug Shield Series
38P ESP32 Breakout
Nano Breakout Board
30P ESP8266 Breakout