Retronics

For breadboarding/prototyping small microcontroller circuits, the Arduino Pro Mini may be a good choice. One annoying thing about this board is that pins A4-A7 aren’t placed along with the other pins, and hence not available directly to the breadboard.

The Pro Mini has an onboard voltage regulator which can handle up to 16V input voltage and 150mA current draw, but not simultaneously, because the tiny SOT23-5 package has a thermal resistance (θ_JA) of 220°C/W, and would quickly overheat.

---

I decided to make my own mini “Arduino” board, with all pins available along the sides of the board, and with an integrated switching voltage regulator for powering peripherals.

The switched voltage regulator is based on TPS54302 from Texas Instruments, which accepts up to 28V input voltage, and can deliver up to 3A (if accompanied by an inductor which can handle this current). To save space, a smaller inductor is used in this case: a TDK VLS252012HBX-100M-1 which has saturation current of 1A and max DC current of 850mA. To be on the safe side, let’s say max output current is 500mA (which is plenty for driving peripherals like displays and sensors).

The regulator circuit is followed by a Reverse current protection circuit, to ensure that the voltage regulator doesn’t interfere with (draw current from) any 5V supply that is connected to the +5V pin.

The rest of the circuit is pretty much like the Arduino Pro Mini, except I’ve added pull-up resistors for I²C, and indicator LEDs for both unregulated input voltage (Vin) and regulated +5V.

If you want to make this board yourself, I’ve shared KiCad design documents and Gerber files on Github: https://github.com/donpivo/ATMEGA328P/tree/main/ATMEGA328P_AU_BreadboardAdapter/Schematic

In addition to the 5V version running at 16MHz, I made a 3.3V version running at 8MHz.

Note: I recommend burning bootloader to the ATMEGA328P-AU before soldering. This can be done using a Bootloader Burner.

The 3.3V and 5V pins can be used as either power input (regulated DC in), or power output (to drive peripherals like displays or sensors), but must never be subject to higher voltages than 3.3V or 5V respectively.