Arduino Pro Mini

The Arduino Pro Mini is a compact microcontroller board for advanced users, based on ATmega168 or ATmega328P. Designed for space-constrained projects, it lacks a USB port, requiring an external FTDI programmer for coding. Operating at 3.3V or 5V, it offers 14 digital I/O pins, 6 analog inputs, and 32KB flash memory. Lightweight and versatile, it’s ideal for embedded systems and permanent installations.

Features/Specifications

• Operating Voltage: There are 5V and 3.3V models. With the latter, care must be taken to ensure that a voltage higher than 3.3V is never applied, not even during programming.
• Programming: The Pro Mini does not have a USB interface like the Arduino Uno and therefore must be programmed using a separate USB-to-Serial adapter (in this case, the Arduino Uno board itself is used).
• Microcontroller: Pro Mini models are available with either the ATmega168P or the ATmega328. (Each with either 8MHz or 16MHz clock frequency)

Older boards were equipped with ATmega 168 with this specs:

• Flash memory: 16 KB
• SRAM: 1 KB
• EEPROM: 512 bytes

📄 ATMega328P datasheet (8585 kB)
📄 Arduino Pro Mini schematic (61 kB)

Connections

Used Components

Programming

There are various ways to program the Pro Mini. Programming via USB directly from a PC is not possible, as it does not have its own USB interface. You can connect the Pro Mini to a PC using an FTDI adapter (similar to the Lilypad), use the Arduino Uno as an ISP (Caution: 3.3V!), or use the Arduino Uno board directly as a programmer, as described below.

Preparation

First, the ATMega328 chip must be carefully removed from the Arduino Uno board. This can be done easily by gently prying it out with a screwdriver (see the image below).

Connections

Now the Pro Mini is connected to the Arduino board as follows:

In the Arduino IDE, go to "Tools → Board:" and select "Arduino Pro Mini", then choose the appropriate chip, voltage, and port. The Pro Mini can now be programmed as usual.

Test-Program

As a small test, a slightly modified version of the Blink sketch is used here.

void setup() {
    pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
    digitalWrite(LED_BUILTIN, HIGH);
    delay(200);
    digitalWrite(LED_BUILTIN, LOW);
   delay(1500);
}

Power saving

In the following experiment, we want to measure how much power the Arduino Pro Mini consumes in so-called sleep mode. This is especially important for battery-powered projects, where the goal is to achieve the longest possible battery/runtime.
The circuit setup is quite simple: a standard LED with a current-limiting resistor is connected to one of the pins (here: pin 13). The following sketch turns the LED on for 4 seconds, then off for 4 seconds, and then puts the board into sleep mode for 4 seconds. A 18650 Li-Ion battery with a battery board (3V output) is used as the power source. (This uses the LowPower library, which must be installed before compiling the sketch.)

#include "LowPower.h"

void setup() {
    pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
    digitalWrite(LED_BUILTIN, HIGH);
    delay(4000);
    digitalWrite(LED_BUILTIN, LOW);
    delay(4000);
    LowPower.idle(SLEEP_4S, ADC_OFF, TIMER2_OFF, TIMER1_OFF, TIMER0_OFF, SPI_OFF, USART0_OFF, TWI_OFF);
}

The measured current in the three different phases is as follows:

For even greater power savings, the red power LED and the voltage regulator can also be removed. However, this requires a modification to the board itself, which is described, for example, on Andreas Rohner's website.