Adafruit sure love the ATmega328 here at Adafruit, and Adafruit use them a lot for Adafruit's own projects. The processor has plenty of GPIO, Analog inputs, hardware UART SPI and I2C, timers and PWM galore - just enough for most simple projects. When Adafruit need to go small, Adafruit use a Pro Trinket 3V or 5V, but when size isn't as much of a concern, and an USB-serial converter is required, Adafruit reach for an Adafruit METRO.
This is the Adafruit METRO with headers. It comes with headers soldered on. It's a fully assembled and tested board with SMT headers attached as well as through hole headers. If you don't want a Metro with through-hole headers or at least, holes for them, but not attached for super-slimness, check out Adafruit's Metro without Headers.
METRO is the culmination of years of playing with AVRs: Adafruit wanted to make a development board that is easy to use and is hacker friendly. At the heart is an ATmega328P, with 32KB of flash and 2KB of RAM, running at 16 MHz
- Power the METRO with 7-9V polarity protected DC or the micro USB connector to any 5V USB source. The 2.1mm DC jack has an on/off switch next to it so you can turn off your setup easily. The METRO will automagically switch between USB and DC.
- METRO has 19 GPIO pins, 6 of which are Analog in as well, and 2 of which are reserved for the USB-serial converter. There's also 6 PWMs available on 3 timers (1 x 16-bit, 2 x 8-bit). There's a hardware SPI port, hardware I2C port and hardware UART to USB. Logic level is 5V but by cutting and soldering closed a jumper, you can easily convert it to 3.3V logic
- USB to Serial converter, there's a hardware USB to Serial converter that can be used by any computer to listen/send data to the METRO, and can also be used to launch and update code via the bootloader
- Four indicator LEDs, on the front edge of the PCB, for easy debugging. One green power LED, two RX/TX LEDs for the UART, and a red LED connected to pin PB5
- Easy reprogramming, comes pre-loaded with the Optiboot bootloader, which is supported by avrdude and only uses 512 bytes.
- Works with all Adafruit shields!
They also include 4 rubber bumpers to keep it from slipping off your desk. Metro shown with Adafruit's 12x capacitive touch shield attached just to demonstrate the headers, but that shield is not included!
- ATmega328 microcontroller with Optiboot (UNO) Bootloader
- USB Programming and debugging via the well-supported genuine FTDI FT231X
- Input voltage: 7-9V (a 9VDC power supply is recommended)
- 5V regulator can supply peak ~800mA as long as the die temp of the regulator does not exceed 150*C
- 3.3V regulator can supply peak ~150mA as long as the die temp of the regulator does not exceed 150*C
- 5V logic with 3.3V compatible inputs, can be converted to 3.3V logic operation
- 20 Digital I/O Pins: 6 are also PWM outputs and 6 are also Analog Inputs
- 6-pin ICSP Header for reprogramming
- 32KB Flash Memory - 0.5K for bootloader, 31.5KB available after bootloading
- 16MHz Clock Speed
- Compatible with "Classic" and "R3" Shields
- Adafruit Black PCB with gold plate on pads
- 53mm x 71mm / 2.1" x 2.8"
- Height (w/ barrel jack): 13mm / 0.5"
- Weight: 19g
- Derivative of "Arduino UNO R3 Reference design"
- Open source hardware files on github!
- As of August 31, 2015 Adafruit have updated the Metro's headers to be slightly taller so that they are the same height as classic 'non-SMT' headers for a better shield-fit
Documentation and Resources:
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