Mini Version Of The Arduino Uno
Reviewed by: Morgan Winters - 06 April 2018
I picked up one of these for a user interface for a pet cage. I'd already another one I bought from somewhere else but it is a 5V 16MHz version. I needed the 3.3V version as the UI uses serial connection to a Raspberry Pi, I didn't want to use a level shifter for the different logic voltages. For my use and indeed, most project, the difference between the 12MHz and 16MHz is not noticeable so don't let the different clock speeds put you off getting the 3.3V version.
Regardless, Adafruit did a great job designing this, it a rugged little device and uses very little power (9mA running Arduino's blink example (according to my bench power supply)). When I said little, the ProTrinket is only 38mm long by 18mm wide and 2mm high, excluding header pins. These header pins come with the ProTrinket but are not soldered to the board, you'll need to solder them on yourself, if you choose to use them.
The ProTrinket is basically a mini Arduino Uno, it uses the same Atmel Atmega 328P chip, you get 32Kb of storage space, 28672 bytes once you take into account the bootloader and you get 2Kb of RAM. Once you make few simple config modifications, you can use the Arduino IDE to program your sketch and the ProTrinket can run pretty much run any Arduino Uno sketch. You get 6 PWM pins which can be used as PWM outputs or digital inputs or output plus 4 more digital input/output pins, 8 analogue input pins with a analogue reference pin, A4 and A5 can used as analogue inputs or for bi-directional I2C, you also get 2 serial UART pins. You can power the device through the USB connector or through the BAT pin. There is a voltage regulator onboard so you can power the ProTrinket with upto 16VDC. The voltage regulator can output upto around 150mA and if needed, you can power other things from the 3V or 5V pins, depending on version.
Please note, unlike the full size Arduino Uno, the ProTrinket does not have an Atmega16U2 chip for the USB. Adafruit have made pins 2 and 7 unavailable and are used exclusively for USB, The Atmega16U2 chip has been done away with and the device uses a modified bootloader, as a result, one can only upload new sketches for a limited time when the device starts up. Pin 13 has a LED attached, while this is pulsing, you can upload new code. There is an onboard reset button to restart the device,it will then re-enter the sketch upload halt period.
Also note that there is no serial via USB so you cannot use the ProTrinket to make a keyboard/mouse/gamepad type USB controller. The USB is only for uploading new code at startup and for powering the device, nothing else. The UART serial pins have been broken out and serial communication is still possible through the RX/TX pins, you just can't use the USB for serial or use the Serial Monitor with the Arduino IDE. You can use the FTDI port if you have a cable but I have never used FTDI nor know how it works so I can't offer any review on that.
All in all, if you don't need serial through USB, the ProTrinket is a great low cost alternative to the Arduino Uno but in a far smaller package. Ideal for those projects where the capability of the Arduino Uno is needed but size and power is limited. A great little device, well made by Adafruit and topped off with perfect service yet again from Rapid Electronics.