This is a breakout/prototyping board for the ATMEGA328PB microcontroller which comes in the TQFP-32 format. It allows programming of the chip and breaks out all the pins to standard DuPont headers for project prototyping. My plan is to mount this PCB on a baseboard alongside a breadboard.
The microcontroller chip is placed in a TQFP-32 adapter, such as this one. These come with carrier boards to make the adapter fit standard DIP footprints. But my board doesn't use this - it just uses the main adapter itself which I have soldered into my PCB.
The pins for the four ports, B, C, D and E are gathered together logically (whereas they are somewhat scattered around on the microcontroller chip pinout itself).
- The AVCC pin is connected to VCC using a low-pass filter - ie, via a 10µH inductor with a 0.1µF capacitor to GND. This is Atmel's recommended setup which you want to use the analogue features of the microcontroller but don't want to go to the trouble of providing a separate analogue supply.
- There's a standard 6-pin header to connect an ISP programmer auch as the ATMEL-ICE.
- The ~RESET pin (PC6) has a pullup resistor and a tactile button to reset the microcontroller.
- The standard I2C pins (PC4, PC5) both have two additional pins for easy use of more than one I2C device. The additional pins are accompanied by +5V and GND pins. Onboard 10kΩ pullup resistors can be selected or deselected using jumpers.
- Female headers allow the use of an external crystal. This can be selected or deselected using jumpers. Onboard 22pF capacitors are connected between each leg of the crystal and GND.
- The standard UART pins – RX (PD0) and TX (PD1) have additional pins. These are in a row of six pins, including a GND connection, designed to match the normal order of connections on an FTDI USB-serial cable. Two of the other pins - RTS and CTS - are connected to two more pins. You can then use short female-female jumper cables to connect RTS and DTS to the GPIO pins of your choice.
- Finally, there are three lots of 4-pin connectors all tied to GND. Marked as 'test points', these are for the easy attachment of the GND clip for oscilloscope probes.
- There's an on-off slide switch for power. It is possible, however, that the board will be back-powered through any signals applied to the GPIO pins. Other than buffering every pin, I don't see any way to avoid this, so it's just something to watch out for.
- The power connector is a simple two-pin header. NO REVERSE POLARITY PROTECTION IS PROVIDED. Nor is there any over-voltage protection.
- The board is intended to be powered by 5V, although it might work on 3.3V (I haven't thought that through).
I've received the first batch of Rev 1.0 boards and have made up one, hand-soldered board. And, so far, it has worked flawlessly.