I have bought a few Atmega328PB TQFP to use the double I2C channel and now I am searching for a PCB design to make a breakout board for them. They have only a few different pins compared to the Atmega328P.
I then want to get rid of the reset button and add a 6 pin ISP header instead (I don't use bootloader).
The Uino looked like a good design, but no design files exist.
I decided to take the reference NANO design and make some changes to accommodate my requirements. The board is just 2 pins longer on the left side to deal with the extra E0 and E1 pins. For the rest I did not change pins, so it is still Nano shield compatible. Except for the 3.3V pin, that I leave empty.
I wanted the big type of crystal, 0805 size capacitors, a AMS1117 regulator and no parts on the bottom so I can solder everything very easy by hand .
After testing a first prototype I made some changes to come to a better version
Added 2 pro-mini style serial programming headers. That way I can hook up two serial adapters. and if needed use a bootloader on either of them as Minicore supports a bootloader for both UARTs.
added the led on Pin 13
added a external pullup for reset, in case the internal 50K pullup is not sufficient.
This one is for breadboard duty, so I may not even solder the AMS1117 on it, as my breadboards have 5V already. It's for "just in case" when e.g. I want to solder it as a prototype somewhere in a car or motorcycle that has 12V. So for the why question, it's because this was a solution where I can do with a crappy regulator that is easy to solder by hand and I have too many from laying in the drawer.
If it needs to be battery operated I usually design without regulator for 3 Alkaline cells or a 1 cell lithium.
If I need less dropout, I tend to grab a HT7350 (that won't meet the MCP1702 sleep current though).
Oh, and same for the crystal. The 328PB has a 2% internal oscillator compared to the 10% of the 328P (both without extra calibration). So I may not need the crystal often and need to figure out the proper value of the capacitors to get a stable crystal oscillation.
Two final boards are done by now. One with crystal and one version without crystal. The version without crystal also breaks out the 2 crystal pins to the breadboard.
All components are on one side and are big enough for hand soldering with a pincer and small tip soldering iron (at least; that's how I made the boards in the picture).
Both ends accept a 6-pin USB/Serial (FTDI) programmer adapter, so you can configure the 328PB for a bootloader on UART0 or UART1, and have a serial connection on the other UART.
Or use two serial adapters at the same time and program via the ISP connector on top.
While the board is backwards compatible with the Nano-V3 footprint (except 3.3V pin) it has no built in USB.
For future readers who want this:
Attached are the Eagle boards files, that can be imported into Diptrace, Kicad, etc.
Parts list:
1 x 0805 SMD Led
3 x 0805 SMD Capacitor 0.1 uF (2x for DTR reset line, 1 for mcu decoupling)
2 x 0805 SMD Capacitor 10 uF (for AMS1117)
1 x 0805 10K resistor (for reset pullup)
1 x 0805 1K resistor (for led)
1 x AMS1117 5V regulator
50 Pinheaders
and for the crystal version:
2 x 0805 SMD Capacitor 22 pF (anything from 12-22 pF should work)
1 x 16MHz crystal
@hmeijdam Incredible! I noted your post about this on another thread recently, and just followed it up. If I make some, I'll be sure to credit you; I may start with this and go a different direction, but you and Pololu(via their A-star product) will have done the heavy lifting.
Thank you for sharing, this is what it's all about.
C
Sure. Have fun with those boards. They quickly became my go-to experimenting boards. The two UARTS are more handy than I initially anticipated and the 2 additional 16bit timers are welcome.
The board without the crystal has a downside. Ofcourse at some point I burned a bootloader to it for the crystal board, rendering it unresponsive. Then I realized the 328PB has Clock Failure Detection (CFD), which should be able to fall back to the internal resonator if the crystal fails.
No joy with that, it simply does not work, or I don't know how to use it.
I changed the boards.txt so that the CFD (extended fuse bit) is activated when burning a bootloader. I changed the CFD bit afterwards via avrdude. I opened a topic about it here
If you ever understand if/how CFD can save a board booting up without a crystal let us know! I gave up on that and promised myself to not touch the bootloader on the non-crystal boards.
One big advantage, over the bought parts, is that you can use very low IQ current regulators such that with the watchdog wake up you can get 'deep sleep' currents that average 10uA or so, so I called them ProMisers.
