Electronics > Microcontrollers

A Nano of Desperation

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profdc9:
Arduino Nanos are out of stock in many places.  As a stopgap measure, I designed an alternative that uses the DIP28 ATMEGA328P-PU which has the same pinout, except it has no 3.3V supply, no ADC6 and ADC7, and is programmed using a serial USB TTL converter (FTDI or CP2102), but it has the reset circuit to control the ATMEGA328P.  You can get the gerbers at

https://github.com/profdc9/NanoDIP

I have attached an image of the PCB.  Hopefully this can be useful to someone.  As a side benefit, it makes it really easy to replace the ATMEGA328P chip because it is socketed.

fchk:
Digikey has got 1813 pieces of ATMEGA328PB-AN (TQFP32) on stock at the time of composing this text.

The layout of your PCB shows clear signs of a beginner's work. That's not a bad thing since we all started doing things at some time, but you should be aware of them:
1. The bypass caps need to be directly at the VCC-GND pin as near as possible to be effective. Even when using a DIL uC SMD caps would have been much better from an electrical point of view.
2. Same is true for the crystal. Although your design may work choosing SMD parts would have made your design more reliable since trace length could have been smaller.
3. A LM7805 is really old and has 2 volt dropout voltage. If you would use an MCP1702 your design would still work at 6V input voltage with 5V output voltage.

fchk

HwAoRrDk:

--- Quote from: fchk on October 18, 2021, 07:18:07 pm ---Digikey has got 1813 pieces of ATMEGA328PB-AN (TQFP32) on stock at the time of composing this text.

--- End quote ---

The '328PB is not directly compatible with the '328P - different peripherals, different pin-out. Not a suitable substitute when trying to make an Arduino-compatible board.

Dubbie:
What are all those funny holes all over your board? Are they huge vias?
Where are the component pads?

 ;)

westfw:

--- Quote ---The '328PB is not directly compatible with the '328P - different peripherals, different pin-out. Not a suitable substitute when trying to make an Arduino-compatible board.
--- End quote ---
The 328PB has a proper superset of peripherals, and the pinout changes consist of replacing a set of power pins with GPIO (plus the extra functions on some pins to handle the extra peripherals.)
I suspect that many Arduino-compatible 328p boards could have a PB chip dropped onto them, and no one would ever notice.  (You have to be sure not to set the GPIO pins now connected to power rails to outputs, and you might have troubles with the crystal oscillator.  But in times of shortages, it would be worth a try, IMO.
(There are also a couple of designs out there where the Nano has been modified to match the PB pinout changes.  It is an open source design, so that's pretty easy.  (disconnect a couple pins from the power rail, essentially.)  Although actually assembling an SMT NANO isn't so easy, for many of us.)

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