MiniMegaZero24 (megaAVR-0)

 ### Features * Breadboard friendly * A little more minimal circuit than other currently available devboards/designs * Designed for battery operation running at 8MHz at 3.3V * MCP1700 or MCP1702 voltage regulators with very low quiescent current * Draws about 5uA current when ATmega and NRF24L01+ are sleeping and GPIO pins 2 to 25 set to INPUT_PULLUP (1608 draws slightly less than 4808) * Mostly 0805 footprints for easy soldering * Should be compatible with megaAVR-0 ATmega808, 1608, 3208 and 4808 (tested with 1608 and 4808) * The MCU used in this design is the same as on the AVR-IOT WG and similar to the one on the Arduino Nano Every (basically it only has less pins than the 4809) * NRF24L01+ SMD module (optional) * Use FTDI programmer (e.g. a cheap FTDI Basic 3.3V from Sparkfun) for flashing sketches and serial monitor in Arduino IDE, like on Arduino Pro Mini **WARNING**: Do not connect a **5V** FTDI board to the circuit when a NRF24L01+ is present in the circuit. Otherwise you may fry your NRF24L01+. Only use **3.3V** boards A cheap P-Channel MOSFET with low RDS(on) is used for reverse polarity protection, because unlike diodes it does not have voltage drop. MOSFET: AO3401A by Alpha & Omega Semiconductor Inc. See this video about how this reverse polarity protection works: [https://www.youtube.com/watch?v=IrB-FPcv1Dc](https://www.youtube.com/watch?v=IrB-FPcv1Dc) Another OSHW board with the same MCU (but without FTDI connector) can be found here: [https://oshwlab.com/wagiminator/atmega4808-development-board_copy](https://oshwlab.com/wagiminator/atmega4808-development-board_copy) - - - ### **Flashing the MegaCoreX bootloader through UPDI** Download the bootloader hex file from here: [https://github\.com/MCUdude/MegaCoreX/blob/master/megaavr/bootloaders/optiboot/bootloaders/mega0/115200/Optiboot\_mega0\_UART0\_DEF\_115200\_A7\.hex](https://github.com/MCUdude/MegaCoreX/blob/master/megaavr/bootloaders/optiboot/bootloaders/mega0/115200/Optiboot_mega0_UART0_DEF_115200_A7.hex) Download pyupdi from here: [https://github.com/mraardvark/pyupdi](https://github.com/mraardvark/pyupdi) Flash the bootloader using your **FTDI board** **connected to the UPDI pin** like this (see schematic below): ``` python.exe pyupdi.py -d mega4808 -c COM3 -f Optiboot_mega0_UART0_DEF_115200_A7.hex  -v -b 115200 ``` Set BOOTEND fuse like this: ``` python.exe pyupdi.py -fs 8:0x02 -c COM3 -d mega4808 ``` Set SYSCFG fuse like this: ``` python.exe pyupdi.py -fs 5:0xc9 -c COM3 -d mega4808 ``` Set OSCFG fuse like this (I'm not sure if this was necessary) ``` python.exe pyupdi.py -fs 2:0x01 -c COM3 -d mega4808 ``` In the above 4 lines, replace -d mega4808 with -d mega1608 if you're flashing an ATmega1608 with the bootloader. Add this URL to your **Additional board manager URLs** in Arduino IDE and install the MegaCoreX boards in the **Boards manager**: ``` https://mcudude.github.io/MegaCoreX/package_MCUdude_MegaCoreX_index.json ``` Set the following board options in Arduino IDE: * Board: ATmega4808 * Clock: Internal 8MHz * BOD: BOD 2.6V * Pinout: 32 pin standard * Reset pin: Reset * Bootloader: Optiboot (UART0 default pins)

- - - ### Uploading Sketches and using NRF24L01+ Use the FTDI connector to upload sketches and use the serial monitor, like you would use it on a Arduino Pro Mini. After flashing the bootloader the UPDI pin isn't necessary anymore. For the NRF24L01+ use the RF24 library by TMRh20: [https://github.com/nRF24/RF24](https://github.com/nRF24/RF24) Initialize it like this: ``` RF24 radio(9, 7); ``` The IRQ pin of the NRF24L01+ is connected to GPIO pin 10 on the ATmega. - - - ### Sources/more information * [https://www.microchip.com/wwwproducts/en/ATmega4808](https://www.microchip.com/wwwproducts/en/ATmega4808) * [http://ww1.microchip.com/downloads/en/DeviceDoc/ATmega4808-4809-Data-Sheet-DS40002173A.pdf](http://ww1.microchip.com/downloads/en/DeviceDoc/ATmega4808-4809-Data-Sheet-DS40002173A.pdf) * [http://ww1\.microchip\.com/downloads/en/DeviceDoc/ATmega4809\_Curiosity\_Nano\_Schematics\.pdf](http://ww1.microchip.com/downloads/en/DeviceDoc/ATmega4809_Curiosity_Nano_Schematics.pdf) * [http://ww1\.microchip\.com/downloads/en/appnotes/atmel\-2521\-avr\-hardware\-design\-considerations\_applicationnote\_avr042\.pdf](http://ww1.microchip.com/downloads/en/appnotes/atmel-2521-avr-hardware-design-considerations_applicationnote_avr042.pdf) * [https://github.com/MCUdude/MegaCoreX](https://github.com/MCUdude/MegaCoreX) * [https://github.com/mraardvark/pyupdi](https://github.com/mraardvark/pyupdi) * [https://oshwlab.com/wagiminator/atmega4808-development-board_copy](https://oshwlab.com/wagiminator/atmega4808-development-board_copy)