DIY Arduino mega

So, there is plenty of documents and tutorials for making a diy UNO. But does anyone know how to go about making a diy mega?

I did find this chip

But how would we go about setting it up to use as a microcontroller and how would we program it? I like the DIT uno because i can just take the chip straight out of my uno, and put it back it to program.

Everything is online.
What do mean with "mega" ? The Arduino Mega 2560 board or a common ATmega chip ?

When you make a Arduino compatible design, select one of the microcontrollers that is supported by Arduino. For example the ATmega32U4 is used in the Leonardo.

The schematic is on that page, and you can copy that if you want to.

Somewhere in the Arduino folder is a file "boards.txt", that contains the supported boards and microcontrollers.

If you want something small, why not use a smd version of the ATmega328P ?

To program it, you can write a bootloader into it. The bootloaders for the Arduino boards are also somewhere in the Arduino folder. If you want to use a chip that is not supported by Arduino, you can make your own bootloader with Optiboot.
A programmer (Arduino Uno as Arduino ISP or USBasp V2, or other programmer) is needed to burn the bootloader or to write the sketch without bootloader. When the chip has a bootloader, the RX, TX, DTR signals can be used to upload a sketch without programmer.

I think what he’s asking about is why there are tons of instructions on how to build an Uno compatible board at home, but not for how to build a Mega (as in Arduino Mega, the board with the atmega2560) compatible board at home.

The reason is that the 2560 is only available in surface mount packages that can’t be used at home without fabricating an appropriate printed circuit board to solder them down onto - and the soldering is a little intimidating to boot.

The largest atmega chip that comes in a DIP package is the 1284p (DIP-40; I think it gives you 32 GPIO pins?). Making a DIY 1284p at home is same as making a DIY uno - there’s a core for the 1284p available (a few people on here love them, they’ve also got the most sram of any atmega part)

In that case, go here : Cross Roads Electronics

Proto Advantage sells a 64-pin DIP adapter board for the most friendly size of the Mega2560 (0.8mm pitch 64-pin QFP) for hand soldering.

edit: I guess you don’t get all the functions with the 64-pin package? Proto Advantage sells a 100-pin adapter as well which fits one of the Mega packages. The pitch is 0.5mm pitch.

I’ve made up some PCBs for a minimal 2560 board, all IO broken out, FTDI interface, ICSP interface, crystal, caps, reset pullup, decoupling caps.
I have 2 2560s at home, will get around to assembling them one of these weekends.
I think I’ve posted pics of the board before, but here’s the board layout. I added 2 more jumpers so that DTR could be disconnected, and 5V accessible also.