For many of my previous projects I used AVR Microcontrollers extensively. I started with the Atmega8 and moved to superior AVR variants depending on the application complexity and requirements. Before designing any particular application, I usually do my research on a development board. It is a PCB featuring the target microcontroller and minimal support logic that usually covers a regulated power supply, pin headers to connect peripherals and/or a few LEDs used for basic debugging.
Such boards are available in many shapes and colors, from simple to complex and most of the times they are affordable (after all we’re talking about a minimal PCB with a microcontroller and a few, mostly passive, components).
For some various reasons I had to design my own core development board featuring an Atmega128A-AU microcontroller from Atmel. This is an excellent piece of silicon, featuring 128KB of flash memory, a max operating frequency of 16Mhz and a generous total count of 64 pins offering plenty of I/O options.
When doing prototype PCBs I usually go for a toner transfer manufacturing process, that might have its issues but can prove reliable once you get it right.
Development board schematics and PCB
This was rather simple to do: designing a board that connects most of microcontroller’s I/O ports to pin headers, and for the rest traces to a main 8Mhz quartz crystal, a voltage regulator (AMS1117), a DC Jack, a reset button and a LED to show when power is connected. There is a second 32.768KHz crystal that I plan to use with the Atmega128’s internal real time clock circuit.
Toner transfer tips
There are many tutorials on how to create PCBs using toner transfer, so I will not waste time with redundant information. Instead here are some tips that for me at least, made the process easier.
-1-Clean the copper!
Before transferring the toner, do a zealous job at cleaning the copper surface. Use abrasive paper, abrasive brush or any other mechanical means of cleaning the surface, but try not to scratch it. So if using emery paper, make sure the granularity is soft. Deep scratches can prevent toner form reaching the copper surface and forming a good bond, resulting in interruptions in your traces. Avoid that at all cost.
Once you get a nice shiny surface, clean it with acetone. I used to skip this step, and later I realized that grease will prevent toner from sticking to the copper. So acetone is a must.
Read More: DIY AVR Development Board with Atmega128