”First I designed the circuit and layout with Eagle. The actual circuit is very simple: four LEDs with resistors of 330 ohm at 4 I/O pins,” Bach wrote in a recent blog post.
“Since only one input and the reset pin on the Attiny is left, I decided to attach the four buttons for input through multiple resistors to an A/D input. Depending on which push-button/resistor combination is pressed, a different value between 0 and 1023 can be read on the A/D input. This value is mapped to a button in the program.”
According to Bach, the photo and contact details were created using Photoshop, with the image framed by a honeycomb pattern. Once the finished layout in Eagle was exported to a PS file, the picture and layout were merged.
“To put layouts on copper board, I use the toner transfer method. The layout is printed by a laser printer and melted with a laminator onto the board,” he explained.
“In order to obtain useful results, the choice of paper on which the layout is printed is crucial. The toner should not be absorbed too much by the paper, but adhere enough to the paper so that nothing smears.”
Before the layout was laminated, Bach cleaned the board and degreased it with acetone. He then proceeded with the transfer, using a fuser salvaged from an old laser printer.
“The board is etched in a sodium persulfate solution, which is heated to about 40 degrees Celsius. The process takes about 20 minutes, swirling the solution supports the etching process,” he continued. “In order to avoid etching away the fine copper traces, I took the card out of the etching bath after the actual circuit was etched completely.”
“This little game was also created with the Arduino IDE. Appropriate board settings for ATtiny µC have to be loaded into Arduino IDE before they work with the IDE,” he concluded. ”The required A/D values for the keys were recorded via an analog input of the Arduino and entered into the final program. Since the A / D values vary slightly by decreasing battery voltage, an upper and lower limit for the respective key has to be specified.”