on this page i want to describe how I built my circuit board business card.
Since there are several business cards made of circuit board on the Internet already, I thought of making my own. There are some with built-in USB stick or sometimes only as a simple layout.
Looking for a suitable electronic touch, I remembered the game "Simon Says", also known by other names.
After a short browse through the net, finding various simple implementations on a all kinds of microcontrollers I started creating my own.
- PCB material from Bungard, 35μm copper layer, black dyed FR4 (epoxy + fiberglass); usually the base material is brown, but I thought that black material later gives a nice contrast.
- Atmel microcontroller Attiny 45: One of the smaller µC, but with full ISP, which later simplifies the programming
- SMD LEDs and resistors in 0805 format
- SMD switches, slide switch, and battery holder for a CR2032 lithium battery (3V)
First I designed the circuit and layout with Eagle. The actual circuit is very simple, 4 LEDs with resistors of 330 ohm at 4 I/O pins.
Since only one input and the reset pin on the Attiny is left , I decided to attach the 4 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 programm.
Schematic and Layout in Eagle Layout Editor
The "photo" and contact details were created with Photoshop. To save etching the picture is framed by some sort of honeycomb pattern. Once the finished layout in Eagle had been exported to a PS file, the picture and the layout were merged in Photoshop.
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.
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 smeares.
The ideal transfer medium to me is the back of wrapping paper used for presents. It has a slightly waxy surface and can be removed completely from the copper board after lamination. I just glue a piece of wrapping paper on a page of A4 standard paper, so there are no paper jams.
Layout printed on paper
Before the layout is laminated onto the board, it is important to clean the board and degrease it. In my case I use acetone.
After that, the transfer follows. On the Internet, many people use a converted paper laminator. However, I use the fuser from an old laser printer. Inside it is heated by a halogen lamp. The feed consists of a gear and an old furniture knob.
Fuser from old laser printer
After the board went through the laminator a couple of times and the toner has been deposited on the copper, it's time to remove the wrapping paper. This is done under running water. The paper can easily be removed without residue.
Remove paper under running water Layout is now applied to copper
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.
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 completly.
There was a lot of copper left in the area of the image, so the right part of the card was covered with some tape and put back into the etching bath until all free copper surfaces were dissolved.
Then the card is removed from the etching solution, and rinsed with water.
Card in etching solution(photo by prototype)
Cleaning and tinning
Now, the toner has to be removed from the board. For this purpose, I used acetone again.
Toner and residues of adhesive tape must be removed completely
In order to obtain a nice contrast the card was then completely tinned. For this purpose I use solder paste from the hardware store,
which is meant to solder copper pipes.
The paste is applied evenly to the copper and heated with a heat gun for about 1 minute, until a thin layer of tin has been deposited.
Then the board can be cut and cleaned again.
Assembly and Programming
After tinning the card, a quick check for broken traces or shorts to the ground plane follows. The easiest way to do this is with a multimeter and continuity tester or resistance measurement.
The assembly follows. Even with a fine tip soldering iron at hand it is not quite easy to deal with components in 0805 (2 mm x 1.25 mm) format , a good eye and steady hand is quite necessary.
Finally the card has to be programmed. The Attiny is connected to an ISP (in my case an Arduino Duemillanov with matching ISP sketch).
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. Instructions to do this can be found on the internet.
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, eg by decreasing battery voltage, an upper and lower limit for the respective key has to