Step 5: Assemble electronics
I included picture of the PC board version (with sensor/buzzer not connected) as well as a prototyping version built on a breadboard for reference. The breadboard version also shows how to connect the Arduino board as a USB programmer for the microcontroller chip. Since I used a DIP socket for the chip, I can also remove the chip and put it in an Arduino board to program it, but it can be tricky to pull the chip out without bending all the pins -- thats why i included the female header pins for the tx/rx. Even though the board is very cramped, you can see that all of the pins of the controller have a solder pad available to connect to. Since they aren't necessary for this project I did not solder female headers to the unused pins but if they were, you would have the full capabilities of an Arduino Diecimilia except on-board USB in a very small package. The width of the board is approximately one half of the Diecimilia board and about the same length. (here is a similar setup.) It is optional to use a transistor to power the buzzer, the Arduino can provide enough current from the pin itself. However, using the transistor allows you to use other sound making devices other than a buzzer if you have one.