Its finally here! Its been a while since I posted How To Build The 4th Doctors Sonic Screwdriver, but I've got the sound unit ready.
Step 1: Parts
Step 2: Program the Attiny
The circuit consists of an ATtiny85 connected to the speaker. I programmed mine using an Arduino Uno (more info on programming using Arduino can be found at http://highlowtech.org/?p=1695). To use the tone function you will have to use the Arduino-tiny core (which can be downloaded at https://code.google.com/p/arduino-tiny/downloads/detail?name=arduino-tiny-0150-0020.zip) To use this core copy it into the Arduino folder and rename the prospective board file to "Boards". you should have a file like this: C:\Program Files (x86)\Arduino\hardware\tiny\avr\Boards.txt.
Upload the program to the Attiny85. You can use Sonic_Screwdriver_Tom_Baker.ino for a more 4th Doctor sonic sound, or use Sonic_Screwdriver1.ino for the more modern sound.
Step 3: Putting the Pieces Together
Solder the speaker and battery plate to the Attiny, then slide that into the 3d printed case.
Solder a short wire onto the battery spring and insert it into the case across from the battery plate.
Step 4: Attaching the Switch
Solder a wire to the power pin on the Attiny. Carefully solder the switch between the battery spring wire and the attiny wire. Glue the second 3d printed piece onto the switch. (To size it correctly to the sonic, you may have to add some washers to increase the thickness)
Step 5: Finishing It Up
Remove the bottom plug from the sonic, put two AG3 batteries between the battery spring and plate, and screw the sound unit into the sonic.
If you have any questions or suggestions, I'd love to see them in the comments. If you liked this Instructable, please vote for it!