The Scream

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Introduction: The Scream

About: I work as software engineer in one of Bay Area (California) companies. Whenever I have a time I like to program micro controllers, build mechanical toys, and make some home improvement projects.

It is Halloween decoration: the ghost image with dynamic control over its light intensity. In the video above you can see in on the right. It is installed in our window together with my other projects: "moon with a bat silhouette" and "pumpkin".

Supplies

  • Two LED Flexible Silicone Neon-Like 1 Meter Ice Blue LED Strips (adafruit.com).
  • Four white LED backlight large modules (adafruit.com).
  • Attiny85 microcontroller (any electronic supplier).
  • LM2596 DC-DC Buck Converter Step Down Module Power Supply Output 1.23V-30V (amazon).
  • NTE196 NPN transistor (Fry's).
  • Four resistors 110 Ohm 0.25 W.
  • One resistor 270 Ohm 0.25 W.
  • Breadboard, some wire, headers, heat shrink tubes, black foam Elmer's sheet, some cardboard.
  • Power supply: 110 VC AC - 12 V DC (>= 2 A output).

Step 1: Circuit

Project is powered by 12 V DC power supply (2A output is more than enough). 12 V required to power up LED strips. Chip and backlight modules are powered by 5 V which is produced out of 12 V by step down power module based on LM2596. Attiny85 controls backlight LED modules directly. Power output of chip is not enough to control strips so I added NPN transistor (NTE196 is too powerful here but it is only what I could find at the local Fry's store. I think any NPN transistor with output current > 1.6 A will fit).

Step 2: Circuit Mount

To save some time on soldering I mounted circuit on the breadboard. Pay attention to custom made adapter (around row 25 on the photo). It allows to attach AVRISP II 6 pin header to the breadboard.

3/22/2021/ Update.

Moved components from experimental breadboard to Adafruit Perma-Proto 1/4 sized breadboard permanently soldering them.

Step 3: Making the Body

Flexible LED strips arranged on the Elmer's board to form the ghost body. Then with awl I made holes in the board and moved some wire loops through holes attaching strips to the board.

Step 4: Making Face Elements

I made face elements mount with the help of cardboard in the manner of three layered sandwich. On the photo you can see middle element. It contains opening to match backlight modules. Another layer is a plain piece of cardboard behind: both attached together with wire. Front layer is actually foam Elmer's board with ghost body already attached. I cut there opening for eyes and mouth and attached face module to the board with wire loops. LEDs wires as well as strips wire I inserted into corresponding holes of the circuit breadboard.

Step 5: Programming

Program is written in C language and compiled with the help of AVR Studio 7. Studio allowed me to connect to the Attiny85 chip through the AVRISPII interface device, clear value of CKDIV8 fuse to raise controller frequency to 8 MHz, and load program into chip memory. Source code as well as supplemental materials available: https://github.com/jumbleview/casper.

Step 6: Naming the Project

Now the project is finished. I made it after friendly ghost Casper, but when I as soon as I done with it there came a feedback that it looks less like Casper but more like person from Edvard Munch "The Scream" painting. So be it. Let us name this project "The Scream".

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