Introduction: Arduino Controlled Pocket Etch a Sketch Random Walk Simulation

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This project is the result of Wal-Mart check-out lane impulse purchase of Pocket size Etch A Sketch for $3.99.

Two stepper motors drive Etch A Sketch knob shafts, and a servo motor flips Etch A Sketch to erase the screen.  Using the Arduino IDE’s Serial Monitor the user can automatically generate “random walk” simulations. Material cost  about $60, simple construction requires only a couple hours effort.

Not a true random walk simulation since it separately moves random amounts in horizontal and vertical directions; and maximum travel is restricted to remain within Etch A Sketch screen.

Time lapse video took about 30 real time minutes.
http://youtu.be/i865f9H5Bug

Etch A Sketch Flipping Video:
http://youtu.be/SXlB8tjRym8

Step 1: Procure Hardware:

See pdf file for detailed listing of stuff you’ll need.

For the Arduino board, I actually used a Freeduino board, although I initially developed the project using an Arduino Uno board.  Both these Ardunio boards can be powered directly from USB.

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Step 2: Mechanical Assembly

Step 1: Drill 9/64 hole in one side of the 1” nut (this will be the Counterweight).  Drill a 9/64 hole in the sidewall of 3/8 ID Nylon bushing, see photo.

Step 2: Cut a 130 mm by 132 mm piece of 1/8 plywood and drill five 9/64 holes per figure 1. Mark a servo pivot axis line 50 mm from top on board back side. Cut 3 pieces of ¾ inch square stock wood  ¾” long.  In one piece drill a 9/64 hole per figure 2. Cut a 1” long piece from 1” square stock wood and drill two 3/8 holes per figure 3. Cut a 150 mm by 200 mm piece of ½ plywood and drill two 3/8 holes per figure 4.

Step 3: Install 1 ½ long 6-32 screw into hole of ¾ ”  wood piece, secure with lock washer and nut. Using wood glue, attach  to 1/8 plywood piece, use servo pivot axis line as a guide.  The screw should be 10 mm above the plywood – same as the servo motor drive shaft.  Also using wood glue, attach  the other two 3/4 inch  blocks to opposite side of the plywood, positioning them as mounts for servo motor,  assure alignment with servo pivot axis line .  Allow wood glue to dry overnight.  After glue dries, attach servo motor using hardware included with servo motor, see photo.

Step 4: With #2 screws and epoxy, attach over the 3/8 hole, the servo horn (wheel) to 1” square wood piece, see photo.  The 3/8 “side hole” will allow you to later install the horn to servo shaft mounting screw.

Step 5: Cut 2 pieces of vinyl tubing 0.25 OD X 0.17" ID x 20 mm long.  Pry off Etch A Sketch knobs and using super glue attach each tube to knob shafts. Attach stepper motor shaft to other tube ends, secure with wire wrap.  Using 2 ½ long 6-32 screws, nuts, flat and lock washers, and double stick foam tape (between Etch A Sketch and plywood) attach stepper motors and Etch A Sketch to 1/8 plywood, see photos. Gradually tighten screws to assure good stepper motor to Etch A Sketch knob shaft alignment.







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Step 3: Mechanical Assembly Continued

Step 6: Put 2 carriage bolts thru 3/8 holes in ½ plywood base plate and fasten with nuts and flat washers. Add 4 rubber feet to corners of base to prevent rocking on carriage bolt heads, see photo.

Step 7: With servo motor shaft rotated fully clockwise (as viewed from the front of the shaft) attach the 1” block to servo motor using horn mounting screw so that the block’s vertical hole is nearly straight up, see photo. You’ll probably need a bit of trial and error to  get this properly positioned. Slide the bushing in place over 6-32 screw, see photo.  Slide both bushing and servo block over 3/8 carriage bolt uprights and secure with nuts and washers so that the Etch A Sketch is level, pivots freely, and the lower edge of 1/8 plywood is 30 mm above the base.

Step 8: Mount 1 inch nut as a counter weight to top of 1/8 plywood using 4 inch long 6-32 screw, nuts,  lock , flat and fender washers, see photos.

Step 4: Wiring, Programming and Operation

Step 9: Assembly the wiring harness per figure 5.  For Arduino to Stepper Control board signal cable, use 4 conductor ribbon cable with 4 pin male header on one end and 4 pin female header on opposite end.  I used solid core hook up wire for the other connections.  Once the wiring is complete, secure with hot glue the Arduino, Stepper Control boards and power jack to the base, see photo.  Check that wiring is routed to avoid binding as the Etch A Sketch pivots backwards.

Step 10: Copy program (Stepper_Motor_Example_Keyboard.pdf) into Arduino IDE and upload to Ardunio board.  Attach 5VDC 1 Amp or greater power supply to power jack.  After program uploads, open Arduino IDE Serial Monitor (can be found under Arduino IDE Tools menu).  The Etch A Sketch can now be controlled by typing commands at the top line of the serial monitor. The commands, all lower case single characters  are:

l  jogs the Etch A Sketch “pen”  about 2 mm to the left
r  jogs the Etch A Sketch “pen”  about 2 mm to the right
u  jogs the Etch A Sketch “pen”  about 2 mm to the up
d  jogs the Etch A Sketch “pen”  about 2 mm to the down
c clears Etch A Sketch by flipping it backward with servo motor
x  begins Etch A Sketch random walk simulation WARNING – don’t use this command unless the pen is centered on the screen. I typically use “ l , r , u , d ” commands to initially center pen on screen, then “c “ command to erase, and finally start random walk with “ x” command.
h  returns Etch A Sketch “pen”  to original position following a random walk.

Hit  return key to send commands to the Ardunio, otherwise nothing will happen. Also, you can stack commands, that is “xhc” will run random walk simulation, then return pen to original position and finally flip the Etch A Sketch to erase it.

Enjoy !!

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