Summary and Materials
My, I am very happy to say, successful plan was to produce a 3D
Zoetrope using skills
learned in the Fab Academy; computer aided-design, computer controlled cutting, electronic design,
3d molding & casting, 3D printing, embedded programming, input and output devices, mechanical and machine design.
- Main PCB is the output devices speaker board.
- Two LED boards with eight bright LEDs for strobing
- Hall effect switch board mounted under the board with magnets
- Spindle Speed Control voltage divider board to control spindle speed.
- Spindle on motor salvaged from a
- Platter with eighteen magnets placed equally round perimeter.
- Mounting platform for mounting spindle and motor, platter, and all the
- Eighteen 3D printed and / or cast characters.
Using the speaker circuit board from the output devices assignments
which has a Mosfet and Attiny45. Changed the
on this Attiny45 was from 8 mHz to 16 mHz to get a higher clock rate.
Milling platform and printing necessary parts
Milling a two-sided board
- Side one: For aligning characters, routed lines in board in proportional divisions.
- Side one: Drilled thru (alignment) holes in four corners of the board
to align the board when flipping board.
- Side one: Milled out square and remove from ShopBot leaving the left over material attached to
sacrificial layer of ShopBot.
- Side two: Flip square over aligning holes and screw to sacrificial layer of ShotBot.
- Side two: Do not change the x or y zero settings.
- Side two: Mill magnet pockets with smaller offset pockets to make it easier to remove the magnets.
- Side two: Mill final circle shape.
- With careful planning the "side two" magnet pockets were centered over lines on "side one".
Click an image to enlarge
The bright white LEDs each need 20 mA constant current, and a
forward drop voltage of 2.8V (found in the LED datasheet).
At 9V DC we would need a resistor of: E = iR E = 9V and i = 20 mA
Solving for R:
|R = E/i or (9V - 2.8V)/20mA
|6.2V/(20A x 1/1000)
|(6.2V x 1000)/20A
|6.2 x 50 Ohms
two LED board for strobing
Check calculations with online
Formula to use resistors in the Fab Lab inventory:
|Rp = 1/(1/R1 + 1/R2 + 1/R3 + … + Rn)
|499 Ohm and an unknown resister in parallel: 310 =
1/(1/499 + 1/Ru)
|1/310 = 1/499 + 1/Ru
|1/Ru = 1/310 - 1/499
|Ru = 1/(1/310 - 1/499)
|Ru = 818 Ohm, closest greater value on hand is 1
kOhm giving a total resistance of:
|Rp = (1/499 + 1/1000)
|Rp = 333 Ohms
Spindle Speed Control
The spindle is from an old Sony turntable. These old turntables
have a magnetic strip painted around the rim under the platter,
which is read by a tape head, this is how the turntable achieve speed
control. This was no help to me, the Zoetrope speed is controlled using a Voltage
Interrupts and timing
Using one interrupt which happens every twenty-five micro seconds to check the state of the system (Zoetrope's strobing LEDs). The system has five states; START, WAIT, LOW, HIGH, DWELL.
Reference on interrupts
Comparing Hall Effect Sensor and Hall Effect Switch
Hall effect sensors detect whether a magnet is near. Holding a
magnet near the sensor will cause the output pin to toggle. However
Hall Effect Sensor from the Fab Lab inventory did not have the
sensitive the Zoetrope needed. After reading the data-sheets and comparing a hall effect sensor and
hall effect switch the Zoetrope uses the ultrasensitive
The board with the Hall effect switch is mounted under
the platter of magnets to switch on/off the LEDs
- When making multiple items always test with one.
I made all the molds for the character all at once. Meaning that I forgot spray all the molds
with mold release.
- Re-using the speaker circuit board saved time but designing
the board to use an Attiny44 would have give more
- After months of second guessing my measurements I finally got a handle on the metric system.