Low-tech and High-tech POV (Persistence of Vision)
Introduction: Low-tech and High-tech POV (Persistence of Vision)
Persistence of vision is an optical illusion. When we look at an object, our eyes keep seeing an image of it for a fraction of a second after the object is removed. If several images appear quickly after each other, they seem to merge.
My low-tech example is a piece of cardboard with vertical lines on one side and horizontal lines on the other. When it spins, a word becomes visible.
The high-tech example has a small computer and a single row of LEDs that flicker in a specific order. When the LEDs are moved sideways quickly, letters appear and form a word. The result is best seen in the dark.
A very good video of other low-tech examples may be found onYouTube in “What is Persistence of Vision? (Mr. Wizard)” https://www.youtube.com/watch?v=YismwdgMIRc
Parts for the Low-tech Example
1. Long shish-kabob stick or knitting needle or similar stick
2. Corrugated cardboard
3. Paper for printing
4. Labels
5. Clear tape
Parts for the High-tech Example
1. A computer (I used an Apple iMac)
2. Arduino Uno or another model and its USB cable
3. Breadboard, preferably attached to the Arduino
4. 5 LEDs of the same color
5. 5 resistors 220 ohms
6. 10k resistor
7. Push-button switch
8. Small piece of thin cardboard
9. 51
Paper clip
10. Small piece of electrical tape or duct tape
Step 1: Make the Low-tech Example
Choose a word and print two copies. The font for my HELLO sign is 144-point Bank Gothic.
Cut some labels and stick them on the copies of the word, such that one copy has only vertical lines and the other has only horizontal lines.
Decide on the size of the sign. The long dimension has to be shorter than the length of the shish-kabob stick. Cut the corrugated cardboard, with the corrugation holes running lengthwise, and making sure that one of the corrugation holes is in the exact middle. Cut the two paper copies to the same size, being careful that one copy will align on one side of the cardboard exactly with the other copy on the other side.
Attach the copies to the cardboard. I used labels and covered the long edges of the cardboard, so that the brown edges don’t show when the cardboard spins.
Push the shish-kabob stick down the exact middle hole of the cardboard, with both ends sticking out.
Spin the finished sign with your fingers, holding both ends of the shish-kabob stick.
You could also put one end of the stick in a power drill and spin it. This gives a very good result.
Step 2: Wire the Arduino
If you’re not familiar with the Arduino, the following links may be useful:
Getting started with Arduino: https://www.arduino.cc/en/Guide
https://www.instructables.com/A-Beginners-Guide-to-Arduino/
Online Arduino class: https://www.instructables.com/Arduino-Class/
The circuit is shown in the photo and described below. I used several wires to make the connections.
1. Arduino’s +5V goes to + on the breadboard
2. Arduino’s GND goes to - on the breadboard
3. The five 220 ohm resistors go from pins 2 thru 6 of the Arduino to separate pins on the breadboard
4. The long wires of the five LEDs go to those pins on the breadboard, and the short wires go to - on the breadboard
5. The 10K resistor goes from the Arduino’s pin 7 to - on the breadboard
6. The push-button switch should be placed in an outside corner of the breadboard, so that it can be pressed easily. One side goes to the 10K resistor that goes to pin 7
7. The other side of the switch goes to + on the breadboard
8. Cut a small piece of cardboard (bent in the middle) to fit onto both sides of the LED wires, and attach with a paper clip. This will keep the LEDs from flopping around when moved back and forth quickly.
9. Stick 2 pieces of electrical tape or duct tape, one on top of the other, over the green light of the Arduino.
Step 3: The Arduino Sketch (The Code)
The code was downloaded from a Hackster project titled “Arduino Horizontal POV Display” https://www.hackster. 635