Rotating LED Display - Alan Parekh’s Electronic Projects


Rotating LED Display

The left image is with the lights off the column of LEDs are rotating in a circle displaying the word “LEDS”. On the right this image is with the lights on, the board can be seen rotating very quickly and a word appearing in mid air!

VIDEOS

Watch a video (1 MB) of the rotating display operating in the light!

It is hard to see the display in the light since the LEDs being used are not super brights, they are just standard LEDs. The camera also seems to have a strange effect on the video, in the video you can see partial pieces of the unit as it rotates. This is not the case when you watch it with the naked eye.

Another video (4.4MB) this time it is in the dark.

The video camera has a bad effect on the display, the display is actually solid, there is no odd sweep of black around the display. Must be the same effect that you get when you video tape a monitor (the rolling black bar).

Another video (4.5MB) moving around the display while it is running.

There are many words that are displayed that are not entirely visible when seen from a single angle, this video shows that some words wrap around the display.

BACKGROUND

Is this an original idea? No. The propeller clock by Bob Blick was the inspiration for this display, the concept is the same but instead of just number I am displaying letters. Take a look at the links for more examples of similar devices.

OPERATION

This unit has a single column of LEDs that are spinning in a left to right motion, as it spins a microcontroller keeps track of the exact position of the board. Words are written in the air by flashing the correct bit pattern in the correct location. The same word is repeated over many revolutions of the device, each time the LEDs turn on in exactly the same locations. This works because of something called persistence of vision, the eye retains the image for a split second. This is also the same principle that makes the hard drive clock work. When looking up information about the persistence of vision phenomenon I stumbled across another phenomenon called after images, you must try it.

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ROTATING DISPLAY PICTURES

This is a long exposure shot with a regular digital camera.

The LEDs are too directional, that is why the center appears brighter in this picture.

This is the start up sequence, it is blurred because of the long exposure. It should look like 2 circles with spinning lines inside.

You are able to see the letters as well as the board spinning very fast.

Close shot of the display in low light.

Look closely at this picture or you will miss it, this was taken with the camera in flash mode while the sign was operating, look to the right of the column of LEDs you can see a faint portion of the display!

Low light picture.

Taken from above, notice the circular blur of the sign spinning.

Another low light picture.

 

Picture of the device from the front.

Top picture, the microcontroller and oscillator are on the left of the board close to the LEDs.

The back end had to be weighted down to allow it to run smoothly

 


Left side.

Front.

The motor is a 6V DC motor.

To the right of the motor in this picture is a metal post that breaks an infrared beam sensor. This is how the unit knows where it is in a revolution.

The board gets it’s negative from the motor. the shaft to case has a low enough resistance to work fine. The positive is provided by a copper ring and a sweep arm.

The sweep arm is visible. it is to the right of the motor.

18V DC is brought in to the terminal block.

A variable voltage regulator is used to adjust the speed of the motor. The 6V motor is being powered at about 3V. You might notice that the board holding the column of LEDs is broken and stiffened. This is because the crystal flew off on one of the first full voltage unbalanced tests and broke the column of LEDs.

Power is connected to the motor from underneath.

 

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