Propeller Clock

Topics: Light-emitting diode, Diode, LEd Pages: 4 (758 words) Published: August 24, 2013



Persistence of Vision

Propeller Clock

• Introduction • Parts • Circuit • Making • Contacts

The propeller clock is a linear array of light emitting diodes, rotating at a high angular velocity to generate a circular screen.

“What we see is a blend of what we are viewing and what we viewed a fraction of a second before” Persistence of vision: For example, if ‘1’ has to be displayed, then the series of lighting up of diodes would be like following:

Now by synchronising these light emitting diodes, and keeping in mind the concepts of persistence of vision and limit of resolution, we can display a clock.

Related videos on ‘Persistence of vision’:

Limit of Resolution

Basically, it has 2 units:


Rotating board and DC motor with power supply unit:

1. Rotating circuit board 2. DC motor with power supply unit

The rotating board has several primary parts. It includes 1 microcontroller ‘ATMEGA16’, 19 LEDs, 2 capacitors of 2200 μF each, 1 infrared LED, 1 TSOP1738 sensor, 1 rheostat of 10kΩ, resistances of 220Ω and 5kΩ, insulated copper wires and connecting wires.

The power supply unit is actually a slip ring as 1 electrode and a contact wire attached to motor shaft as the other electrode. It has 7805 IC for 12V and 5V regulation to motor and board respectively. There is a small piece of mirror to act as a trigger point of remote sensing.

The following is a schematic diagram of the circuit of the propeller clock:


The motor rotates at a quasi-constant angular velocity (about 1000 rpm). The MCU generates a 38kHz pulse for the IRLED which the mirror reflects once every rotation and is sensed by TSOP sensor to trigger an external interrupt which counts the number of microseconds elapsed between 2 successive...
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