Schematic Overview
The Pyro Propeller Clock POV schematic is actually not very difficult. There are three main parts: the power supply which uses a 7805, the LED output control which uses the PIC18F252 and 74LS373 and the 'home' trigger circuit which uses an IR emitter and Phototransistor.
![](img/schematic.png)
View Full Schematic
Schematic Specifics
Power Circuit
This standard +5v power regulation circuit makes use of the LM7805 3-pin T220 device. A DC filtering capacitor is attached to its output to prevent high frequency spikes from the power supply.
LED Output Control
The PIC 18F252 uses an 8-bit data bus system with 2 control lines to tell which 74LS373 latch to output data on the bus to turn on/off LEDs. With this design, we can only send data to one 74LS373 at a time, which just means LED output updates will be nearly simultaneous instead of 100% simultaneous.
The Home Trigger Circuit
In order to know when the system should restart displaying the current image on the propeller clock, we need a known reference point called 'home'. An IR emitter diode shines bright into a phototransistor. This turns the transistor 'On' connecting the +5v collector pin to the +0v Emitter pin. The PIC 18F252 will see this 'falling edge' transition and know right away it's back at the home location, 360°.
The Pyro Propeller Clock POV schematic is actually not very difficult. There are three main parts: the power supply which uses a 7805, the LED output control which uses the PIC18F252 and 74LS373 and the 'home' trigger circuit which uses an IR emitter and Phototransistor.
![](img/schematic.png)
View Full Schematic
Schematic Specifics
Power Circuit
This standard +5v power regulation circuit makes use of the LM7805 3-pin T220 device. A DC filtering capacitor is attached to its output to prevent high frequency spikes from the power supply.
LED Output Control
The PIC 18F252 uses an 8-bit data bus system with 2 control lines to tell which 74LS373 latch to output data on the bus to turn on/off LEDs. With this design, we can only send data to one 74LS373 at a time, which just means LED output updates will be nearly simultaneous instead of 100% simultaneous.
The Home Trigger Circuit
In order to know when the system should restart displaying the current image on the propeller clock, we need a known reference point called 'home'. An IR emitter diode shines bright into a phototransistor. This turns the transistor 'On' connecting the +5v collector pin to the +0v Emitter pin. The PIC 18F252 will see this 'falling edge' transition and know right away it's back at the home location, 360°.