• Modulated Light DX Receiver Circuitry
• OPTICAL COMMUNICATION FOR THE AMATEUR  by Chris Long, originally published in Amateur Radio magazine by the Wireless Institute of Australia, Melbourne, January 1979.
• A Low-Noise PIN Diode Laser Receiver!  by K3PGP
• A Comb Filter to Remove AC Hum from Mains-Powered Lighting in an Optical Receiver
• AVR Digital Comb Filter (humnuller)  by Dan Stahlke
• ATmega168 Information
• Schematic
• HUMNULLER.BIN  60 Hz
• PIC Humnuller  by Karen Orton
• PIC16F876-04  Ran at 20 MHz
• PIC Files