Optical Noise Rejection Circuit
Original Publication Date: 1985-Nov-01
Included in the Prior Art Database: 2005-Feb-19
In a system where the processor is coupled to a keyboard through an infrared (IR) serial data link, optical noise transmitted by fluorescent lights may trigger the IR receiver, thereby causing false interrupts or timing errors. The fluorescent noise, which is periodic, consists of impulses separated by 300 microseconds (msec) which are rejected through the use of the dual monostable multivibrator circuit shown in Fig. 2. As shown in Fig. 1, a 10-bit serial word is generated for each make or break action of a key of a keyboard. This word is then Manchester encoded and transmitted in the form of three pulses at the beginning of each encoded "0" half bit. The dual monostable circuit (Fig. 2) is used to recover the encoded waveform from the received pulses and to reject the periodic fluorescent noise signals.