Chapter 8. Advanced Experiments
8.10. Experiment with Infra-red Remote Controller
Remote controller is widely used in daily life. Most of the consumer electronic product equipped with infra-red remote controlling facility. The remote controller basically is a simple transmitter of coded key signal, inside which transmitter IC is generally used for encoding. In this experiment, transmitter IC µPD6121 is used.
The µPD6121 is infrared remote control transmission ICs using the NEC transmission format that are ideally suited for TVs, VCRs, audio equipment, air conditioners, etc. By combining external diodes and resistors, a maximum of 65,536 custom codes can be specified. The IC comes in small packages, thus facilitating the design of light and compact remote control transmitters.
The NEC transmission format consists of the transmission of a leader code, 16-bit custom codes (Custom Code, Custom Code’), and 16-bit data codes (Data Code, Data Code) at one time, as shown below.
Data Code is the inverted code of Data Code.
The leader code consists of a 9-ms carrier waveform and a 4.5-ms OFF waveform and is used as leader for the ensuing code to facilitate reception detection.
Codes use the PPM (Pulse Position Modulation) method, and the signals “1” and “0” are fixed by the interval between pulses.
Remote (REM) output (from stage 2 , transmission occurs only when key is kept depressed)
Magnification of stage 1
Magnification of waveform 3
Magnification of waveform 2
Carrier waveform (Magnification of HIGH period of codes)
Program Flow Chart
Step 1, read and check if the leader code is correct, otherwise initialize check condition and return.
Step 2, read custom and data code, then display.
Timer must be started before checking 0 and 1 code, otherwise, error will be caused.