Single channel infrared remote control transmitter circuit bc

In applications that do not require multi-channel control, a single-channel infrared remote control circuit composed of conventional integrated circuits can be used. This kind of remote control circuit
does not require the use of a higher-priced dedicated codec, so the cost is lower.
    The single-channel infrared remote control transmitting circuit is shown in Figure 18-56La. A high-speed CMOS quadruple two-input NAND gate 74HCOO is used in the transmitter circuit
. Among them, "NAND" gate 1, gate 2 and other components form a low-frequency oscillator, the oscillation frequency is f, gates 3 and 4 form a carrier
oscillator, the oscillation frequency is adjusted around 38kHz; the oscillation frequency fi does not need to be accurately adjusted, l is correct fo is modulated, so the waveform output from the NAND
gate 4 is an intermittent carrier wave, which is the waveform transmitted through the infrared light-emitting diode.
    The waveforms of several key points are shown in Figure 18-56b. The Br waveform in the figure is the waveform output by point B when point A is directly connected to a high level without modulating the waveform
. It can be seen from Figure 18-56b that when the waveform at point A is high level, the infrared light-emitting diode emits a carrier wave} when the waveform at point A is low level
, the infrared light-emitting diode does not emit a carrier wave . This frequency of stopping and firing is the frequency of the low-frequency oscillator^. In the selection of components in the infrared emission circuit
, the low-priced low-speed CMOS quadruple two-input NAND gate CD4011 is not used, but the higher-priced 74Hcoo is used. The main reason
is due to the limitation of the power supply voltage. There are various shells of infrared transmitters, but the power supply is generally designed to be 3V, using two AA or AA
batteries as the power supply. The standard operating voltage of CD4011 is 3~18V, but for processing digital signals, the operating voltage for oscillating the oscillation circuit to generate a square wave signal
must be greater than 4.5V, otherwise it will be difficult to oscillate and affect use. The lowest operating voltage of the CMOS digital integrated circuit of the 74HCOO series
is zv, so it is more convenient to use a 3V power supply for the transmitter.