Working Principle and Application of LM567 Universal Tone Decoder Integrated Circuit

Working Principle and Application of LM567 Universal Tone Decoder Integrated Circuit

The 567 is a universal tone decoder that provides a saturated transistor to ground switch when the input signal is within the passband. The circuit consists of I and Q detectors, and the oscillator is driven by a voltage-controlled oscillator to determine the decoder center frequency. The center frequency bandwidth and output delay are independently set using external components.

Mainly used in oscillation, modulation, demodulation, and remote control encoding and decoding circuits, such as power line carrier communication, intercom sub-audio decoding, remote control, etc.

20 to 1 frequency range with external resistor
Logic compatible output with 100mA current absorption capability.
Adjustable bandwidth from 0% to 14%
Wide signal output with high noise suppression
Anti-interference to false signals
Highly stable center frequency
Center frequency adjustment from 0.01Hz to 500kHz
Power supply voltage 5V--15V, 8V is recommended.
Application example: 104 capacitor connected to input terminal, 10K pull-up resistor connected to output terminal, C1 and C2 are 1uF. R1 and C1 determine the oscillation frequency, generally C1 is 104 capacitor, R1 is 10K--200K. The power supply voltage is 8V.

Single-channel infrared remote control circuit
In applications where multi-channel control is not required, a single-channel infrared remote control circuit composed of conventional integrated circuits can be used. This remote control circuit does not require the use of expensive dedicated encoders and decoders, so the cost is low.
The single-channel infrared remote control transmitter circuit is shown in Figure 1. A high-speed CMOS quadruple two-input "NAND" gate 74HC00 is used in the transmitter circuit. Among them, "NAND" gates 3 and 4 form a carrier oscillator, and the oscillation frequency f0 is adjusted to about 38kHz; "NAND" gates 1 and 2 form a low-frequency oscillator, and the oscillation frequency f1 does not need to be accurately adjusted. f1 modulates f0, so the waveform output from "NAND" gate 4 is an intermittent carrier, which is also the waveform transmitted by the infrared light-emitting diode. The waveforms of several key points are shown in Figure 2. The B' waveform in the figure is the waveform output at point B when point A is not modulated but directly connected to a high level. It can be seen from Figure 2 that when the waveform at point A is at a high level, the infrared light-emitting diode transmits a carrier; when the waveform at point A is at a low level, the infrared light-emitting diode does not transmit a carrier. The frequency of this stop and shoot is the low-frequency oscillator frequency f1. Why don't we use the cheap, low-speed CMOS quadruple two-input "NAND" gate CD4011 in the infrared transmitter circuit, but use the more expensive 74HC00? It is mainly due to the limitation of the power supply voltage. There are many kinds of infrared transmitter shells, but the power supply is generally designed to be 3V, using two No. 5 or No. 7 batteries as the power supply. Although the nominal operating voltage of CD4011 is 3~18V, it is for processing digital signals. Because the CMOS "NAND" gate here is used to oscillate and generate square wave signals, that is, analog applications, its operating voltage must be at least 4.5V, otherwise it is not easy to oscillate, affecting its use. The minimum operating voltage of the 74HC series CMOS digital integrated circuit is 2V, so using a 3V power supply is "handy". The pin functions of 74HC00 are shown in Figure 3.

Figure 4 is an infrared receiver demodulation control circuit. In the figure, IC1 is LM567. LM567 is a phase-locked loop circuit, which adopts 8-pin dual in-line plastic package. The external resistors and capacitors of its ⑤ and ⑥ pins determine the center frequency f2 of the internal voltage-controlled oscillator, f2≈1/1.1RC. Its ① and ② pins are usually grounded through a capacitor to form an output filter network and a loop single-stage low-pass filter network. The capacitor connected to the ② pin determines the capture bandwidth of the phase-locked loop: the larger the capacitance value, the narrower the loop bandwidth. The capacitance of the capacitor connected to the ① pin should be at least twice that of the capacitor of the ② pin. The ③ pin is the input terminal, and the input signal is required to be ≥25mV. The ⑧ pin is the logic output terminal, which is an open collector transistor inside, and the maximum sink current allowed is 100mA. The operating voltage of LM567 is 4.75~9V, the operating frequency is from DC to 500kHz, and the static operating current is about 8mA. The internal circuit and detailed working process of LM567 are very complicated. Here we only summarize its basic functions as follows: When the LM567's ③ pin inputs a signal with an amplitude ≥ 25mV and a frequency within its bandwidth, the ⑧ pin changes from a high level to a low level, and the ② pin outputs a modulated signal after frequency/voltage conversion; if an audio signal is input to the device's ② pin, the ⑤ pin outputs a frequency-modulated square wave signal modulated by the modulation signal input to the ② pin. In the circuit of Figure 4, we only use the characteristic that the voltage of the ⑧ pin changes from high to low after the LM567 receives a carrier signal of the same frequency to form control over the control object.

After clarifying the basic working principle and function of the LM567, it is very simple to analyze the circuit of Figure 4. IC1 is an infrared receiver, which receives the infrared signal sent by the transmitter, and its center frequency is the same as the transmitter carrier frequency f0. After demodulation by IC1, a square wave signal with a frequency of f1 is output at the output terminal OUT, which is the same signal as the waveform at point A in Figure 1. We adjust the center frequency of LM567 to the same oscillation frequency as the "NAND" gates 1 and 2 in the transmitter, even if f2 = f1. Then when the transmitter transmits a signal, LM567 starts to work, and the ⑧ pin changes from a high level to a low level. This changing level can be used to control various objects. Using the circuit in Figure 4, we can make a remote control switch to remotely control various household appliances at home.
In fact, using the circuits shown in Figures 1 and 4, we can also easily transform it into a multi-channel remote control circuit. The method is: in the transmitter (Figure 1), the resistor R* is changed to several different values, thereby forming several modulation signals with different frequencies; in the receiving circuit, several LM567s are set, and their inputs all come from the infrared receiving head. The oscillation frequency of each LM567 is different but corresponds to the transmitting end one by one. In this way, when the transmitter presses different buttons and connects to different modulation signals, the level of the ⑧ pin of the corresponding LM567 at the receiving end will change, thereby forming multi-channel control. Strictly speaking, this is a kind of frequency division multiplexing. Compared with digital encoding and decoding multi-channel control, the disadvantage is that the debugging is more complicated. But in some occasions, such as in multi-channel alarm, it also has a place. Because in alarm applications, when it is necessary to solve the problem of more than two channels of alarm at the same time, time division multiplexing will cause complex synchronization problems, which can be easily solved by frequency division multiplexing if the bandwidth allows.

Ultrasonic remote control circuit
1. Ultrasonic remote control light switch
This remote control switch has a simple circuit and does not require debugging, making it very suitable for beginners.
1. Working principle
It is a transmitting circuit. The circuit is composed of discrete devices. VT1 and VT2 and R1~R4, C1, and C2 form a self-excited multivibrator. The ultrasonic transmitting device B is connected to the collector loop of VT1 and VT2 and works in a push-pull form. The loop time is often determined by R1, C1 and R4, C2. The resonant frequency of the ultrasonic transmitting device B triggers the multivibrator circuit. Therefore, this circuit can work at the optimal frequency.

(Figure 2) is the receiving circuit. The junction field effect VT1 constitutes a high input impedance amplifier, which can be well matched with the ultrasonic receiving device B, and can obtain higher receiving sensitivity and frequency selection characteristics. VT1 adopts a self-supplied bias mode. Changing R3 can change the state working point of VT1. The ultrasonic receiving device B converts the received ultrasonic wave into a corresponding electrical signal. After being amplified by VT1 and VT2, it is half-wave rectified by VD1 and VD2 to become a DC signal. After being integrated by C3, it acts on VT3 and the base, making VT3 turn from cut-off to conduction, and its collector outputs a negative pulse. The trigger JK triggers D to flip it. The level of the Q end of the JK trigger directly drives the relay K, making K attract or release. The contact of the relay K controls the switch of the circuit.

2. Component Selection
In the transmitting circuit, VT1 and VT2 use low-power transistors such as CS9013 or CS9014, ≥100. The ultrasonic transmitting device uses SE05-40T, and the power supply GB uses a 9V laminated battery to reduce the size and weight of the transmitter.
In the receiving circuit, VT1 and 3DJ6 or 3DJ7 and other low-power junction field effect transistors. VT2~ VT3 use CS9013, ≥100. VD1 and VD2 use IN4148. JK trigger 263B. The ultrasonic receiving device uses SE05-40R, which is used in pairs with SE05-40T. Relay K uses HG4310.

Ultrasonic remote control fan transmission
1. Working principle
(Figure 3) is the transmitting circuit. It uses the domestic Bat brand FS-A5A electric fan remote control transmitter. This transmitter has the characteristics of small size, low power consumption, reliable operation, and simple circuit. When in use, each time the transmitter key is pressed, the transmitter emits a 40KHZ ultrasonic wave of about 500ms. The working principle of the transmitting circuit is as follows.

VT2 and VT3 form a direct coupled positive feedback oscillation circuit, B is a 40KHz ultrasonic transmitting device, and also serves as the oscillation circuit feedback frequency element. Therefore, this circuit can accurately oscillate at the center frequency of the ultrasonic transmitting device 40KHZ. VT1, R2, and C1 form a 500ms delay circuit. R1 and VD1 are the discharge path of C1. When the transmitting key S is pressed, the oscillation circuit formed by VT2 works and emits ultrasonic waves. At the same time, the power supply charges C1 through R2. When the potential on C1 is charged to 1.4V (about 500ms), VT1 is turned on, the potential of VT2 base and VT3 collector drops to about 0.3V, and the oscillator stops working. When the transmitting key S is released, C1 is quickly discharged through VD1 and R1 to prepare for the next transmission. VD3 and R4 form a transmission indication circuit. When the transmitting key is pressed, VD3 emits light.
(Figure 4) is the receiving circuit. CMOS NOT gates D1~D3 are biased as linear amplifiers by R1, and the total gain can reach more than 60bB. Due to the high input impedance of the CMOS circuit, it can be well matched with the ultrasonic receiving device. The amplified signal is coupled to the input terminal 3 pin of the phase-locked loop decoder LM567 by C1. When the frequency of the input signal falls on its center frequency, the logic output terminal 8 pin of LM567 changes from high level to low level.

Frequency-selective voice-controlled switch
This voice-controlled switch can control the on or off of any electrical appliance by a sound of a specific tone (500 to 2000Hz). Since it has a certain frequency-selective function, the probability of false operation is small.
The circuit is designed to be controlled by an audio signal (up to 100mV). The control signal source can be a telephone, a radio, a record player, or a tape recorder, and is drawn from an appropriate point with a shielded wire. If you want to use sound wave remote control, add an electret microphone and a first-level preamplifier.
The circuit of this device is shown in Figure 16. Its central component is a pickup integrated circuit LM567 and a 50mA relay.
After an audio signal of a certain tone is added to the input terminal (pin 3) of LM567, it is processed by the internal circuit amplification, frequency selection, etc., and outputs a low level at its output terminal 8 pin (high level when there is no input signal). At this time, a PNP tube (2N3906) connected to it is turned on, causing the relay connected to the collector circuit to be attracted, thereby controlling the controlled electrical appliance with its contacts. If it is used to turn on the machine, the normally open and normally closed contacts of the relay should be used; if it is used to
shut down the machine, the normally closed and normally open contacts should be used. The response frequency is determined by the value of the potentiometer and capacitor connected to the 5th and 6th pins, so adjusting the 10kΩ potentiometer can adjust its response frequency. The audio range that this machine can receive is 500~2000Hz.
The diode 1N4001 is used to protect the crystal triode. 2N3906 can be replaced by any other type of medium and small power PNP silicon tube.