Keywords: FM receiver, audio monitoring device
Frequency modulation receiver of load frequency, audio monitoring device
Author: Shandong Lang Yong Han Zhao training Feng Wei
In order to send the wireless frequency modulation program content, it is highly sent out, except for high quality, high-performance launch devices. The signal of the transmitted program should also be listened at any time. When the multi-set FM program simultaneously sends, it is difficult to listen to each set of programs. In order to monitor the signal source and the running state of the transmitter, we have installed it in listening to the FM receiver. Terminal, audio monitoring device.
No carrier monitoring range: After the transmitter, the transmitter has caused the transmitter to remove high pressure no power output; the power supply, power amplifier, control device of the exciter fail, resulting in no output of the exciter; the last front stage 100W power amplifier and power failure Resulting in 100W no power output: or the end-level high-power electronic pipe amplifier power supply fault, exhaustiation, and electronic pipe damage result in no power output, this monitoring device can immediately issue alarm.
No sound monitoring range: There is a problem with this station signal source, resulting in no audio signal output of the transmitter; the actuator audio processor, the audio amplifier fault, no modulation signal output. Leading the transmitter without audio, no carrier frequency signal output; the transmitter equipment is normal. The audio signal is stopped at the front or center table, resulting in no audio signal output of the transmitter; this monitoring device is delayed after the audio signal is interrupted for 25 seconds.
Each program receiver is installed in a set of monitoring devices. With different music integrated blocks, the FM receiver can make different alarm sounds. The alarm music integrated block market is available, or you can use the music blocks in children's toys. Circuit schematic is shown in the drawings.
Monitoring device principle composition: The monitoring device consists of + 5V operating power, carrier sampling, audio sampling, NE555 and monitoring device sound source circuits. NE555 8 foot link + 5V power supply VCC; 1 foot ground; 2 foot is set end, when level ≤ 1 / 3VDD (around 1.7V).
3 foot output high (4 foot is high), 4 foot is strong reset, when level ≤ 1.4V, no matter how 2 foot, 6 foot level, 3 foot output is low. 5 Insert 0.01-0.1 μF capacitance to the ground, prevent interference. 6 Feet is a reset, when level ≥ 2 / 3VDD, while ensuring 2 foot ≥ 1 / 3VCC, 3 foot output is low. 7 pin is the discharge end. The NE555 changes the output end by accepting a variation of the sampling level, thereby triggering the sound source circuit and alarm. The audio interruption is determined by the charging time constant of R4 and C7, and the delay time is approximately 1.1RC (s), and the value of the RC can be changed to change the delay time. Here R4 = 220kΩ, C7 = 100 μF delay time is about 25 seconds, due to intermittent stop due to the audio signal; if time setting is short, it is easy to cause false alarm.
The monitoring device is powered by the Vicalcup receiver 9V power supply. In order to ensure the accuracy of the monitoring device, the monitoring device is used to increase the primary regulator isolation between the power supply of the monitoring device and the receiver, that is, the + 9V power source is used by the 7805 regulator output + 5V voltage for alarm. The carrier frequency signal is from the receiver tuning indication, or takes the receiver carrier voltage variation point.
When the transmitting machine carries, after receiving this emission frequency. The tuning indicator is on, and the positive electrode voltage of the luminous tube is about + 5.5V, and the negative electrode voltage is about + 3.7. The light-emitting tube is conductive while transmitting the optical coupling 4N25 (N1) input. The power supply + 5V voltage is added to the NE555 4 foot for strong reset, and R2 is a current limiting resistor, and the 3 foot output is high. The 5V voltage of the 3 foot of the NE555 causes the optical coupling 4N25 (N4) input to the input. The optocoupler output is low, then the voltage of the sound source integrated block trigger is low (0V), and the sound source integrated block Y does not trigger, and does not post alarm signal.
When there is no power output or high pressure without the power output or high pressure, the light-emitting diode negative electrode potential of the receiver tuning indicated (the measured tuning exhaust pipe negative electrode voltage is 8.8V, the positive electrode is still 5.5V), resulting in the illumination tube Do not illuminate. At the same time, the optical coupling 4N25 input is closed.
The 4 feet of the NE555 becomes low, and the 3 foot level turns to low levels to make the input of the optocoupler N4 are also closed, and the output terminal is changed to high, and the voltage of the sound source integrated block trigger is changed to high electricity. Flat (1.9V), the alarm indicator D3 is on, and the source integrated block Y issues alarm signal. The source circuit voltage is between 1.5 to 4.5V, and the trigger voltage is determined by the alarm indicator D3 (red) on the threshold, and the D3 is automatically extinguished after troubleshooting.
The audio signal is terminated by the receiver unbalanced audio output to the ground end of the outermost capacitor C3 positive, the outer skin connection alarm. The transmitter is audio amplification by V1 under normal operation. The multiplication stream is added to D1, D2, C6 by the acoustic capacitor C5, and the control sensitivity potentiometer RP1 is adjusted, so that the B point voltage is about 0.6V. Ensure that the V2 is turned on, so that the collector C point voltage is 0V, and the 3 foot output of NE555 is high, ensuring that N4 is in turn, so that the output voltage is low, and the sound source integrated block does not supply and trigger the voltage. The monitoring device does not alarm, indicating that the audio signal is normal.
When the transmitting machine carrier frequency outputs, no audio signal, including the front station signal interrupt, the inside signal source interrupt and transmitter actuator audio processing, audio amplification is faulty, resulting in no modulation signal input, or input The audio signal is very small, the monitoring device audio is unveiled, the no audio output is unveiled on the B point, resulting in the V2 turn-off, and the C point level is charged by the + .5V power supply via R4 to C7, when charge 2 / 3VDD ( That is, when 3.4V is left.), The NE555 is turned low, and N4 is turned on, and the sound source integrated block starts alarm. After the alarm is completed, after the fault is released. D3 is automatically extinguished, the monitoring device re-enters the monitoring state.
The alarm uses debugging: Monitor circuit installation, after the check is correct, disconnect the audio sample signal. Measure the audio amplifier DC operating point, adjust the potentiometer RP2. Make the voltage of the A / 2VDD (about 2.5V). Add the audio sampling signal, adjust the potentiometer: RP2 makes the voltage of the B point close to 0V; then remove the audio sample signal, after delay in 25 seconds, the monitoring device starts alarm, when the audio signal is recovered, the alarm indicator D3 will Immediately extinguish, if D3 is still not extinguished. The re-tuning RP1 causes the B point electricity to a 0.6V conduction voltage. After debugging, the monitoring device can be put into operation.
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