Design and production of satellite receiver crash recovery circuit

The circuit cuts off the power supply of the receiver and then powers it on again, so that the satellite receiver automatically resumes normal operation. The entire process does not require human intervention.

1. Circuit Analysis

The circuit is shown in the figure below. The whole circuit consists of two parts: audio signal processing circuit and power-off restart circuit. The circuit has a simple structure and high working reliability.

1. Audio signal processing circuit

The audio signal processing circuit is composed of dual operational amplifier LM358, time base circuit 555, etc. Its function is to detect whether the satellite receiver has audio signal output, that is, whether it is frozen, and output corresponding high and low level signals to the power-off restart circuit to control its operation.

(1) When the audio signal is normal, N1 is a single-power dual op amp LM358. NIA is connected as an inverting amplifier to prevent the common-phase amplifier from outputting a high level when there is no audio signal (the input terminal is open), which affects the normal operation of the subsequent circuit. Adjusting R2 can change the gain of NIA to ensure that the audio signal amplitude is large enough. The audio signal amplified by NIA is rectified and filtered by D1 and Cl, and then sent to the positive end of NIB. Since the voltage at the positive end of NIB is higher than that at the negative end, NIB outputs a high level, D2 is turned on, N2's ② and ⑥ pins are high, and its ③ pin outputs a low level, indicating that the audio signal is normal.

(2) When there is no audio signal, there is no signal input to NIA. The voltage sent to the positive terminal of NIB after rectification and filtering by D1 and Cl is lower than the voltage at the negative terminal. NIB outputs a low level and D2 is cut off. At this time, the voltage of N2 pins ② and ⑥ will not drop immediately.

C2 is charged slowly through R6, and the voltage of N2's ② and ⑥ pins gradually decreases. N2's ③ pin has a delay time to maintain a low level until the voltage of ② and ⑥ pins is lower than 2/3VCC, then N2 flips and its ③ pin outputs a high level. If there is an audio signal input during the delay time when N2's ③ pin maintains a low level, N2's ③ pin will always maintain a low level, that is, there will be no change from low to high level, thus preventing malfunctions caused by pauses and intervals between programs.

2. Crash recovery circuit

The crash recovery circuit is composed of CD4093, delay time circuit and electronic switch. When the audio signal is normal, the low level output from pin ③ of N2 is sent to pins ① and ② of N3A through R7, and then outputs a low level after being inverted by N3A and N3B, making transistor Tl cut off; it is sent to N3C (12) and outputs a high level after being inverted by N3C, and then charges C4 through D3 and R8, making N3D ⑧ and ⑨ pins high-level pins. Because the outputs of N3B and N3D are low-level, N4B outputs a high level, and charges C5 through D4 and R2, making N4C ⑧ and ⑨ pins input high level, and its ⑩ pin outputs a low level, making T3 in the cut-off state, that is, at this time, pin (13) of N3C is in the high-level state. Since Tl is in the cut-off state at this time, relay K1 does not work, and the satellite receiver maintains normal working state.

When the audio signal is interrupted for a long enough time, so that the N2 pin ③ outputs a high level, N3B outputs a high level, and T1 is turned on. Due to the effect of C4, T2 is still in the on state at this time, the relay K1 coil is energized, and its normally closed contact is disconnected, causing the satellite receiver to stop working due to power failure.

At this time, the (12) pin of N3C is also high level, and the (13) pin is high level because T3 is cut off. Its 9th pin outputs low level, the diode D3 is cut off, C4 discharges through R9, and the voltage of the 8th and 9th pins of N3D slowly decreases. The discharge time of C4 determines the length of time the satellite receiver is turned off. When the voltage on C4 drops to the lower limit of the low level of N3, N3D outputs high level, T2 is cut off, the coil of relay K1 is de-energized, its normally closed contact is connected, and the satellite receiver is powered on again. At this time, N3B and N3D both output high level, N4B outputs low level, and D4 is cut off. C5 discharges through R13. This discharge time determines the time from restarting to shutting down again for the satellite receiver. This time must be greater than the time required for the satellite receiver to start up and lock the satellite signal, otherwise the receiver cannot be started, that is, it has not entered the normal working state (no audio signal output), and the power is turned off again. As C5 discharges, the voltages at the ⑧ and ⑨ pins of N4C gradually decrease, eventually causing N4C to output a high level, turning on transistor T3. The N3C (13) pin becomes a low level, and N3C outputs a high level. Through D3, N3D inputs a high level and outputs a low level, turning on T2. ​​Since T1 is turned on at this time, the normally closed contact of relay K1 is disconnected again, and the satellite receiver is powered off again...

If the audio signal is abnormal, this state will continue to cycle. At the same time, the high and low level change signals output by N4B4 pin serve as the clock signal of N5 to control N5 to complete subsequent work. Once the audio signal returns to normal, the above cycle will end immediately, the satellite receiver will be locked in the working state, and subsequent processing will stop.

N5 is a dual serial input and parallel output shift register CD4015, and this circuit uses half of it. RST is the reset terminal, which is valid at a high level. CLK is the clock signal control terminal, which is triggered by the rising edge. When the D terminal is at a high level, a clock signal comes, QO outputs a high level, and another clock signal comes, Ql outputs a high level, and so on. After the crash processing circuit cycles twice, another clock signal comes, Q2 outputs a high level, T4 is turned on, and the buzzer alarms, reminding the on-duty personnel to check the machine equipment and take corresponding measures. When the next clock pulse arrives, Q3 is at a high level, and N5 is cleared through D6 and C6. No matter what state N5 is working in, as long as the audio signal is normal, N2 pin ③ outputs a low level, which is inverted by N4A, giving a high level to the N5 RST terminal, and immediately clearing N5. The diodes D6 and D7 play an isolation role. SB is a manual reset button. Press the SB button lightly, and the N5 output is immediately cleared. C7 is used to clear N5 when the machine is powered on.

The power supply circuit is relatively simple. 220V AC is stepped down by the transformer, rectified by QD, filtered by capacitors C8 and C9, stabilized by LM7812 and LM7806, and outputs two sets of DC voltages +12V and +6V. +6V powers N3 and N4, and +12V powers other circuits. D8 is used as a power indicator. Cl0 is a high-frequency filter capacitor.

2. Circuit Adjustment

1. Adjustment of audio processing circuit

For debugging purposes, the audio output of the radio can be used as the input audio signal. Connect the audio input signal to the left end of resistor R1. When there is no audio signal, adjust R5 to make the voltage of NIB pin 6 higher than that of pin 5, and make the voltage of pin 5 higher than that of pin 6 when there is an audio signal. Adjust R6 to make the delay time when there is no audio signal input slightly longer than the longest pause and interval between programs, usually not less than 5 seconds. Use a multimeter to measure N2 pin 3. When there is an audio signal, it is low frequency, and when there is no audio signal (i.e., the machine is frozen), it is high level.

2. Adjustment of the crash recovery circuit

Mainly adjust two delay times:

(1) Adjust the power-off time of the satellite receiver, that is, adjust R9 and C4 so that the power-off time is about 10s.

(2) Adjust the time from satellite receiver restarting to satellite signal locking. Adjust C5 and R13 so that the delay time meets the time required to lock the satellite signal.

To facilitate observation and timing during adjustment, you can first connect a light bulb to the contact of relay K1 to replace the satellite receiver. After it works normally, connect the satellite receiver for further adjustment until it fully meets the requirements.

The resistor used in this circuit is 1/8W, and the transistor can be replaced by other types. As long as the welding is correct, the circuit can be used normally after simple adjustment, and the work is stable and reliable.