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  • Ten Daily Electronic Common Sense-Section 118

    What are the simulation steps for the basic application of ModelSim?

    • The simulation steps of the basic application of ModelSim are divided into the following five steps:
      1. Build the library
      2. Build the library
      3. Compile the source code, including all HDL codes and Testbench
      4. Start the simulator and load the top layer of the design
      5. Execute the simulation

    There are big differences between the underwater acoustic sensor network and the traditional wireless sensor network. What are the main aspects?

    1. The UWSN node signal is considered to be irregular due to the differential influence of underwater obstacles, antenna direction, transmit power, antenna gain, battery status, and signal-to-noise ratio threshold. That is, the communication range and perception range of UWSN nodes are irregular in different orientations.
    2. Electromagnetic waves will rapidly attenuate in water and produce multipath effects, while light waves will reflect, refract and scatter. Therefore, they are not suitable for long-distance transmission in water, and UWSN uses acoustic wave communication. Therefore, the propagation delay is much greater than that of electromagnetic waves (the speed of light is about 200,000 times the speed of sound).
    3. The bandwidth of the underwater acoustic communication link is limited, and the transmission bit error rate is high.
    4. UWSN nodes are susceptible to movement due to various external forces (such as water movement, water disturbance, underwater biological contact, etc.).
    5. Due to the harsh underwater environment, nodes are more vulnerable to damage. As a result, the network topology changes frequently and the probability of partial network failure increases.
    6. Underwater acoustic wave modulation and demodulation requires more energy consumption, and the energy consumption of sending underwater messages is much higher than that of receiving messages.

    What are the key points of the rectifier circuit analysis?

    Mainly use the unidirectional conduction characteristic of the diode. Only when the voltage on the positive pole of the diode is greater than the voltage on the negative pole, the diode is turned on, otherwise the diode is in the off state.
    The voltage input to the rectifier circuit is an AC voltage. When analyzing the circuit, the AC input voltage should be divided into positive half cycle and negative half cycle.
    The rectifier diode is forward biased (diode on) or reverse biased (diode off) by using the voltage of the AC voltage itself, which is a characteristic of the rectifier circuit. the
    If one half cycle of the input AC voltage applies a forward bias voltage to the diode, then the other half cycle of the input AC voltage applies a reverse bias voltage to the diode.

    Inductor application:

    Assume the coil is 2 meters in diameter and contains five or six wire loops. You carve grooves in a road and place the coil in the grooves. Put an inductance meter on the coil and see what the inductance of the coil is. Then you can park a car over the coil and measure the inductance again. The inductance will be much greater because there is a bulky steel object placed in the loop’s magnetic field. The car parked on the coil is equivalent to the core of the inductor, and its existence changes the inductance of the coil.
    Most traffic light sensors use this type of loop. Sensors constantly test the inductance of loops in the road. When the inductance goes up, it knows there’s a car waiting! Typically you will use much smaller coils than this.
    An important use of inductors is to work with capacitors to create an oscillator.


    What is the detection method of the Hall-type wheel speed sensor?

    1. Turn off the ignition switch.
    2. Put up the car so that the four tires are about 10om off the ground.
    3. Unplug the wire connector plug of the wheel speed sensor, and connect the wire harness plug to the power terminal of the wheel speed sensor plug with a wire.
    4. Connect the two test leads of the multimeter (with AC voltage gear) to the signal output terminals of the wheel speed sensor (note the positive and negative polarity), and measure the output voltage of the sensor.
    5. Turn on the ignition switch, turn the wheel by hand, the multimeter should display the fluctuating AC voltage in the range of 7~14V. If the voltage is not within the specified range, check the gap between the sensor and the ring gear, the standard value is O. 2 ~ 0.5mm, otherwise it should be adjusted.

    What are the advantages of photodiodes?

    Photodiodes have the characteristics of fast response, small size, low price, solid and durable, and are widely used.

    What is a thermocouple protection device?

    The protection device for the thermocouple is called a protective sleeve, which prevents the hot electrode from directly contacting the measured medium. It can prevent or reduce the erosion and radiation of flame and airflow, so as to ensure a long service life.

    What are the common ARM processor series?

    ARM Company has developed many series of ARM processor cores, the most widely used ones are ARM7 series, ARM9 series, ARMl0 series, ARMll series, Intel’s XScale series and MPCore series. There is also the latest Cortex-M3 series aimed at the low-end 8-bit MCU market, which has the performance of a 32-bit CPU and the price of an 8-bit MCU.

    What are the characteristics of the thermistor?

    There are two types of thermistors, positive temperature coefficient thermistor and negative temperature coefficient thermistor.

    How to detect capacitors?

    1. Detection of fixed capacitors. A detects small capacitances below 10pF. Because the capacitance of the fixed capacitor below 10pF is too small, it can only be checked qualitatively if there is leakage, internal short circuit or breakdown phenomenon by using a multimeter to measure it. When measuring, you can choose the R×10k block of the multimeter, and use the two test leads to connect the two pins of the capacitor arbitrarily, and the resistance should be infinite. If the measured resistance value (the pointer swings to the right) is zero, it means that the capacitor is damaged by leakage or internal breakdown. B Detect whether the 10PF~0?01μF fixed capacitor is charged, and then judge whether it is good or bad. The multimeter selects the R×1k block. The β values ​​of the two triodes are both above 100, and the penetration current should be small. 3DG6 and other types of silicon transistors can be used to form composite tubes. The red and black test leads of the multimeter are respectively connected to the emitter e and collector c of the composite tube. Due to the amplification effect of the composite triode, the charging and discharging process of the measured capacitor is amplified, and the pendulum of the pointer of the multimeter is increased, which is convenient for observation. It should be noted that during the test operation, especially when measuring a capacitor with a small capacity, it is necessary to repeatedly switch the pins of the capacitor under test to touch points A and B, so that the swing of the pointer of the multimeter can be clearly seen. C? For fixed capacitance above 0?01μF, you can use the R×10k block of the multimeter to directly test whether the capacitor has a charging process and whether there is an internal short circuit or leakage, and the capacity of the capacitor can be estimated according to the amplitude of the pointer swinging to the right.
    2. Detection of electrolytic capacitors A Because the capacity of electrolytic capacitors is much larger than that of ordinary fixed capacitors, when measuring, an appropriate range should be selected for different capacities. According to experience, in general, the capacitance between 1 and 47μF can be measured with R×1k gear, and the capacitance larger than 47μF can be measured with R×100 gear. B Connect the red test lead of the multimeter to the negative pole, and the black test lead to the positive pole. At the moment of first contact, the pointer of the multimeter deflects to the right with a large deflection (for the same electrical barrier, the larger the capacity, the larger the swing), and then gradually turns to the left until it stops at a certain position. The resistance at this time is the forward leakage resistance of the electrolytic capacitor, which is slightly larger than the reverse leakage resistance. Practical use experience shows that the leakage resistance of electrolytic capacitors should generally be above several hundred kΩ, otherwise, it will not work normally. In the test, if there is no charging phenomenon in the forward and reverse directions, that is, the hands of the watch do not move, it means that the capacity has disappeared or the internal circuit is broken. If the measured resistance value is very small or zero, it means that the capacitor has a large leakage or has been damaged by breakdown and can no longer be used. C For electrolytic capacitors with unknown positive and negative signs, the above method of measuring leakage resistance can be used to identify them. That is, first randomly measure the leakage resistance, remember its size, and then exchange the test leads to measure a resistance value. The one with the larger resistance value in the two measurements is the positive connection method, that is, the black test lead is connected to the positive pole, and the red test lead is connected to the negative pole. D Use a multimeter to block electricity, use the method of positive and negative charging to the electrolytic capacitor, and estimate the capacity of the electrolytic capacitor according to the size of the pointer swinging to the right.
    3. Inspection of variable capacitors A. Gently rotate the rotating shaft by hand, it should feel very smooth, and should not feel loose or tight or even stuck. When the loading shaft is pushed forward, backward, up, down, left, right, etc., the shaft should not be loose. B Use one hand to rotate the rotating shaft, and the other hand to lightly touch the outer edge of the moving plate group, and there should be no looseness. A variable capacitor with poor contact between the rotating shaft and the moving piece cannot be used any longer. C Put the multimeter in the R×10k block, and connect the two test leads to the leading end of the moving piece and the fixed piece of the variable capacitor with one hand; slowly rotate the rotating shaft a few times with the other hand, and the pointer of the multimeter should be Do not move at infinity. In the process of rotating the shaft, if the pointer sometimes points to zero, it means that there is a short circuit point between the moving piece and the fixed piece. If it encounters a certain angle, the reading of the multimeter is not infinite but a certain resistance value appears, indicating that there is leakage between the moving piece and the fixed piece of the variable capacitor.


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