"Pocket Wireless Microphone, Wireless MicroPhone
Keywords: pocket wireless microphone
Pocket "QIE-listener" wireless microphone
Warning: This circuit is for reference only, please do not use for illegal purposes.
Pocket transmitter, very suitable for beginners, simple circuit is simple and easy, low cost, no output power is not more than 5-8MW, the launch range can be 300 meters to 300 meters here, I'm a pocket transmitter introduced, very suitable for beginners Simple and easy to circuit, low cost, no output power is not more than 5-8MW, the launch range can be around 300 meters, with a common FM radio, showing its sensitivity and clarity, the most The challenging part is to have such launching capabilities only with 3V power and half-wave antennas. In addition, because the parts required for the circuit are less, it can be placed in a matchbox (larger than the domestic - all match box), as the -QIE-listener, can be said that God does not know, the ghost, but It is not limited to this aspect, which can be placed in the baby room, gate or corridor channel, monitoring the actual situation, and can also be used as a night security device. The current loss of the circuit is less than 5 mA, and two dry batteries can be used to work between 80 and 100 hours. The circuit is very stable under normal operation, the frequency drift is very small, the test: After 8 hours, no need to recover again. The only thing affecting the output frequency is the condition of the battery. When the battery is aging, the frequency is slightly changed. With this production, learn about FM transmission, you can understand its superior place, especially it produces no noise, even if it is transmitted, it is also easy to achieve well. Circuit Working Principle From Figure (1) Circuit Visit 2, Level 1 Audio Amplifier and 1 RF Oscillator.
There is a FET in the actual microphone in the eternal microphone. If you like, the visual is level, and FET amplifies the capacitance of the microphone precursor membrane, which is the sensitive reason for the eradicacy. The audio amplifying is carried out by its emitter crystalis Q1, the gain is about 20 to 50, and the amplified signal to the oscillator level Q2 is operated at a frequency of about 88 MHz, which is a oscillation coil (a total of 5 laps. ) And 47PF capacitor adjustments, this frequency is also determined in transistors, 18pf back-activators, and there are also a few biasing elements, such as a 470 Ω emitter resistor, and a 22K base resistance. When the power is turned on, the 1NF base capacitor is gradually charged by 22K resistance, and 18 pf is charged with 470 Ω resistance of oscillating coil, but is more fast, and the 47PF capacitor is also charged (although only two ends of the two ends), the coil generates a magnetic field. . When the base voltage gradually increases, the transistor is turned on and effectively connects the internal resistance and connected to both sides of 18pf. When the 1nf capacitor is charged to the working voltage of the pole, several messy week waves have occurred, so we assume that the discussion is approaching the working voltage. The base voltage continues to rise, the 18NF capacitor attempts to prevent the movement of the emitter from being moved, and when the energy depleted in the capacitor and no block movement, the substance voltage is lowered, the transistor is turned off, and the current of the transistor is also stopped. Magnetic field declaration. Magnetic field declaration, producing a voltage in the opposite direction, the column voltage is reversed from the original 2.9V to exceed. 3V, and in the opposite direction 47PF capacitor charge, this voltage also affects the 18PF capacitor charging, and the voltage on the 470 Ω emitter resistor fuel to the crystal pipe into a deeper turn-off. When the 18PF capacitor is charged, the radiation voltage has fallen and falls to a crystalist to start turning on, current flows into the coil, and confronts the declaced magnetic field. The voltage on the coil is reversed, forming the collision voltage drop, this change is transmitted to the emitter by 18PF, resulting in a deeper conduction, shorting the 18PF capacitor, and the cycle start repeat. Therefore, Q2 is here to form an oscillation, generate an AC signal of 88MHz. The audio signal after the zoom is collected by 0.1uf capacitor! The base of Q2 changes the oscillation frequency, generates the required FM signal. Before making process, it is best to prepare the printed plate and two batteries in the air, and how many spaces are available in the bottom. Although the vacancy is limited, but still needs to leave a small position to give a matchful match, it can be pasted on the paper jam, and the purpose is to cover the circuit, make people feel that it is just a box of matches, will not be noticed. A Qie-listener. Now put all parts on the work desk, and clear their values by part, then the classification is arranged in order, this is very organized, avoiding the solder distribution. The tin wire is preferably used with special 0.6LMM resin (loose fragrance) tin wire, because of its body, welding is fast and easy to get tin, with 15 to 2 x small electric soldering iron is enough, before use, use sponges to rape Clean, the only thing that must be homemade is the coil, which is required to use a 22nd BS (ф 0.5 mm) or No. 24 BS (фm.71mm) painted copper wire or a copper wire. Wheel around the 3mm diameter coil rack, such as around the medium screwdriver, and then separated from the circle to the circle 5.5 mm. When the final adjustment frequency is adjusted, the output frequency is changed by compressing or elongation of the coil. If your coil is made with a paint package, you must strip the patent leather on the two heads of the line and then onto the tin. The position welding bottom plate can now be placed in accordance with the part of the part (3), first starting from the resistance, follow the capacitance, transistor, coil, and words, the resistance is vertically above the bottom plate, but maintains a height to minimum. The pin of the crystalist should be inserted into the bottom plate, and the height of the tube is not protruded. The two batteries are used with switch welding, and the electrodes are connected to the bottom plate with the line. Finally, use a 10cm long copper wire to connect on the bottom plate "" A "" point, as antenna, the entire manufacturing process is completed, is it? Why do you strange the circuit? How many times after the installed circuit does not work properly? Please don't blame yourself, or you have to break the magazine that teaches you, many times because of the so-called "error". All parts manufactured by the manufacturing plant have their values, but this value is only within "Differences", not the "normal" value of printing on it. This difference is called an error, and if the error is 5%. This means that the actual value of the part is between 5% and above 5% of its marked value. Error often applies to resistors, capacitors, transistors, and other components such as microphones, coils, and integrated circuits. However, there is another factor, referred to as boundaries, each component is in the circuit, and there is a range of values in the case, as long as the value is still within this range, or within these boundaries, the circuit is Appropriate work, when emit each component, it is in the middle of this range. Most circuits are not strict restrictions, such as selecting another higher or lower value from the designated component, usually work well, if not, the circuit is not very strict, the value is not appropriate. When you publish a line through the magazine, there will be a variety of different levels of people, and the parts needed from all sources. Sometimes they use the specified value, sometimes they choose a value. Also, some parts have 1-5% error, while others are 60% of the marked values, when these parameter differences and boundaries are mixed in any way, you encounter the circuit's non-operating. Take the microphone as an example. Under the 3V power supply, some words only need to use 100K load resistance (R1) to have a very good sensitivity, others may need to use only 4.7k to achieve only acceptable sensitivity, from the exterior you can't Say the difference in both, they seem to be, but they are far from the electrical characteristics. It is also applicable to the transistor, and the specification table may illustrate that the two tube characteristics are close to the same, but when they pick up: When the circuit is connected, one work is intentionally, and the other work is out of spirit. Please don't worry that I am afraidless because I have seen the above words, as long as the circuit's requirements are considered, it can be successful. After all parts of the circuit are soldered, it is best to check all the welding points in the naked eye. Is there a fake soldering, or the solder is used to use too much and proximity to short circuits, and it can be used to check and test performance. The test step is to add a short antenna (5 to 10 cm long) to tune the A point of the bottom plate - the part FM radio on the entire band, look for the signal.
It is best to keep the transmitter with the radio to prevent checking to any harmonic or lateral wave. If the radio failed to detect the carrier, the frequency may be too low, slightly eliminating the oscillation coil, and try again. If the coil is rotated with a wiring copper wire, it should be noted that the chart should not be encountered with each other. If a patent leather copper wire is used, it is necessary to know the connectivity of the circle, and the low blockage of the multimeter is used to remove it, or the amount of circuit current should be 4-6 mA. Once checking the carrier, place the QIE-listener to the side of a clock, check the sensitivity of the circuit, the radio should make a clear "" Tip ", the circuit should be more sensitive than your ear . The load resistance (R1) of the microphone determines the sensitivity, which can be reduced to 10K or to 47K, depending on the sensitivity of the required requirements. To determine the frequency of the transmitted, you will leave your local FM broadcast Tuna, because the signal is strong, when you test the distance, you will cover the QIE-listener. The coil is compressed, the frequency is lowered; the length, the frequency increases, so exactly to the fine-tuning capacitor, saves the cost of this machine, but if you like the fine-tuning capacitor. Lishui, C4 is preferably used with a 39PF ceramic capacitor, and another 10pF or 22pf fine-tuning capacitor is connected, so that the circuit can be adjusted more carefully. The coil adjustment is easily deviated from the FM band. In theory, the sensor should also be adjusted to the L / C ratio of the maintenance tuning circuit, but we need to have a small range, so there is no limit. Using a FM receiver with adjustment indicator, it can determine how much the output power of this unit is needed. It is necessary to make a comparison, indicating that the four unit degrees on the table, indicating a very good output, and use 10 cm when testing this unit. Long antenna is placed in horizontal placing, and the harmonic device is 10 meters. With the four unit degrees, it is known to use a half-wave antenna. (170cm long), the unit can be emitted to about 300 meters. What should I do if I don't work? In the FM receiver, the QIE-listener is not received, first, the frequency is determined below the normal 88-108MHzFM band, which is the most likely cause. The current of the circuit is measured. If there is 4-6mA, the representation is working, slightly eliminating the coil, and scans the entire band. When contacting any element on the bottom plate, only one non-metallic screwdriver, and leave the battery Because the capacitive effect caused by the skin in your hand can cause the circuit to be obviously disordered and the output may be completely stopped. Also, it is also important to maintain 3V power supply and close the battery close to the bottom plate. The entire wiring must be as shown in Figure (2), and once the same circuit distribution capacitor is maintained, the circuit can be changed, but in the initial test step, each component must be placed in the foot chart.
The oscillator works in about 88MHz unless you have a 100MHz oscilloscope, it is difficult to see its waveform, or the antenna directly connects 75Ω inputs in the frequency meter. If there is no above test instrument, it is necessary to use a multimeter to perform a DC voltage measurement, see if the oscillating tube Q2 has the correct value pressure. Measurement base voltage and emitter voltage, a common multimeter is due to its circuit action, which indicates that this is about 2V, only high impedance meters, such as FET voltmeter, indicating that the shot is 2V and base There is 2.5V. (Recommended Number Table) If the two test points have a voltage exist, it is possible to operate the transistor normally, but it is possible to transmit an error frequency. The 18PF return capacitor is fitted to the BC547 transistor, such as using another number, can reduce the capacitance value to 10 pf or 5.6 pF. Convert this capacitor first, then the transistor. Other simple things such as copper foil on the bottom plate, the welding point is infer, or use no number of parts, this is often a possibility, especially the number or numerical value in the parts, if it is unclear, if There is a doubt that it should be replaced. If only the carrier is received but there is no pure tone, the fault is on the audio stage or the microphone. The so-called carrier has no pure tone is in the tuning radio, it is silent, there is no sand, but it can't hear the pure sound signal issued by the transmitter. These two parts can be checked with an oscilloscope, and the test is available to the oscillation level. There is no oscilloscope, which is difficult to test in terms of testing, even if there is a voltage between 0.7V and 1.5V on the microphone, this does not mean the sensitivity or complete work of the microphone. The audio amplifier tube set has a 1.4V voltage, indicating that the transistor is turned on, such as less than 0.8V, transistor saturation, or may be damaged in a certain aspect, may also indicate that the transistor has a high gain and is not suitable. If the voltage exceeds 2.5V, this stage is not sufficient to conduct the inspection of transistors and bias resistances, and replace it when needed. The oscilloscope also shows the sensitivity of the microphone, increases or reduces load resistance, which can change the gain of the FET, a very high sensitivity, and load resistance should not be less than 10K, sometimes as high as 47K or more. Any category of microphones, if you want to improve its sensitivity, increase the value of load resistors, as for determining the ultimate value to see the quality of the microphone. The above is the inspection that can be done with a simple test instrument. If the fault is still not found, it needs to be re-ever. The bottom plate is placed in a matchbox with the battery. If the bottom plate can be placed on one side, the space occupied is the smallest. With a row of match cover, you can stick the criminal on a thin card paper, and the antenna is attached from one end of the matchbox. On the other end, open a small hole, let the sound go to the microphone, but not to make this, because it is in the box, the sound seems to be penetrated. As long as a short antenna is about 10 cm, there can be 30 meters of launch range, enough room for communication, and even more housing can also be cope. "
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