Micro FM FM wireless microphone can be installed in a matchbox

Circuit Overview: Here, a pocket transmitter introduced here is very suitable for beginners, simple circuits, low cost, no output power, no more than 5-8MW, the launch range can be around 300 meters, with a normal FM radio Receive, showing its sensitivity and clarity, the richest part of the circuit design is to have such launching capabilities only with 3V power and half-wave antennas. In addition, since the parts required for the circuit are less, it can be placed in a matchbox (larger-like matchbox), as a wireless microphone, can be said that God does not know, the ghost is not limited to this area On, it 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 easy to achieve good range working principle: From the figure (1) circuit, it is visible to two levels, first-stage audio amplifiers, and one-stage 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 amplification is carried out by its emitter crystal thrust Q1, and the gain is from 20 to 50, and the zoomed signal is sent to the base of the oscillation level. The oscillation level Q2 is operating at a frequency of about 88 MHz, which is adjusted by the oscillation coil (a total of 5 laps) and 47PF capacitor, which is also determined in the transistor, 18pf back-activator, and a few biasing elements, such as 470 Ω emitter resistance. And 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 extreme operating voltage, there will happen several messy week waves, so we assume that the base voltage continues to rise at the time of the working voltage, and the 18NF capacitor attempts to prevent the movement of the shot by pressure. When the energy exhausted in the capacitor and no longer prevents the shot moving, the substance voltage is lowered, the transistor is turned off, and the current of the flow of the flow of the flow of the flow of the flow is also stopped, and the magnetic field is declaced. 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. Be Production process: Before the decoration, it is best to prepare the printed plate and two batteries, 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 wireless microphone. 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 0.5mm) or 24 BS (фm.71mm) paint brass or bag copper wire, from the 3mm diameter coil rack around 5 laps. For the mid-type screwdriver, it can also be separated from 5.5 mm to the circle and the circle. 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, in a 10 cm long copper wire, on the "A" point of the bottom plate, as antenna, the entire manufacturing process is completed. Be Be Be Be Be Be Be Be Be Be Circuit debug: After all parts are soldered, it is best to check all the welding points with naked eye. Is there a fake soldering, or the solder is used to use too much, and after a thorough understanding, calibration and test performance can be performed, the test step is Add a short antenna (5 to 10 cm long) tuning the A point of the bottom plate - the part FM radio is on the entire band, looking 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 the carrier is detected, the wireless microphone * is placed on a clock, check the sensitivity of the circuit, the radio should make a clear "tip" sound, 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 that the frequency of the launch is completely left to leave your local FM broadcast Tuna, because the signal is strong, when you test the distance, the wireless microphone is covered. 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? The carrier from the wireless microphone cannot be received on the FM receiver, first assume that the frequency is lower than the normal 88-108MHzFM band, which is the most likely reason. 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 (3), 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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