This section describes a simple wireless microphone. Can be implemented in the FM radio band wireless transmitter. This machine can be used to monitor, signal forwarding and electronic teaching. As the structure is simple, easy to install tune, so it is suitable for beginners devices.
A wireless microphone circuit and working principle
Figure 3-34 is the FM wireless microphone circuit.
Figure 3-34 of the wireless microphone circuit
Electret microphone audio into the sound current, the increase in the transistor V, coil L and capacitor C1 form a high-frequency oscillator, the formation of the FM signal from the antenna into space. Within the range of 10 meters, by a FM radio band (FM band) radio receiver, the speakers restore the original sound, the sound implementation of wireless transmission.
Second, the component specifications and test methods
The simple structure, including battery, a total of eight components.
Ceramic capacitor C1 to C2 for the 10PF 10uF electrolytic capacitor to lk 1/8W carbon film resistors R k is the toggle switch for the high-frequency transistor 9018 V for small electret microphone on BM L is hollow coil.
The higher sensitivity electret microphone, wireless microphone, the better. Its shape and test methods shown in Figure 3-35, when blowing on the microphone, the greater the multimeter pointer swing, the more sensitive electret microphone.
Figure 3-35 electret microphone detection
L is the inductance of the coil hollow. Use? 0.5 mm enameled wire beads per cartridge in around 10 laps on the secret. With a knife to scrape off the paint at both ends of the coil after the tin can point some of the paraffin oil per bead fixed coil and then out of the cartridge to form a hollow coil (Figure 3-36).
Third, the welding circuit
Figure 3-37 is a printed circuit FM wireless microphone.
图3一36 线圈L的绕法
Figure 3 a printed circuit board 37
1 will be inserted after the element tin pin printed circuit board corresponding to the position. Each component pin should be left short.
(2) welding the components one by one pin. Joints should be small and should not be smooth and fake welding Weld. Welding coil, be careful not to make the coil deformation.
3 40-60 cm long with a plastic multi-strand leather cord do Antennas. One end of the solder on printed circuit boards, the other side of the natural stretch.
Fourth, the circuit debugging
1 to check the printed circuit board and soldering, should short-circuit element and the imaginary, false welding phenomenon. You can then power.
2 measured with a multimeter DC voltage profile V transistor base-emitter voltage of Q, should be about 0.7 volts. If both ends of the coil L short, there should be a change in voltage, indicating that the circuit has been oscillation.
3 Turn on the radio, pull the radio antenna, band switch in the FM band (frequency range 88 MHz to 108 MHz) will take the wireless microphone on the radio antenna.
4 Turn the radio tuning knob slowly, while blowing on the microphone or speech. Transferred to the received radio signal heard. If the radio does not receive the signal within the tuning range can be stretched or compressed coil L, change its width, and then carefully tune the radio until the radio receives a clear signal. And then gradually pull the wireless microphone and the distance between the radio until the distance of 8 ~ 10m, can still receive a clear signal. Note that debugging should avoid wireless microphone transmitter frequency within the FM band radio frequencies.
5 printing plates into the wireless microphone case. Case can be made, it can be cylindrical plastic bottles. Switch should be exposed in the outer shell, easy to use (see Figure 3-38).
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