Make a wireless microphone circuit using a lighter shell

Small and exquisite lighters come in various shapes. Using discarded lighter casings to make a wireless microphone can not only exercise your hands-on skills, but also add a little fun. The specific method is as follows: Choose a lighter shell of appropriate size. Pay attention to the space inside the lighter gas tank that can accommodate the circuit board with all the electronic components soldered and four button batteries. First carefully remove the metal windshield, plastic button and pressure lighter on the upper end of the lighter, and then remove the flame nozzle and air tube. Then use an electric drill to drill a few small ∮5mm holes in the lower end of the lighter case, then use a wood carving knife to reach into the holes to dig out the middle partition in the gas tank, and remove the waste residue. The power switch is a commercially available long-handled touch button switch. The overall length should be the actual length of the pressure lighter. In addition, a small spring of corresponding length is added to the long handle to increase the restoring force of the power switch and also enhance the The feel. Circuit principles. Figure 1 is the schematic diagram of the wireless microphone circuit. Transistor VT1 is responsible for audio amplification, and VT2 is responsible for high-frequency oscillation. After the electret microphone BM turns the sound of human speech into an audio electrical signal, it is sent to triode VT1 for audio amplification through C2. The amplified audio signal is coupled by C3 and then modulated. The high-frequency oscillation signal causes the be junction capacitance of VT2 to change with the change of the audio signal voltage, so L emits frequency modulated electromagnetic waves to the outside. Using an FM radio to receive signals, you can receive the sound of people talking from the radio. If the middle tap of coil L is connected to a plastic soft rubber wire about 50mm long through C7 as a transmitting antenna, the transmitting effect can be enhanced and the communication distance can be increased. Production and debugging. In order to reduce the size of the whole machine as much as possible, VT1 in the picture can choose 2SC9014 miniature high-frequency triode; VT2 can choose 2SC9018 miniature ultra-high frequency triode; BM should choose N8mm electret miniature microphone; C1, C4, C5, C 6. C7 should Use ultra-small high-frequency ceramic capacitors; 6.3V ultra-small electrolytic capacitors should be used for C2 and C3; all resistors use 1/32W metal film resistors; coil L uses ∮0.51mm enameled wire flat on a ∮5mm round rod It is made of 7 turns and can be tapped at the center to facilitate the installation of the transmitting antenna; the battery GB uses four button batteries; the switch S uses a long-handled light touch button micro switch (if the length is not enough, try to extend the handle and Add a spring of corresponding length): The connecting wires of the microphone and power switch and the transmitting antenna are all made of ∮0.05mm×5 multi-stranded soft rubber wires. The printed circuit board diagram in Figure 2 is suitable for a rectangular lighter casing, and the circular printed circuit board diagram in Figure 3 is suitable for a square lighter casing. Enthusiasts can also make separate printed boards according to their actual conditions. The debugging method of this machine is: 1) Adjust R2 so that the VT1 collector current is 0.6mA, adjust R4 so that the VT2 collector current is 2.5mA; 2) Place the radio at 100MHz in the FM band, and slightly stretch or shorten the coil L length, so that the transmitting and receiving frequencies are very close to each other for the best effect, seal the coil L with hot melt glue. After the debugging is completed, first put the circuit board into the lighter can shell, and pass the leads connecting the switch and microphone through the small hole on the top of the shell, and install the power switch where the piezoelectric lighter was originally installed; Install the microphone where the flamethrower was originally installed, install the original buttons and windshield; and install the battery into the machine from the rear opening of the casing (the battery must be wrapped with transparent tape to prevent short circuit and leakage of electrolyte) , then use plexiglass to make a small cover and dip it in transparent all-purpose glue to seal it. If you want to install an antenna, you must leave a small hole for connecting the antenna. The wireless microphone looks like a lighter from the outside. When using it, just press the original lighter button (actually the power switch inside the machine) with your finger to turn on the power of the microphone, and the microphone starts to work; if you release your hand from the button, the switch will automatically turn off. Turn on the power and the microphone stops working.