Homemade wireless microphone circuit

1, Production notes

The FM microphone has a frequency stability, making simple, one mounted on a characteristic . Is ideal for beginners interesting strong electronic production. The high sensitivity of the microphone, the microphone can pick from three meters outside the minor speech sound; effective transmission range of 100 meters.


2, the circuit


3, simple circuit analysis

C8 is the power supply bypass capacitors. R1 is biased to provide a microphone MIC quiescent operating point. R1 now constitute the MIC pickup loop. C1, C2 coupling from the sound signal. R2, D1, D2 composition limiter circuit prevents the microphone at close range when the input signal is too large and serious distortion. R3, R4 is used to provide quiescent operating point Q1. C3, C4, C5, C6, L1, Q1 constituting the oscillation amplification. C7 is coupled to the antenna signal. Antenna will have been modulated sound signal emitted by the circuit from a 3V supply, with two 1.5V batteries can.

4, test

A, if you bought the discrete component, you can assemble it and measure it at the same time. And also you can assemble them first then measure.

B, the battery pack connected to the PCB board, and then replace the battery in the VCC and ground terminal measurable voltage of about 3V.

C, mounted on R1, MIC. If you have an oscilloscope, you make with the whistle at point A can be measured to about 2mV sinusoidal waveform, the waveform as your whistles and downs.

D, put on R3, Q1, R4, then, with a millimeter at C can be measured voltages around 1V, which determines the quiescent operating point Q1.

E fitted C1, R2, C2, C3, C4, C5, C6, L1, C7 antenna. C7 straight wire can be used instead. Welding is completed with an oscilloscope can be observed at the high-frequency oscillation in D, if your oscilloscope can measure the frequency is not high does not matter, see a columnar waveform. This proves that the circuit has started work at this point.

F, turn on the radio in the FM band search , when tuned to somewhere still feeling a sudden noise , or howling occurs , it indicates that the frequency of this FM transmitter microphone in here . At this point you hand by pressing L1, you can feel the hair on the radio frequency up or down somewhat. That is by changing L1 (five turns of the coil) can change the transmission frequency. Note coil gap is too big, or too small may lead not receive radio voice.

G, in order to increase the distance you will be receiving antenna extension, straightening.

H, when these have been satisfied with the last connected D1, D2. This makes the handset has a wider operating range.


The list of components electronic parts


No.    Name      Model / Spec           QTY

An FM microphone PCB board DZZZTPWXHTSJ * 1

2 battery box can be mounted two AA batteries * 1

3 ordinary microphone * 1

4 Resistor 15K ohms * 1

5 Resistor 12K ohms * 1

6 Resistance 300 Ohms * 1

7 100 ohm resistor * 1

8 ceramic capacitors 100Pf * 1

9 ceramic capacitors 1000pf * 1

10 ceramic capacitors 10000pf * 1

11 ceramic capacitors 6.8Pf * 1

12 ceramic capacitor 22pf * 1

13 electrolytic capacitor 4.7uf * 2

14 electrolytic capacitor 220uf * 1

15 LED 4148 * 2

16 transistors 9018 * 1

17 thin straight wire 20 cm * 1

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