I have ever shown you an FM Wireless Microphone circuit. It is good to play with our kids. Or Learn RF transmitter circuit works.
But, is the distance too short?
Try this circuit. Add another one transistor in an RF amplifier.
So, this has two resonance circuits, and also two trimmers. Cause Higher efficiency and more transmission far up.
- Use DC Power supply of 9V
- Maximum consumption current about 10mA
- Transmission frequencies in the 88 MHz.
- PCB dimensions: 1.64 x 1.54 inches.
How does FM wireless microphone works
Figure 1 Two transistors FM wireless microphone circuit
Look at Figure 1:
A MIC1-condenser microphone is an audio receiver. It converts our voice to an audio signal.
Then, the signal flows C2 is a coupling capacitor into the base of Q1-transistor.
Which this transistor and a few parts around itself, have 2 functions.
First, generate high-frequency oscillators.
Second, mix audio signal into radio frequency (RF).
Then, the RF signal comes to the base of Q2 through the coupling capacitor-C5. The Q2 amplifies the RF goes out of a collector.
Then, send out to an antenna.
At collector lead of Q1 and Q2 have copper wires. They are working as a general coil.
How to builds its.
As Figure 2, the components layout and wiring of this project.
I am so sorry for cannot show PCB layout for you.
Then Figure 3, the complete FM wireless microphone circuit on PCB.
Testing the FM wireless microphone
First, apply the 9 volts battery to the positive terminal (+9V) and negative (G terminal).
Second, for ANT point connects to the coil.
You have to scrape off the enamel of copper coil. before soldering it.
Then, Set the FM radio stations to positions 88 MHz.
Next, use a plastic screwdriver to gently adjust the trimmer VC1, Until it whistles howling out the radio.
After that, try to speak into the microphone.
However, if no sound on speakers. You may try to turn the radio to about 100MHz.
If this is still no sound, you turn the radio all the way to 108MHz and try again.
Then, adjust Trimmer-VC2 in order to get more distance.
Also FM wireless transmitter
The components list
R1, R2: 27K
R4: 270 ohms
R6: 470 ohms
C1: 0.022uF (223)
C3, C6: 0.01uF(103)
C4, C5: 3pF
Q1, Q2: 2SC458, 2SC828, 2SC945, 2SC1815
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