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Micro Transmitter with Buzzer (ART499E)

Piezoelectric transducers used in buzzer or even tweeters can function as excellent high impedance microphones. In this article we show how to mount a small FM transmitter using one of these buzzers as a microphone. The circuit has a range of 50 to 200 meters.

Buzzers found in various types of devices consist of a ceramic transducer that can operate both reproducing sounds, and conversely, as a microphone. The sound vibrations it picks up deform the material that then produces a voltage that can be used by an electronic circuit.

In our case, the buzzer acts like a microphone, modulating a small transmitter of only one transistor that operates in the FM range.

 

Assembly

In figure 1 we have the complete diagram of the transmitter.

 

Figure 1 - Transmitter complete diagram
Figure 1 - Transmitter complete diagram

 

In figure 2 we have a suggestion of assembly using a terminal strip.

 

Figure 2- Assembly using terminal strip
Figure 2- Assembly using terminal strip

 

The coil is formed by 4 coils of ordinary strand 22 rigid or enameled enamel 24 to 28, with a diameter of 1 cm without core. The trimmer can be either the old porcelain-based type harnessed from old out-of-use appliances like modern plastic rounds, with maximum values of 10 to 30 pF.

The Capacitors must be ceramic and the antenna can be either a 10 to 30 cm piece of hard wire or a telescopic antenna. The set can be installed in a small plastic box, where there are also two batteries that will power it.

 

Test and Use

Simply turn on the unit and adjust the trimmer to pick up your signal on an FM receiver tuned to a free frequency, placed nearby. Look for the strongest signal and step back to check its range.

When operating, always keep the antenna in an upright position away from your hand or any object.

 

Q1 - BF494 - RF transistor

BZ - Ceramic transducer (buzzer)

R1 - 8k2 x 1/8 W- resistor - red, gray, red

R2 - 6k8 x 1/8 W - resistor - blue, gray, red

R3 - 47 ohm x 1/8 W - resistor - yellow, violet, black

C1 - 4n7 - ceramic capacitor

CV- trimmer - see text

C2 - 47 pF - ceramic capacitor

C3 - 100 nF - ceramic capacitor

S1 – On/Off switch

B1 - 2 AA or AAA batteries

 

Several:

Terminal block, 2-cell holder, mounting box, wires, solder, etc.