Description
Brief introduction
This is the simplest form of FM transmitter, capable of transmitting broadcast music or voice to a range of up to 50 meters, depending on the type of antenna used. The system works without tuning and the quartz crystal used is locked to a maximum of 90MHz. This system eliminates frequency drift, a common effect of modern LC-based transmitter systems.
Components and Requirements
AE1, 1 Antenna Antenna Connector_Wire:SolderWire-0.1sqmm_1x01_D0.4mm_OD1mm Antenna
C1, 1 piece 10u, 35V CP1_Small Capacitor_SMD:C_0805_2012Metric Polarized capacitor, small US symbol
C2, 1 100u 35V CP1_Small Capacitor_SMD:C_0805_2012Metric Polarized capacitor, small US symbol
C3, 1 330p C_Small Capacitor_SMD:C_0805_2012Metric Unpolarized capacitor, small symbol
C4, C6, 2 100n C_Small Capacitor_SMD:C_0805_2012Metric Unpolarized capacitor, small symbol
C5, 1 33p C_Small Capacitor_SMD:C_0805_2012Metric Unpolarized capacitor, small symbol
D1, 1 1SV149 D_Capacitance Diode_SMD:D_0805_2012Metric Varactor Diode
J1, 1 AudioJack2 AudioJack2 Connector_Coaxial:U.FL_Hirose_U.FL-R-SMT-1_Vertical Audio Jack, 2 pole (Mono / TS)
J2, 1 12V battery. Conn_01x02 Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical Universal connector, single line, 01×02, script generation (kicad-library-utils/schlib/autogen/connector/)
L1, 1 L_Small L_Small Inductor_SMD: L_0805_2012Metric Inductor, small symbol
Q1, 1 PN2222A PN2222A Package_TO_SOT_SMD: SOT-323_SC-70_Handsoldering 1A Ic, 40V Vce, NPN Transistor, Universal Transistor, TO-92
R1, 1 330E R_Small_US Resistor_SMD:R_0805_2012Metric Resistor, small US symbol
R2, 1 100K R_Small_US Resistor_SMD:R_0805_2012Metric Resistor, small US symbol
R3, 1 10K R_Small_US Resistor_SMD:R_0805_2012Metric Resistor, small US symbol
R4, 1 4.7K R_Small_US Resistor_SMD:R_0805_2012Metric Resistor, small US symbol
R5, 1 150E R_Small_US Resistor_SMD:R_0805_2012Metric Resistor, small US symbol
RV1, 1 10K R_POT_US Potentiometer_THT:Potentiometer_Bourns_3266W_Vertical Potentiometer, US symbol
U1, 1 LM386 LM386 Package_TO_SOT_SMD:SC-70-8 low voltage audio power amplifier, DIP-8/SOIC-8/SSOP-8
Y1, 1 30MHz Crystal_Small Crystal: Crystal_SMD_0603-2Pin_6.0x3.5mm two-pin crystal oscillator, small symbol
Circuit system and its working principle
The system is built around a low power audio amplifier LM386, PN2222A transistor, 1SV149 varactor diode, 30MHz quartz crystal and other components such as potentiometers, diodes, capacitors and resistors.
The built-in energy storage circuit at the collector of PN2222A consists of inductor L1 and capacitor C5, and the tuning frequency is 3 times the rated frequency of the quartz crystal, which is 90MHz. The 90MHz is boosted and then coupled via capacitor C4 to a wire antenna used to transmit music or audio so that an FM receiver 30 t0 50 meters away can pick up the transmission.
Printed circuit board layout
The figure below shows the PCB layout of the FM transmitter system.
Due to high precision requirements, the design is completed using KiCAD EDA, where components are arranged according to the circuit in preparation for production.
The three-dimensional rendering of the system is as follows:
Build such a model
Such models can be built at home using a breadboard and all the components listed, but for better quality, PCBway offers manufacturing services for such boards, which for me is the best option available.
KiCAD has a PCBway plugin that helps you with one-click ordering.
Open your KiCAD and click on Plugins and Content Manager as shown by the cursor in the image below.
Scroll down to Kicad’s PCBway plugin and click Install. see Attachment;
The plugin is now fully installed.
The benefit of this plugin is that with just one click you can export all your manufacturing files to PCBway and place your order instantly without having to download the files to your computer and submit them manually on the PCBway Instant Quotation online page.
