FM Transmitter System Board

Brief Introduction

This is the simplest form of FM transmitter which has the capability of transferring broadcasted music or voice to a range of 50m depending on the type of antenna that has been used. The system works without the requirement of tuning and the crystal quarts used are locked to a maximum of 90MHz. This system can eliminate frequency drift which is 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 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 Variable capacitance diode

J1, 1 AudioJack2 AudioJack2 Connector_Coaxial:U.FL_Hirose_U.FL-R-SMT-1_Vertical Audio Jack, 2 Poles (Mono / TS)

J2, 1 12V BAT. Conn_01x02 Connector_PinHeader_2.54mm:PinHeader_1x02_P2.54mm_Vertical Generic connector, single row, 01x02, script generated (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, General Purpose 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, small symbol

Circuit system and how it works

The system is built around low power audio amplifier LM386, PN2222Atransistor, 1SV149 varactor diode, 30MHz crystal quartz, and several other components like potentiometer, diodes, capacitors, and resistors.

The tank circuit built at the collector of PN2222A which is made up of inductor L1 and capacitor C5 has a tuning of 3 times what the crystal quartz is rated which is 90MHz. The 90MHz is boosted and then coupled through capacitor C4 to the wire antenna for the music or audio to be transmitted so that a 30 t0 50m away FM receiver can pick the transmission.

PCB Layout

A PCB layout for the FM transmitter system is shown in the figure below.

Due to the high accuracy requirement, the design is done using KiCAD EDA whereby the components are arranged according to the circuit in preparation for production.

The three-dimensional rendering of the system is shown below

Building 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, and for me, it is the best option available.

KiCAD has PCBway plugins that could help you make a one-click order.

Open your KiCAD and click on Plugin and Content Manager as shown by the cursor in the image below.

Scroll down to PCBway plugin for Kicad and click on install. See the image attached;

The plugin is now fully installed.

The benefit of the plugin is that with just a single click, you will be able to export all manufacturing files to PCBway and make your order instantly without having to download the files to your computer and submit them manually on the PCBway instant quote online page.