Here’s a variable voltage  power supply circuit using a LM338 adjustable 3 terminal regulator to supply a current of up to 5A over a variable output voltage of 2V to 25V DC. It will come in handy to power up many electronic circuits when you are assembling or building any electronic devices. The schematic and parts list are designed for a power supply input of 240VAC. Change the ratings of the components if 110V AC power supply input is required.

The mains input is applied to the circuit through fuse F1. The fuse will blow if a current greater than 8A is applied to the system. Varistor V1 is used to clamp down any surge of voltage from the mains to protect the components from breakdown. Transformer T1 is used to step down the incoming voltage to 24V AC where it is rectified by the four diodes D1, D2, D3 and D4. Electrolytic capacitor E1 is used to smoothen the ripple of the rectified DC voltage.

Diodes D5 and D6 are used as a protection devices to prevent capacitors E2 and E3 from discharging through low current points into the regulator. Capacitor C1 is used to bypass high frequency component from the circuit. Ensure that a large heat sink is mounted to LM338 to transfer the heat generated to the atmosphere.

Source: 2- 25V 5A Power Supply LM338

Audio Analyzer

Mini Audio Spectrum Analyzer LM3915

The circuit has been designed to create a spectrum analyzer that will provide an analysis of a sound to determine at various frequencies, the volume of sounds that make up the overall sound spectrum.

Circuit Explanation
The device is sensitive enough to determine the sound wave components of frequency and amplitude with the changing of frequency and the width of an acoustic signal. The proportionality of signal width is indicated by the brightness of LED as it turns ON while the color indicates the proportionality of frequency. In order for the red LED to turn ON in strong signal, the sensitivity of the input circuit is adjusted by resistor R2. The middle signal is represented by a yellow LED while the low signal is indicated the green LED.

The 10 LEDs in 3 lines comprise the display unit which is ensured the IC2 as it functions as a counter decoder represented by the two gates ICa-b.the frequency of the counter is being regulated by R6. No LED will turn ON in the absence of any signal in the input. The LEDs will begin to flicker or blink depending on the intensity and tempo of the signal, once a signal has been applied in the input. The values of the resistors R4 & R5 can be varied that will be suitable for the desired requirements. Alternatively, this can be done by placing a 1K ohm trimmer in place of R4 & R5 during the initial regulation and adjustment of the values. It can be eventually removed and replaced with permanent resistors as soon as the desired values are achieved. Additional LEDs can be added in connection to IC2 although this circuit does not precisely measure the input signal.

Part List
R1= 1K8Kohm
R2= 100Kohm trimmer
R3= 1Kohm
R4= 100 ohm…..1Kohm
R5= 100 ohm…..1Kohm
R6= 100Kohm trimmer
C1= 100nF 100V
D1….10= RED LED
D11….20= YELLOW LED
D21….30= GREEN LED
IC1= LM3915
IC2= 4017
IC3= 4011

Application
This audio spectrum analyzer is a user interface component capable of making visible the sound pressure for a range of frequencies over time by taking a sample from an audio data stream and an animated visualization during the play is created in real time. It is ideal for any purpose which includes analysis and identification of human speech, ham radio audio reception tuning, analysis of vocal and instrumental music, evaluation and tuning of musical instruments, analysis of bat echolocation sounds, evaluation and calibration of home audio systems, and analysis and identification of biological sounds. Other uses of the audio spectrum analyzer are in distortion analysis, transfer functions, and digital filtering.

Source: Mini Spectrum Analyzer for Audio/Sound by LM3915

Car Charger

Auto  Battery Charger 12V

This auto battery charger uses no transformer, rectifier, or filter capacitors on the schematic. No reason why you cannot add these. This charger will quickly and easily charge most any lead acid battery. The charger delivers full current until the current drawn by the battery falls to 150 mA. At this time, a lower voltage is applied to finish off and keep from over charging. When the battery is fully charged, the circuit switches off and lights a LED, telling you that the cycle has finished.

Auto Battery Charger Schematic

A heatsink will be needed for this auto battery charger ( U1.)

Auto Battery Charger Parts List
Resistor
R1  500 Ohm 1/4 W
R2 3K 1/4 W
R3 1K 1/4 W
R4 15 Ohm 1/4 W
R5 230 Ohm 1/4 W
R6 15K 1/4 W
R7 0.2 Ohm 10 W
Capacitor
C1 0.1uF 25V Ceramic
C2 1uF 25V Electrolytic
C3 1000pF 25V Ceramic
Diode
D1 1N457
Transistor
Q1 2N2905 PNP
Regulator
U1 LM350
Op Amp
U2 LM301A
S1 Normally Open Push Button Switch
MISC Wire, Board, Heatsink For U1, Case, Binding Posts or Alligator Clips For Output

To use the circuit, hook it up to a power supply/plug it in. Then, connect the battery to be charged to the output terminals. All you have to do now is push S1 (the “Start” switch), and wait for the circuit to finish.

C1 6800uF 25V Electrolytic Capacitor
T1 3A 15V Transformer
BR1 5A 50V Bridge Rectifier 10A 50V Bridge Rectifier
S1 5A SPST Switch
F1 4A 250V Fuse

If you want to use the auto battery charger without having to provide an external power supply, use above circuit. The first time you use the circuit, you should check up on it every once and a while to make sure that it is working properly and the battery is not being over charged.

12 V Car Battery Charger on Amazon

Source: Car Battery Charger

FM Transmitter

USB Powered Wireless FM Transmitter Circuit

Here’s a Wireless FM transmitter circuit powered from USB ports that could be used to play audio files on a standard VHF FM radio. The transmitter circuit use no coils that have to be wound. This FM transmitter can be used to listen to your own music throughout your home. When this FM transmitter used in the car, there is no need for a separate input to the car stereo to play back the music files from your MP3 player.

This FM transmitter use a chip made by Maxim Integrated Products, the MAX2606 [1]. This IC from the MAX2605-MAX2609 series has been specifically designed for low-noise RF applications with a fixed frequency. The VCO (Voltage Controlled Oscillator) in this IC uses a Colpitts oscillator circuit. The variable-capacitance (varicap) diode and feedback capacitors for the tuning have also been integrated on this chip, so that you only need an external inductor to fix the central oscillator frequency.

Transmitter Schematic

It is possible to fine-tune the frequency by varying the voltage to the varicap. Not much is demanded of the inductor, a type with a relatively low Q factor (35 to 40) is sufficient according to Maxim. The supply voltage to the IC should be between 2.7 and 5.5 V, the current consumption is between 2 and 4 mA. With values like these it seemed a good idea to supply the circuit with power from a USB port.

A common-mode choke is connected in series with the USB connections in order to avoid interference between the circuit and the PC supply. There is not much else to the circuit. The stereo signal connected to K1 is combined via R1 and R2 and is then passed via volume control P1 to the Tune input of IC1, where it causes the carrier wave to be frequency modulated. Filter R6/C7 is used to restrict the bandwidth of the audio signal. The setting of the frequency (across the whole VHF FM broadcast band) is done with P2, which is connected to the 5 V supply voltage.

The transmitter PCB designed uses resistors and capacitors with 0805 SMD packaging. The size of the board is only 41.2 x 17.9 mm, which is practically dongle-sized. For the aerial an almost straight copper track has been placed at the edge of the board. In practice we achieved a range of about 6 metres (18 feet) with this. There is also room for a 5-way SIL header on the board. Here we find the inputs to the 3.5 mm jack plug, the input to P1 and the supply voltage. The latter permits the circuit to be powered independently from the mains supply, via for example three AA batteries or a Lithium button cell. Inductor L1 in the prototype is a type made by Murata that has a fairly high Q factor: minimum 60 at 100 MHz.

Transmitter PCB

P1 has the opposite effect to what you would expect (clockwise reduces the volume), because this made the board layout much easier. The deviation and audio bandwidth varies with the setting of P1. The maximum sensitivity of the audio input is fairly large. With P1 set to its maximum level, a stereo input of 10 mVrms is sufficient for the sound on the radio to remain clear. This also depends on the setting of the VCO. With a higher tuning voltage the input signal may be almost twice as large (see VCO tuning curve in the data sheet). Above that level some audible distortion becomes apparent. If the attenuation can’t be easily set by P1, you can increase the values of R1 and R2 without any problems.

Measurements with an RF analyzer showed that the third harmonic had a strong presence in the transmitted spectrum (about 10 dB below the fundamental frequency). This should really have been much lower. With a low-impedance source connected to both inputs the bandwidth varies from 13.1 kHz (P1 at maximum) to 57 kHz (with the wiper of P1 set to 1/10).

In this circuit the pre-emphasis of the input is missing. Radios in Europe have a built-in de-emphasis network of 50 ?s (75 ?s in the US). The sound from the radio will therefore sound noticeably muffled. To correct this, and also to stop a stereo receiver from mistakenly reacting to a 19 kHz component in the audio signal, an enhancement circuit is published elsewhere in this issue (Pre-emphasis for FM Transmitter, also with a PCB). Author: Mathieu Coustans, Elektor Magazine, 2009

MP3 FM Transmitter Parts List
Resistors (all SMD 0805)
R1,R2 = 22k?
R3 = 4k?7
R4,R5 = 1k?
R6 = 270?
P1 = 10k? preset, SMD (TS53YJ103MR10 Vishay Sfernice, Farnell # 1557933)
P2 = 100k? preset, SMD(TS53YJ104MR10 Vishay Sfernice, Farnell # 1557934)
Capacitors (all SMD 0805)
C1,C2,C5 = 4?F7 10V
C3,C8 = 100nF
C4,C7 = 2nF2
C6 = 470nF
Inductors
L1 = 390nF, SMD 1206 (LQH31HNR39K03L Murata, Farnell # 1515418)
L2 = 2200? @ 100MHz, SMD, common-mode choke, 1206 type(DLW31SN222SQ2L Murata, Farnell #1515599)
Semiconductors
IC1 = MAX2606EUT+, SMD SOT23-6 (Maxim Integrated Products)
Miscellaneous
K1 = 3.5mm stereo audio jack SMD (SJ1-3513-SMT
CUI Inc, DIGI-Key # CP1-3513SJCT-ND)
K2 = 5-pin header (only required in combination with 090305-I pre-emphasis circuit)
K3 = USB connector type A, SMD (2410 07 Lumberg, Farnell # 1308875)

Browse Wireless FM Transmitter on Amazon

See more:  FM Transmitter Antenna

Source: FM Transmitter for MP3 Player Powered from USB

FM Receiver

One Transistor FM Radio Receiver Circuit

Here’s simple FM receiver circuit for a simple superregenerative FM radio. It is sensitive, selective, and has enough audio drive for an earphone. These designs generally have low component counts, however the design or my construction have been far from simple.

FM Receiver Schematic

FM Radio Receiver Circuit Layout
Because this is a superregenerative design, component layout can be very important. The tuning capacitor, C3, has three leads. Only the outer two leads are used; the middle lead of C3 is not connected. Arrange L1 fairly close to C3, but keep it away from where your hand will be. If your hand is too close to L1 while you tune the radio, it will make tuning very difficult.

Winding L1
L1 sets the frequency of the radio, acts as the antenna, and is the primary adjustment for super-regeneration. Although it has many important jobs, it is easy to construct. Get any cylindrical object that is just under 1/2 inch (13 mm) in diameter. I used a thick pencil from my son’s grade school class, but a magic marker or large drill bit work just fine. #20 bare solid wire works the best, but any wire that holds its shape will do. Wind 6 turns tightly, side-by-side, on the cylinder, then slip the wire off. Spread the windings apart from each other so the whole coil is just under an inch (2.5 cm) long. Find the midpoint and solder a small wire for C2 there. Mount the ends of the wire on your circuit board keeping some clearance between the coil and the circuit board.

A tuning knob for C3

C3 does not come with a knob and I have not found a source. A knob is important to keep your hand away from the capacitor and coil when you tune in stations. The solution is to use a #4 nylon screw. Twist the nylon screw into the threads of the C3 tuning handle. The #4 screw is the wrong thread pitch and will jam (bind) in the threads. This is what you want to happen. Tighten the screw just enough so it stays put as you tune the capacitor. The resulting arrangement works quite well.

FM Radio Receiver Circuit Adjustment
If the radio is wired correctly, there are three possible things you can hear when you turn it on: 1) a radio station, 2) a rushing noise, 3) a squeal, and 4) nothing. If you got a radio station, you are in good shape. Use another FM radio to see where you are on the FM band. You can change the tuning range of C3 by squeezing L1 or change C1. If you hear a rushing noise, you will probably be able to tune in a station.

Try the tuning control and see what you get. If you hear a squeal or hear nothing, then the circuit is oscillating too little or too much. Try spreading or compressing L1. Double check your connections. If you don’t make any progress, then you need to change R4. Replace R4 with a 20K or larger potentiometer (up to 50K). A trimmer potentiometer is best. Adjust R4 until you can reliably tune in stations. Once the circuit is working, you can remove the potentiometer, measure its value, and replace it with a fixed resistor. Some people might want to build the set from the start with a trimmer potentiometer in place (e.g., Mouser 569-72PM-25K).

Browse : FM Receiver on Amazon

See more: MP3 FM Transistor

Source: Build A One Transistor FM Radio

Radio-Locator Sticker

How to Search World Radio Station FM Online-Radio Locator

This website is a search engine for finding radio stations FM or AM in the United States and all around the world. Radio-Locator uses a unique search engine to find all the radio stations that can be heard at a specific geographic location in the United States.

This locator search engine takes into account each radio station’s transmitter power, antenna height, frequency, and antenna pattern, as well as the topography and geology of the surrounding area. To find stations in your area, type your city name or zip code (U.S. only) in the appropriate box at the top of this page.

Radio-Locator, the most comprehensive radio station for FM-AM search engine on the internet. Radio-Locator have links to over 10,000 radio station web pages and over 2500 audio streams from radio stations in the U.S. and around the world.

Find Unused Radio Station  FM Frequencies in Your Area

Do you have a satellite radio or MP3 player that transmits sound to your car radio or home stereo?
There are many great audio gadgets available today that include a small FM transmitter and work by sending a signal to any nearby radio that’s tuned to its frequency.

These devices work best if you choose an unused frequency on the FM dial. It’s also best not to pick a frequency that’s too close to a strong Radio FM station. You can use this page to find vacant frequencies in your area that are best suited for use with your audio device.

Radio-Locator

Find unused frequencies on the FM dial

Radio-Locator Online Store

See more: Radio Mobile Software

Main Windows

Radio Mobile RF Propagation Stimulation

Radio Mobile is a free and powerful tool for plotting RF patterns and predicting the performance of radio systems. Using freely available terrain elevation data it can produce grey scale, x-ray and rainbow colored virtual maps. One can also produce 3-D and stereoscopic views as well as flyby animations. Background images can be merged with scanned maps, satellite photos and Mapquest maps to produce accurate prediction plots. You can obtain your copy of Radio Mobile from the official website.

Installing Radio Mobile
There are two ways to install Radio Mobile. You can either download the installer file available through this website or download the individual compressed files from the Radio Mobile website or the QSL.net mirror.

Obtaining Elevation Data
Before you can really do anything with Radio Mobile you need to obtain the proper elevation data for the area in which you are creating plots. Radio Mobile accepts elevations in a number of formats including SRTM, DTED and GTOPO30. Fortunately most of this data is available free of charge and with a little effort is easily installed.

Installing Elevation Data
You have downloaded some elevation data you first need to extract it and then configure Radio Mobile so that it can find it. If you downloaded GTOPO30 or DTED data from the sites mentioned previously you may notice the files have the extension tar.gz. In the UNIX world this is known as a “tarball” and this short 7-Zip Tutorial will show you how to extract the data contained within the tarball you downloaded.

Creating A Map
You have Radio Mobile configured to use your elevation data you can begin creating maps. Click on File | Map Properties and you will again be presented with the Map Properties window. This time make sure you uncheck “ignore missing files” and have SRTM set as one of your data sources. The reason for doing this is to get Radio Mobile to tell you which SRTM data files are missing so you download the missing pieces. There are some holes in the SRTM coverage so there is a chance you will not be able to download the missing files. If this is the case check “ignore missing files” after you have filled in as many missing pieces as possible.

Browse: Radio Mobile Software on Amazon
See more: FM Transmitter MP3
Source: Using Radio Mobile for Windows