Posted on Sunday, December 29, 2013 • Category: FM Transmitters
Veronica 1W FM transmitter is an easy to build transmitter. Veronica is also known for frequency stability, clean FM signal and uses no integrated circuit. The Veronica oscillator is actually formed from 2 oscillators which operates somewhere around 50 MHz in anti phase and the 2 signals are combined to form 100MHz FM radio signal. This kind of circuit design is stable and is amplified up to 1W by 2n4427 transistor. Veronica transmitter is equipped with a mini-mixer and so you may forget an external mixer. This consist from T1 transistor which amplifies the microphone signal before it is combined with cd-player audio or PC signal. R1 and R2 are potentiometers (variable resistors) used to adjust the audio level. The component between R8 and C21 represents the oscillator wich generates radio signal. D1 is a varicap diode (like a variable capacitor or trimmer) controlled by audio signal. C12, C13 and L1 determines the frequency.
Posted on Sunday, December 29, 2013 • Category: LED
The "Joule Thief" circuit that does not use a transformer to power LED from a single 1.5V battery cell. The circuit consists of two bipolar transistors, coil, two resistors and capacitor to generate higher voltage through 50KHz frequency to power an ordinary LED. Entire circuit draws only about 15 milliamps.
Posted on Wednesday, December 18, 2013 • Category: FM Transmitters
Following 1W PLL transmitter exciter provides stable, low noise operation. Transmitter uses a PLL frequency synthesizer built with MC145152 which covers the FM band in 100kHz steps. The VCO uses MV2109 varicap diode to automatically tune to selected frequency via SW1 dip switch. output stage uses 2N4417 RF power transistor and provides 1W of RF power. With good antenna expected transmission range is 2km. Transmitter may be built on a double sided PCB, with top side copper left mostly undisturbed as a ground plane. The copper is removed only around non-grounded pins. The ground connections can be soldered on the top side, so it’s not necessary to have plated-through holes.
Posted on Friday, December 13, 2013 • Category: LED
I like the idea of using LED Christmas lights because they look cool and consume very small amount of electricity, but the flicker drives me crazy! That's because they are powered directly from 110V AC voltage instead DC voltage which makes them flicker 60 times per second. Here is a simple circuit that will completely eliminate LED Christmas lights flicker. The solution is to convert AC to DC voltage with resistor, rectifier diode and capacitor. Using 470 ohm - 1K resistor is very essential because it limits the current to 20mA and minimizes the voltage to about 80 volts. If we didn't use the resistor LEDs would be powered by over 50mA of current which is much more than what they need and that would definitely shorten their life. Note that lowering voltage does not reduce the brightness of the LEDs because when powered by DC voltage they are always on.
Posted on Thursday, December 12, 2013 • Category: FM Transmitters
Here is a very interesting and simple FM transmitter used to transmit audio in the wide range up to 100M using only one transistor. The entire circuit of FM transmitter is divided into three major stages oscillator, modulator and amplifier. The transmitting frequency of 88-108 MHz is generated by adjusting VC1. The input audio generated by microphone is changed into electric signal and is given to base of transistor T1. Transistor T1 is used as oscillator which oscillates the frequency of 88-108 MHz. The oscillated frequency depends upon the value R2, C2, L2 and L3. Transmitted audio from FM transmitter circuit can be received by standard FM receiver.
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