Posted on Tuesday, February 18, 2014 • Category: FM Transmitters
Here's FM transmitter for commercial FM band that provides 18 watts of power. Since the electronic diagram is too large we decided to divide it into two parts. The first part is the actual FM transmitter while the second part is 18W RF amplifier. The circuit should be built on an epoxy printed circuit board with the upper face components reserved for interconnecting tracks and the bottom solder to the ground plane. If powered by 14V and 2.5A transmitter outputs 15W of power, whereas 18V and 3.5A will provide 18W. BB110 variable capacitor connected to the collector of transistor BF199 adjusts the transmission frequency of the circuit. 2K2 potentiometer serves as fine tuning. Once the output frequency is adjusted amplifier variable capacitors must be adjusted for maximum output power one stage at a time. All adjustments must be made with 50 Ohm dummy load connected to the output of transmitter.
Posted on Friday, February 14, 2014 • Category: Solar Circuits
As the world around us becomes more and more environmentally conscious, alternative energies such as solar power are becoming more and more popular. The following solar charger is very simple and inexpensive to build and could be used to charge cellphones, tablets and other USB devices. 6V solar panel could be easily salvaged from outdoor garden lights. Solar charger uses REG113-5 efficient low dropout regulator that only loses 250mv of forward voltage. Linear style regulators such as a LM7805 or LM317 type voltage regulators lose as much as 2-3V and can not be used in this application. Optionally you may also add four-resistor voltage divider to charge an iPhone or iPad.
Posted on Tuesday, January 28, 2014 • Category: AC / DC Innveters
Here is a simple but powerful, stable and efficient schematic diagram for a 500W modified sine wave inverter circuit. Originally I used a 555 timer and a CD4017 decade counter to produce the modified sine wave, but then I thought a simple PIC micro controller with its internal clock would produce a stable 50Hz/60Hz frequency without the need for two ICs. As you can see its a very simple circuit. 220V transformer should be used for 220V voltage output. For 110V voltage output use transformer with 110V rating.
Posted on Wednesday, January 22, 2014 • Category: Power Supplies
I normally use a USB port as power supply for my projects but some ICs need 3.3V instead of 5V. Therefore I decided to build this small dual power supply. Power supply uses two low dropout voltage regulators that provide up to 800mA of output current and come in TO-220 package. LD1117V33 is used for 3.3V and LD1117V50 for 5V. Input voltage is 6V-15V and both regulators can be switched on/off individually.
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.
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