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300m FM Transmitter
Posted on Thursday, April 7, 2011   •   Category: FM Transmitters


This FM transmitter is about the simplest and most basic FM transmitter it is possible to build and have a useful transmitting range. It is surprisingly powerful despite its small component count and 3V operating voltage. It will easily transmit over 300 meters in the open air and even more with higher voltage supply. The circuit we use is based on a proven Australian design. It may be tuned anywhere in the FM band. Or it may be tuned outside the commercial M band for greater privacy. Of course this means you must modify your FM radio to be able to receive the transmission or have a broad-band FM receiver. The output power of FM transmitter is within the legal limits of many countries. However, some countries may ban all wireless FM transmitters without a license. It is your responsibility to check the legal requirements for the operation and to obey them. FM transmitter is constructed on a single-sided printed circuit board PCB.


Power RGB LED Controller
Posted on Wednesday, April 6, 2011   •   Category: LED


Power RGB LED Controller is the extension of tiny RGB to drive high power LEDís. For this project I used a 3 x 1W common Anode RGB LED. Q1 to Q3 are N-Channel HEXFet Mosfetís with logic level drive and a RDSon at about 50mOhms. R1 to R3 are at about 2k2, R4 to R6 at about 15k and R7 to R9 depend on the LED used and VCC. If you use FETís with higher RDSon you have to consider RDS in your calculation!


Lithium Ion Battery Charger with Microchip MCP73831
Posted on Wednesday, April 6, 2011   •   Category: Battery Chargers


Here's a simple and inexpensive compact lithium ion / polymer battery charger based on Microchip's MCP73831 IC. It features adjustable current charging from 15mA up to 500mA for single cell lipo batteries. With this lipo charger just a few external components are needed. Constant voltage power supply of 5 ~ 6V is needed. Power can also be drawn from USB port. When USB power is 150mA charge current should not be higher. Charge current can be adjusted with external resistors. External LED provides status when lipo battery is fully charged. The LED lights when battery is fully charged. The maximum charging voltage is selectable from 4.2 to 4.5. This has to be chosen at the time of purchase. Typically 4.2V is a standard charging voltage. MCP73831-2 <- 4.2V, MCP73831-3 <- 4.3V, MCP73831-4 <- 4.4V, MCP73831-5 <- 4.5V.


24V to 12V 400W DC Inverter
Posted on Wednesday, April 6, 2011   •   Category: AC / DC Innveters


24V to 12V 20A 400W DC to DC Inverter. Does little to change my PV system 12v 24v me the problem arose of what to do with investors who already had 12V. I was looking for a pattern online and found several schemes with linear regulators 20A, this solution although quite simple, due to the huge losses they have is not advisable. Ideally, a converter switched, high-performance. At the end I found nothing I liked and decided to design my own. Circuit characteristics: Output current: 20A at 12V (15A continuous and 30A Momentary), Input voltage: 18 to 30V DC, Output voltage: 5 to 20V, Operating Frequency: 70kHz, Effectiveness: 95%, 400W maximum power, Protections: Above current (30A) in the F1 circuit, D1 and F1 polarity in the circuit.


PLL FM Transmitter using LMX1601, ATtiny2313 AT90S2313
Posted on Tuesday, April 5, 2011   •   Category: FM Transmitters


Here's a PLL FM Transmitter using LMX1601, ATtiny2313 or AT90S2313 microcontrollers. The common characteristic of all of the previous low power FM transmitters I've built over the decades, is that their operating frequency is determined by an LC resonant circuit. Some of them had excellent stability, some of them didn't, but I had always wanted to make one that is crystal controlled. Various schemes had been considered from time-to-time, including the direct approach of modulating the load capacitance of a a crystal oscillator, a whimsical phase modulation scheme involving a phase shifter, some balanced modulators, and limiting amplifiers, and at times, the down-to-earth and sober approach of modulating a VCO within a phase locked loop (PLL). While browsing Digikey's online catalog, I found the LMX1601 frequency synthesizer chip and thought: "Just maybe, the PLL approach is finally within my grasp." The LMX1601, which apparently was designed for use in cell phones, includes everything need to make two phase locked loops except for the VCOs. More importantly, one of the PLLs, specifically the "AUX" PLL, is specified to work in the FM broadcast band. The LMX1600 and the LMX1602 were also considered, but the LMX1601 was selected because it has a "500 MHz option", meaning that it can work down to about 50 MHz.


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