Circuit-Zone.com - Electronic Projects
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.
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.
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.
Posted on Tuesday, April 5, 2011 • Category: USB Interface Adapters
Here's the new 6 channel USB relay card for switching different appliances, lamps or motors by a computer program via the USB interface. There are certain switching sequences can be programmed via computer. The card was dispensed on SMD technology and is thus the ideal craft project for beginners and novices. Those who do not always wanted with his computer what Steruern. This can be done with the help of a web application even over the Internet. About the SPI connector could even imagine the relay card to cascade with other relay boards.
The relays max. 250V AC and have a switching current of 8A (depending on the used relay). Furthermore also 4 inputs, which are separated optocouplers, and monitors can be queried. AVR simulates a USB RS 232 interface can thus this relay, the card without problems using a terminal program or other software to be easily addressed. The USB driver in the AVR firmware was developed by Objective Development ( http://www.obdev.at/products/avrusb/projects-de.html ) and under the GPL2. Through this USB driver could have very special devices and SMD technology abandon. Her come out is a very compact board with dimensions of 100mm x 85mm. The setting of the simulated serial port is: 9600 baud, 8Datenbits, no parity and 1 stop bit further handshaking. To power supply reaches a normal 9 - 12V power supply.
Posted on Monday, April 4, 2011 • Category: Miscellaneous
MOSFET transistors are excellent choice for driving high current devices such as motors or high power RGB LEDs. They offer very low switching resistance and very small heat dissipation compared to bipolar transistors. This guide is designed to explain how to drive N-Channel MOSFETs with a microcontroller such as PIC or ATMEGA. Transistors heat up when driving large loads because they have a voltage dropped over them (Vce), and Heat (Watts) = Voltage * Current. This leads to thermal runaway within the transistor, eventually driving the device to destruction if not handled carefully.
FET's are like digital switches, capable of turning on and off between the Drain and Source via a voltage potential at the Gate. When a FET is on, it usually has a resistance of less than 0.01 ohm, and when off, its like an open circuit. Because of the low resistance during the FET's on state, it can allow large amounts of current to pass through it without heating up.
FET's turn on by voltage potential, not an electric current, and in return they have a very high input impedance. With this in mind, you only need a voltage to turn them on, perfect for digital electronics.
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