The circuit is a LED flasher to light LED with single 1.5V battery is usually based on a blocking oscillator or a charge-pumped voltage doubler.This is another (but similar to charge pump) way to flash LED with 1.5V battery. The base-R voltage becomes nearly double the Vcc while making oscillation timing of astable multivibrator. LED can be flashed if it is attached aside. Since the LED discharges the C electricity, oscillator timing is shortened.
Posted on Wednesday, May 25, 2011 • Category: Power Supplies
This is high current 12V power supply. Power supply uses LM7812 IC and can deliver up to 30A to the load by the help of the TIP2955 pass transistors. Each transistor can handle up to 5A and six of them result an total output current of 30A. You can increase or reduce the number of TIP2955s to get higher or lower current outputs.
In this design the IC delivers about 800mA. A 1 amp fuse is connected after the LM7812 to protect the IC against high current transients.
The transistors and the 12V regulator IC both require adequate heatsinking. When the load current is high, the power dissipation of each transistor also increases so excess heat may cause the transistors to fail. Then you will need a very large heatsink or fan cooling.
100Ω resistors are used for stability and prevent current swamping as the tolerances of dc current gain will be different for each transistor.
The bridge rectifier diodes must be capable of passing at least 100 amps.
Posted on Wednesday, May 25, 2011 • Category: Arduino
Arduino Sine wave Generator using the direct digital synthesis Method.
Here we describe how to generate sine waves with an Arduino board in a very accurate way. Almost no additional hardware is required. The frequency range reaches form zero to 16 KHz with a resolution of a millionth part of one Hertz! Distortions can be kept less than one percent on frequencies up to 3 KHz. This technique is not only useful for music and sound generation another range of application is test equipment or measurement instrumentation. Also in telecommunication the DDS Method is useful for instance in frequency of phase modulation (FSK PSK).
The DDS Method (digital direct synthesis).
To implement the DDS Method in software we need four components. An accumulator and a tuning word which are in our case just two long integer variables, a sinewave table as a list of numerical values of one sine period stored as constants, a digital analog converter which is provided by the PWM (analogWrite) unit, and a reference clock derived by a internal hardware timer in the atmega. To the accumulator , the tuning word is added, the most significant byte of the accu is taken as address of the sinetable where the value is fetched and outputted as analog value bye the PWM unit. The whole process is cycle timed by an interrupt process which acts as the reference clock. Further details of the DDS Method are described in web of course.
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