Fading Red Eyes

Published:2012/10/22 1:07:00 Author:muriel | Keyword: Fading, Red Eyes | From:SeekIC

This circuit is used to slowly illuminate and fade a pair of redLEDs (light emitting diodes). The fading LEDs could be installedas 'eyes' in a small pumpkin or skull as a Halloween attraction,or mounted in a Christmas tree ornament. Or, they might be usedas a fancy power indicator for your computer, microwave oven,stereo system, TV, or other appliance.In operation, a linear 3 volt (peak to peak) ramping waveform isgenerated at pin 1 of the LM1458 IC and buffered with an emitter followertransistor stage. The 22uF capacitor and 47K resistor connected topin 2 establish the frequency which is about 0.5 Hz. You can make therate adjustable by using a 100K potentiometer in place of the 47Kresistor at pin 2.The circuit consists of two operational amplifiers (opamps),one producing a slow rising and falling voltage from about 3 volts to6 volts, and the other (on the right) is used as a voltage comparator,the output of which supplies a alternating voltage switching between2 and 7 volts to charge and discharge the capacitor with a constantcurrent.



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