Case #86: Bill Had That Weird Sensation He Was Being Watched

June 26, 2006

Partial to things that go bump in the night, Bill built a circuit that slowly illuminates and fades a pair of red LEDs. It consists of two op amps, one producing a slow rising and falling voltage (3 - 6V) and the other functioning as a voltage comparator. In operation, a linear 3V ramping waveform is generated at pin 1 of the LM1458 IC and buffered with an emitter follower transistor stage. Make the rate adjustable by using a 100K potentiometer in place of the 47K resistor at pin 2. Install it in a skull as a Halloween prop or if spooky things aren't your thing, use it as a fancy power indicator for a home appliance.

For Bill Bowden's complete instructions to build your own Fading Red Eyes circuit, go to

click here

"Fading Red Eyes" Parts List
Amt Part Description Allied Part #
2 Operational Amplifier LM1458 288-1090
4 4K Resistor 296-2182
1 100K Resistor 296-5610
1 100 ohms Resisistor 895-0465
1 Transistor 2N3904 568-8253
1 22 muF Capacitor 852-6516
1 Solderless Breadboard 237-0015
2 Red LED 670-1224
Additional parts required: 9V Battery

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