Circuit Finder

16 Stage Bi-Directional LED Sequencer

Published on 2011-01-18 07:27:47

The bi-directional sequencer uses a 4 bit binary up/down counter (CD4516) and two "1 of 8 line decoders" (74HC138 or 74HCT138) to generate the popular "Night Rider" display. A Schmitt Trigger oscillator provides the clock signal for the counter and the rate can be adjusted with the 500K pot.

10 Channel LED Sequencer

Published on 2011-01-18 07:26:38

10 Channel LED Sequencer

18 Stage LED Sequencer

Published on 2011-01-18 07:25:00

When power is applied, the 15K resistor and 10uF cap at pin 15 will reset the counters to the zero count where pin 3 is at +12 and all other outputs are at zero. The 2 diodes (1n914) and 15 resistor form a AND gate so the clock pulse will be passed to the right side counter when the sequence starts.

Two Transistor LED Flasher

Published on 2011-01-18 07:21:10

Two Transistor LED Flasher

1.5 Volt LED Flashers

Published on 2011-01-18 07:20:00

The LED flasher circuits below operate on a single 1.5 volt battery. The circuit on the upper right uses the popular LM3909 LED flasher IC and requires only a timing capacitor and LED.

LED Photo Sensor.

Published on 2011-01-16 07:20:40

Here's a circuit that takes advantage of the photo-voltaic voltage of an ordinary LED. The LED voltage is buffered by a junction FET transistor and then applied to the inverting input of an op-amp with a gain of about 20. This produces a change of about 5 volts at the output from darkness to bright light. The 100K potentiometer can be set so that the output is around 7 volts in darkness and falls to about 2 volts in bright light.

Fading Red Eyes

Published on 2011-01-16 07:19:12

This circuit is used to slowly illuminate and fade a pair of red LEDs (light emitting diodes). The fading LEDs could be installed as 'eyes' in a small pumpkin or skull as a Halloween attraction, or mounted in a Christmas tree ornament. Or, they might be used as a fancy power indicator for your computer, microwave oven, stereo system, TV, or other appliance.

Automatic 12 Volt Lamp Fader

Published on 2011-01-16 07:15:10

This circuit is similar to the "Fading Red Eyes" circuit (in the LED section) used to fade a pair of red LEDs. In this version, the lamps are faded by varying the duty cycle so that higher power incandescent lamps can be used without much power loss. The switching waveform is generated by comparing two linear ramps of different frequencies.

LED 12 Volt Lead Acid Battery Meter

Published on 2011-01-16 07:13:21

In the circuit, a quad voltage comparator (LM339) is used as a simple bar graph meter to indicate the charge condition of a 12 volt, lead acid battery. A 5 volt reference voltage is connected to each of the (+) inputs of the four comparators and the (-) inputs are connected to successive points along a voltage divider. The LEDs will illuminate when the voltage at the negative (-) input exceeds the reference voltage.

AC Line powered LEDs

Published on 2011-01-16 07:12:03

The circuit below illustrates powering a LED (or two) from the 120 volt AC line using a capacitor to drop the voltage and a small resistor to limit the inrush current. Since the capacitor must pass current in both directions, a small diode is connected in parallel with the LED to provide a path for the negative half cycle and also to limit the reverse voltage across the LED. A second LED with the polarity reversed may be subsituted for the diode, or a tri-color LED could be used which would appe