Led circuits

This is the most simple phone busy indicator is possible with only three parts. Connect the circuit so that the green light illuminates when the line is free. If the receiver than the hook, the green LED light is weak. When connecting the red LED. ..

Diode Tester schematic

Diode Tester schematic

With this tester you can check whether a diode is working properly. In the table you can see what LED to indicate the positions of the switch and condition of the diode. The circuit can be connected to a 9 V battery...

LED Digital Thermometer schematic

LED Digital Thermometer schematic

This digital thermometer with 7 LEDs on the temperature measured with a NTC. The circuit works by using an opamp, the known 741 that the voltage difference between its positive and negative input strengthened. This gain (sensitivity) can be set P2. With P1, the bridge of P1 and R1 be adjusted...

Automotive voltage tester schematic

Automotive voltage tester schematic

This is a simple spanniningszoeker that is very suitable for car, for connection of alarm systems, handsfree kits, radios, etc. At rest, the yellow LED because the path of least resistance. If the probe with a positive or negative pole connected is coming and the red or green and yellow LED light goes out. The yellow LED also serves as a check or put pressure on the circuit state...

9V LED light organ

9V LED light organ

This is a nice example circuit that can be used at parties. The four LEDs blink to the beat of the music. The light organ using a microphone responds to sound. T1 amplifies the signal from MIC. The sensitivity can be adjusted with P1. T4 controls the LEDs. These are preferably high intensity LEDs. ..

LED Flasher IIV

LED Flasher IIV

This is a simple design of a single flashlight. This small circuit is within a half hour to build. The circuit operates from 4.5 to 12 V. Of course it is possible other than to drive an LED...

Astable multivibrator with two LED

Astable multivibrator with two LED

This is one of the basic circuitry of the electronics. The multivibrator astabiele shows two LEDs alternately light up with an adjustable speed. The circuit uses two transistors conduct alternately by the capacitors charged and discharged. The rate at which this happens depends on the capacity of capacitors of R2 and R3 and P1, and the load of the transistors...

Fet Led schematic

Fet Led schematic

This circuit uses the effect of a FET as the power to act through the gate with the source to connect. The voltage may vary between 4V and 30V, the current through the LED should constantly be around 15mA...

LED flasher with two transistors

LED flasher with two transistors

This circuit will flash a bright LED 5000mcd as an intention getting device or fake car alarm...

Fading LEDs schematic

Fading LEDs schematic

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. In operation, a linear 3 volt (peak to peak) ramping waveform is generated at pin 1 of the LM1458 IC and buffered with an emitter follower transistor stage. The 22uF capacitor and 47K resistor connected to pin 2 establish the frequency which is about 0.5 Hz. ..

1.5 volt LED flasher schematic

1.5 volt LED flasher schematic

This 1.5 volt led fasher runs more than a year on a single 'd" cell and alternately flashes 2 LEDs at about a 1 second rate. The circuit employs a 74HC14 CMOS hex inverter that will operate at very low voltages (less than 1 volt). One section is used as a squarewave oscillator (pins 1 and 2), while the others are wired to produce a short 10mS pulse on alternate edges of the square wave so the LEDs will alternate back and forth. The output sections each use a capacitor charge pump to increase the voltage for the LEDs. ..

Clock timer with LEDs

Clock timer with LEDs

This is a programmable clock timer circuit that uses individual LEDs to indicate hours and minutes. 12 LEDs can be arranged in a circle to represent the 12 hours of a clock face and an additional 12 LEDs can be arranged in an outer circle to indicate 5 minute intervals within the hour. 4 additional LEDs are used to indicate 1 to 4 minutes of time within each 5 minute interval. ..

Set reset flip-flop circuit

Set reset flip-flop circuit

This is an example of a set/reset flip flop using discrete components. When power is applied, only one of the transistors will conduct causing the other to remain off. ..

Photo detector using LED

Photo detector using LED

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. ..

25 LED Sequencer schematic

25 LED Sequencer schematic

This circuit is same as the above setup to drive 25 small Xmas lights. The lights operate at about 200mA and 3 volts. The supply voltage is set to 5 volts and the 4017 counter output will drop about a volt using the 2N3053 transistors. The voltage on the emitters of the rows transistors will be about 0.7 volts less than the base so the lamp voltage will be about 3 volts. You can adjust the supply voltage for the desired current if necessary. It works the same way as the LED version but you need diodes in series with each light. ..

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