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Nowadays you can buy white LEDs, which emit quite a bit of light. They are so bright that you shouldn’t look directly at them. They are still expensive, but that is bound to change. You can make a very good solid-state pocket torch using a few of these white LEDs. The simplest approach is naturally to use a separate series resistor for each LED, which has an operating voltage of around 3.5 V at 20 mA. Depending on the value of the supply voltage, quite a bit of power will be lost in the resistors. The converter shown here generates a voltage that is high enough to allow ten LEDs to be connected in series. In addition, this converter supplies a constant current instead of a constant voltage. A resistor in series with the LEDs produces a voltage drop that depends on the current through the LEDs. This voltage is compared inside the IC to a 1.25-V reference value, and the current is held constant at 18.4 mA (1.25 V ÷ 68 Ω). The IC used here is one of a series of National Semiconductor ‘sim

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circuit diagram: A total of four 1.2V cells are used here. Resistor R2 limits the charging current. For charging Li-ion battery (used in mobile phones), shift switches S1 and S2 to ‘on’ position and use connector ‘C.’ Regulator IC 7805 (IC2) provides 5V for charging the Li-ion battery. Using this circuit, you can charge a 3.6V Li-ion cell very easily. Resistor R3 limits the charging current. Fig. 2 shows the circuit for a small LED-based lamp. It is simple and low-cost. Six 10mm white LEDs (LED2 through LED7) are used here. Just connect them in parallel and drive directly by a 3.6V DC source. You can use either pencil-type Ni-Cd batteries or rechargeable batteries as the power source. Assemble the circuit on a general-purpose PCB and enclose in a small box. Mount RCA socket on the front panel of the box and wire RCA plug with cable for connecting the battery and LED-based lamp to the charger.

This is a simple project of Comparator Frequency LED Circuit Diagram. This Simple Comparator Frequency LED Circuit Diagram uses a comparison frequency IC 74HCT00, the device enabling frequency pulses are compared. Frequency F1 (signal frequency channel 1) and F2 (signal frequency channel 2). If the two frequencies are equal, then LED lights. Comperator Frequency LED Circuit Diagram Sourced By : Streampowers.blogspot.com

This Outdoor LED Solar Garden Lights project is a hobby circuit of an automatic garden light using a LDR and 6V/5W solar panel. During day time, the internal rechargeable 6 Volt SLA battery receives charging current from the connected solar panel through polarity protection diode D9 and current limiting resistor R10. If ambient light is normal, transistor T1 is reverse biased by IC1 (LM555). Here IC1 is wired as a medium current inverting line driver, switched by an encapsulated light detector (10mm LDR). Multi-turn trimpot P1 sets the detection sensitivity. When ambient light dims, transistor T1 turns on to drive the white LED string (D1-D8). Now this lamp load at the output of T1 energizes. Resistors R1-R8 limits the operating current of the LEDs. When the ambient light level restores, circuit returns to its idle state and light(s) switched off by the circuit. Outdoor Garden Solar Lights Circuit Diagram Assemble the Outdoor Solar Lights circuit on a general purpose PCB and enclose t

This circuit, designed on request, has proven to be useful to indicate when the voltage in a power supply line is changing from 120V to 240Vac. It can be used in different circumstances and circuits, mainly when an increase in ac or dc supply voltage needs to be detected. D3 illuminates when the line voltage is approaching 120V and will remain in the on state also at 240V supply. On the other hand, D6 will illuminate only when the line voltage is about 240V and will stay on because the latching action of Q1, Q2 and related components. C1, D1 and D2 provide a low dc voltage in the 4.5V - 6V range in order to allow proper operation of latch circuit and LEDs. Circuit diagram   Parts: R1_____________470R 1/2W Resistor R2_____________220K 1/4W Resistor R3,R7__________470R 1/4W Resistors R4_______________1K 1/4W Resistor R5_______________2K2 1/4W Resistor R6_____________330R 1/4W Resistor C1_____________330nF 630V Polyester Capacitor C2______________10µF 25V Electrolytic Capacitor D1,D2_____

The 555 circuit below is a flashing bicycle light powered with four C,D or AA cells (6 volts). Two sets of 20 LEDs will alternately flash at approximately 4.7 cycles per second using RC values shown (4.7K for R1, 150K for R2 and a 1uF capacitor). Time intervals for the two lamps are about 107 milliseconds (T1, upper LEDs) and 104 milliseconds (T2 lower LEDs). Two transistors are used to provide additional current beyond the 200 mA limit of the 555 timer. A single LED is placed in series with the base of the PNP transistor so that the lower 20 LEDs turn off when the 555 output goes high during the T1 time interval. The high output level of the 555 timer is 1.7 volts less than the supply voltage. Adding the LED increases the forward voltage required for the PNP transistor to about 2.7 volts so that the 1.7 volt difference from supply to the output is insufficient to turn on the transistor. Each LED is supplied with about 20mA of current for a total of 220mA. The circuit should work with

You might have seen a " Hello World! " program code example while learning some programming language. While it is useful for getting familiar with the basics of that language, it also gives you a head start in that environment. If you ever want to learn some new programming language, you might want to Google out a "Hello world!' program code to get started. The code I am about to discuss serves the same purpose for the 8051 microcontroller because it is the most simplest task to perform. Play close attention if you want everything to work properly. READ MORE

Signals when an on-circuit battery is exhausted 5V to 12V operating voltage. A Battery-status Indicator circuit can be useful, mainly to monitor portable Test-gear instruments and similar devices. LED D1 flashes to attire the user's attention, signaling that the circuit is running, so it will not be left on by mistake. The circuit generates about two LED flashes per second, but the mean current drawing will be about 200µA. Transistors Q1 and Q2 are wired as an uncommon complementary astable multivibrator: both are off 99% of the time, saturating only when the LED illuminates, thus contributing to keep very low current consumption. Flashing-LED Battery-status Indicator Circuit diagram : Flashing-LED Battery-status Indicator Circuit Diagram The circuit will work with battery supply voltages in the 5 - 12V range and the LED flashing can be stopped at the desired battery voltage (comprised in the 4.8 - 9V value) by adjusting Trimmer R4. This range can be modified by changing R3 and/or

Only a few years ago, the choice of LED s was limited to IR, red, yellow, and green. The LED manufacturers have been busy extending the spectrum, and filling in the gaps. The latest generation of organic LED s (OLEDs) has added some dazzling new colors to the spectrum. This circuit uses a set of 13 differently colored LED s to generate a full color spectrum. The photo does not fully represent the colors generated due to camera limitations. The real-world display is very eye-catching. If you want to "trick out" your PC, this circuit is for you. Forget about those boring blue PC light displays. Specifications: Operating Voltage: 6-12V DC Operating Current: 145ma at 12V DC Theory: The LM2940T-5.0 low dropout voltage regulator converts the 6-12V DC input power to regulated 5 Volts. It was chosen over a standard 7805 regulator so that the circuit could maintain regulation while operating on a 6V battery. The 1N4001 diode protects the circuit from reverse polarity, if a battery or

Nowadays you can buy white LEDs, which emit quite a bit of light. They are so bright that you shouldn’t look directly at them. They are still expensive, but that is bound to change. You can make a very good solid-state pocket torch using a few of these white LEDs. The simplest approach is naturally to use a separate series resistor for each LED, which has an operating voltage of around 3.5 V at 20 mA. Depending on the value of the supply voltage, quite a bit of power will be lost in the resistors. The converter shown here generates a voltage that is high enough to allow ten LEDs to be connected in series. In addition, this converter supplies a constant current instead of a constant voltage. A resistor in series with the LEDs produces a voltage drop that depends on the current through the LEDs. This voltage is compared inside the IC to a 1.25-V reference value, and the current is held constant at 18.4 mA (1.25 V ÷ 68 Ω). The IC used here is one of a series of National Semiconductor ‘sim

The process mentioned below shows how we can convert the LEDs to the light sensors so that it can be used for many other purposes also. Read on to know more about this.As the Blinkenlight Shield has 20 of them, 20 pixel camera can be developed by it. After performing the experiment, it is recommended to reset the jumper setting to default. LED or Light Emitting diodes usually act as the photo diodes and are optimized to produce the light. LEDs can be used to make the light detectors that can be helpful in various conditions. The idea behind this is to reverse bias the diodes by turning the IO pins to output low so that the LEDs used will act as capacitors and will not be conducted. The current produced due to the LED is very small, and the photo current produced discharges the LED capacitors. After charging, the IO pins have to be switched to high Z so as to generate the light. The light produced and the current are directly proportional to each other. After the discharging of capacito

It is not always necessary to use special photoresistors or phototransistors to make light-sensitive switches. Although it is not well known, normal visible-light and infrared LEDs will also work. A voltage that depends on the intensity of the natural or artificial illumination falling on the LED can be taken from the anode of the LED. This behaviour can be easily verified by connecting a DVM or oscilloscope directly to the two leads of the LED. Circuit Diagram: LED Photosensor Circuit Diagram Since the load on the photoelectric potential should be kept as small as possible, a JFET is used here as a buffer. The type used is not critical; similar transistors should work equally well. The buffered voltage is fed to the inverting input of comparator IC1. The threshold voltage can be adjusted to meet the desires of the user by means of the potentiometer. A pull-up resistor is connected to the com-parator output, since the LM393 has an open-collector out-put. The supply voltage may be c

Nowadays you can buy white LEDs, which emit quite a bit of light. They are so bright that you shouldn’t look directly at them. They are still expensive, but that is bound to change. You can make a very good solid-state pocket torch using a few of these white LEDs. The simplest approach is naturally to use a separate series resistor for each LED, which has an operating voltage of around 3.5 V at 20 mA. Depending on the value of the supply voltage, quite a bit of power will be lost in the resistors. The converter shown here generates a voltage that is high enough to allow ten LEDs to be connected in series. In addition, this converter supplies a constant current instead of a constant voltage. A resistor in series with the LEDs produces a voltage drop that depends on the current through the LEDs. This voltage is compared inside the IC to a 1.25-V reference value, and the current is held constant at 18.4 mA (1.25 V ÷ 68 Ω). The IC used here is one of a series of National Semiconductor ‘sim

LED Photo sensor Circuit Diagram. It is not always necessary to use special photoresistors or phototransistors to make light-sensitive switches. Although it is not well known, normal visible-light and infrared LEDs will also work. A voltage that depends on the intensity of the natural or artificial illumination falling on the LED can be taken from the anode of the LED. This behaviour can be easily verified by connecting a DVM or oscilloscope directly to the two leads of the LED. LED Photo sensor Circuit Diagram: LED Photosensor Circuit Diagram Since the load on the photoelectric potential should be kept as small as possible, a JFET is used here as a buffer. The type used is not critical; similar transistors should work equally well. The buffered voltage is fed to the inverting input of comparator IC1. The threshold voltage can be adjusted to meet the desires of the user by means of the potentiometer. A pull-up resistor is connected to the com-parator output, since the LM393 has an open

This is a 555 led flasher circuit this circuit will blink many LEDs and give rotating effects. The circuit is very easy to build, 555 timer IC is very common now a days you will find it easily. The circuit uses only 3 volt to perform its task, small 3 volt button cells can also be used and it will last longer because the circuit has low current consumption. Upper 555 IC in the circuit is used as multivibrator and the lower 555 IC is working as a trigger pulse inverter.  Source http://www.circuitdiagram.org

This simple LED flasher using transistor,  an LED flasher can be made ​​that can be used for example to simulate the existence of an alarm mounted in a vehicle driver. LED Flasher Using Transistor Circuit Diagram: The circuit is a relaxation oscillator built around transistor T1 Unijunction that provides repeated pulses with a duration of a few milliseconds, Darlington transistor T2. When the contact is closed the LED is blocked through T3. The circuit has a current actual consumption of only 2 mA. Resistors R1 and R3 will be resized to compensate for higher tolerances resulting from manufactured Unijunction transistors. Do not use in the assembly of high power LEDs (current peaks should not exceed 250 mA).

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The 555 circuit below is a flashing bicycle light powered with four C,D or AA cells (6 volts). Two sets of 20 LEDs will alternately flash at approximately 4.7 cycles per second using RC values shown (4.7K for R1, 150K for R2 and a 1uF capacitor). Time intervals for the two lamps are about 107 milliseconds (T1, upper LEDs) and 104 milliseconds (T2 lower LEDs). Two transistors are used to provide additional current beyond the 200 mA limit of the 555 timer. Circuit diagram : 40 LED Bicycle Light Circuit Diagram A single LED is placed in series with the base of the PNP transistor so that the lower 20 LEDs turn off when the 555 output goes high during the T1 time interval. The high output level of the 555 timer is 1.7 volts less than the supply voltage. Adding the LED increases the forward voltage required for the PNP transistor to about 2.7 volts so that the 1.7 volt difference from supply to the output is insufficient to turn on the transistor. Each LED is supplied with about 20 mA o

The following display features eight 7-segment displays arranged in two rows of four digits. The on-board MAX7219 driver enables you to easily add eight 7-segment LED displays to your project using only 3 I/O pins of microcontroller. The major advantage of using this board is the time-division multiplexing operations required for continuous refreshing of the display digits are performed by the MAX7219 chip, thereby keeping the microcontroller free for doing other pressing tasks. It is suitable for displaying two variable values simultaneously in a project, such as displaying temperature and humidity, or current and voltage, etc. [ ]