Led circuits

Quick view of Low battery indicators with LED

For a transistor to conduct, it requires a voltage of about 0.6 between its base and emitter. This voltage is applied from the wiper of the 47K pot. Now if the pot is at minimum, this voltage is across the 22K, so the 47K will have about 1.28v across it - or 1.88 across the pair. Add the 3V9 from the zener: this will require a battery voltage of 5.78v to just turn on the first transistor. Above 5.78 the right hand transistor is turned on, the left hand is therefore off and the LED is also off. Below 5.78v the LED will therefore come on...

Data Switch with LED

Data Switch with LED

Just to prove that transistors can also be useful in logic situations; this is a data latch and indicator which also is a data switch and has a bidirectional input/output port which can be read or switched. If the second transistor is off, a small currrent will flow via the LED, 12K and 220K to make Tr1 conduct, keeping Tr2 off. At the same time, the 4n7 charges up. ..

Audio 10 LED VU meter

Audio 10 LED VU meter

The circuit was designed to work with an audio power amplifier which operated off +18v-0v-18v power rails. The actual voltage used is not too critical except that the feedback is referred to the LED chain which itself is anchored to a +12v rail, hence the separate stabilizer for this. It has one large advantage over most of the LED chips available - all the LEDs are in series so it only draws 20mA irrespective of the number of LEDs illuminated. The two input op-amps form a rectifier circuit to rectify the audio input level. The changeover switch converts the circuit from average reading to peak reading...

Room thermometer with LEDs

Room thermometer with LEDs

This circuit uses a germanium diode (marked Ge) as a temperature sensor. I used an OA90 diode but others should do. The 'ring' of Tr1 and Tr2 bias each other. Tr1's collector current is stabilized by the 5v6 zener, causing Tr2 to operate at about 5mA: this collector current flows through the LED to generate about 1.5v bias for Tr1 so the current through the Ge diode is stabilized. The voltage across the diode will depend on its leakage current and you may need to alter the 1K5 to get a sensible range with a different diode. The voltage across the diode is inverted by the first 'op-amp' (in fact one section of an LM339 comparator used as an op-amp) to drive the LED line, shown in the pecked box. This LED line has been explained elsewhere on 4QD's pages, but it is biased at constant current by Tr3...

80x32 LED matrix display

80x32 LED matrix display

I recently purchased 10 SLM1608 (SLM1606) LED matrix display units from Ebay (you might also contact the seller directly at op16@gmx.de). These are 16x16 LED matrix units with a green and a red LED per pixel allowing each pixel to be switched to either green, red, amber or off. The goal of this LEDMATRIX project was to build a 80x32 pixel display by arranging the displays in two rows with 5 displays each giving a total of 16*16*2*2*5 = 5120 LEDs to be controlled individually. Fortunately these displays come with interated controllers and the data can be shifted into a single display using as few as 6 digital signals. By multiplexing some of the select signals all 10 displays can be controlled with a total of ten wires. Using a cheap ATmega32 microcontroller all ten displays can easily be controlled and updated in real time...

200 LEDs Christmas Lights circuit

200 LEDs Christmas Lights circuit

This simple and inexpensive circuit built around a popular CMOS hex inverter IC CD4069UB offers four sequential switching outputs that may be used to control 200 LEDs (50 LEDs per channel), driven directly from mains supply. Input supply of 230V AC is rectified by the bridge rectifiers D1 to D4. After fullwave rectification, the average output voltage of about 6 volts is obtained across the filter comprising capacitor C1 and resistor R5. This supply energises IC CD4069UB...

LED Christmas Star

LED Christmas Star

This circuit can be used to construct an attractive Christmas Star. When we switch on this circuit, the brightness of lamp L1 gradually increases. When it reaches the maximum brightness level, the brightness starts decreasing gradually. And when it reaches the minimum brightness level, it again increases automatically. This cycle repeats. The increase and decrease of brightness of bulb L1 depends on the charging and discharging of capacitor C3. When the output of IC1 is high, capacitor C3 starts discharging and consequently the brightness of lamp L1 decreases. IC2 is an opto-isolator whereas IC1 is configured as an astable multivibrator. The frequency of IC1 can be changed by varying the value of resistor R2 or the value of capacitor C1...

LED Running message Board CD4017

LED Running message Board CD4017

Light emitting diodes are advan- tageous due to their smaller size, low current consumption and catchy colours they emit. Here is a running message display circuit wherein the letters formed by LED arrangement light up progressively. Once all the letters of the message have been lit up, the circuit gets reset. The circuit is built around Johnson decade counter CD4017BC (IC2). One of the IC CD4017BEs features is its provision of ten fully decoded outputs, making the IC ideal for use in a whole range of sequencing operations. In the circuit only one of the outputs remains high and the other outputs switch to high state successively on the arrival of each clock pulse. The timer NE555 (IC1) is wired as a 1Hz astable multivibrator which clocks the IC2 for sequencing operations. ..

Dancing LED's circuit

Dancing LED's circuit

Here is a simple circuit which can be used for decoration purposes or as an indicator. Flashing or dancing speed of LEDs can be adjusted and various dancing patterns of lights can be formed. The circuit consists of two astable multivibrators. One multivibrator is formed by transistors T1 and T2 while the other astable multivibrator is formed by T3 and T4. Duty cycle of each multivibrator can be varied by changing RC time constant. This can be done through potentiometers VR1 and VR2 to produce different dancing pattern of LEDs...

LED Flasher with 555

LED Flasher with 555

This is a very basic circuit for flashing one or more LEDS and also to alternately flash one or more LEDs. It uses a 555 timer setup as an astable multivibrator with a variable frequency. With the preset at its max. the flashing rate of the LED is about 1/2 a second. It can be increased by increasing the value of the capacitor from 10uF to a higher value. For example if it is increased to 22uF the flashing rate becomes 1 second...

Water level alarm

Water level alarm

This circuit not only indicates the amount of water present in the overhead tank but also gives an alarm when the tank is full. The circuit uses the widely available CD4066, bilateral switch CMOS IC to indicate the water level through LEDs. When the water is empty the wires in the tank are open circuited and the 180K resistors pulls the switch low hence opening the switch and LEDs are OFF. As the water starts filling up, first the wire in the tank connected to S1 and the + supply are shorted by water. This closes the switch S1 and turns the LED1 ON...

Brakelight Stop flasher

Brakelight Stop flasher

This is basically a flasher circuit modified to turn on and off a bulb instead of a LED. It uses a 555 timer IC working as an astable multivibrator. The flashing rate can be varied from very fast to a maximum of once in 1.5 sec by varying the preset VR1...

LED Flasher IV

LED Flasher IV

This circuit will flash a string of LED's, typically 16, with direct connection to the mains and with a period adjustable between 1 and 4 seconds depending on the setting of the 22K/1W pot. Operation at 110V should also be possible but has not been tested. It can be used as a Christmas Tree decoration, entertainment in general or to flash a symbol made out of LED's - WARNING - this circuit is implemented at your own riisk! It operates directly out of the mains and proper precautions must be taken...

Solar Garden LED Lighting

Solar Garden LED Lighting

The circuit consists of two stages. The first stage is a "switch" or cut-off device. It detects a voltage above 0.7v from the solar panel and the resistance between its collector-emitter terminals reduces to a very small value. The 10k resistor allows the voltage on the solar panel to rise above 0.7v during bright sunlight, while the 100k discharges the 100p when the voltage is very low and the capacitor holds a charge to keep the transistor turned on when the voltage is "high". When the resistance between the collector-emitter terminals of the first transistor is low, it is turned ON, and the second transistor does not get enough voltage on its base for it to operate as an oscillator...

Robot Beacon with PIC12C508A

Robot Beacon with PIC12C508A

We hold the "first rights" to the presentation of this approach and the best part is: "It's FREE!" The PIC12C508A is one of the most amazing devices but because it does not come in a low-cost re-programmable form, it has never been presented in a "designers article." It is a one-time programmable device (OTP) and once it is programmed, it cannot be re-programmed. To develop with this chip is not an economical decision as it may take 30 to 100 modifications before you are completely happy with the operation of the software. That's 99 wasted chips! The only way to carry out experimentation is with the EPROM version (window version). These carry the part number PIC12C508A-JW and are about 10 times the cost of a normal PIC12C508A. ..

Sort List by: Alphabetic Date Clicks Rank ascending | descending

Neighbour Categories

Infrared	Lighting	Laser	LCD circuits
Xenon	Light Sensing	Fluorescent Circuits	Light Dimmers