Brightness Controller Circuit For Small Lamps and Leds

Description 

 This device was designed on request; to control the light intensity of four filament lamps (i.e. a ring illuminator) powered by two AA or AAA batteries, for close-up pictures with a digital camera. Obviously it can be used in other ways, at anyone's will.IC1 generates a 150Hz square wave having a variable duty-cycle. When the cursor of P1 is fully rotated towards D1, the output positive pulses appearing at pin 3 of IC1 are very narrow.

Bulb LP1, driven by Q1, is off as the voltage across its leads is too low. When the cursor of P1 is rotated towards R2, the output pulses increase in width, reaching their maximum amplitude when the potentiometer is rotated fully clockwise. In this way the bulb reaches its full brightness.

Circuit Diagram:

Parts:

• P1 = 470K
• R1 = 10K
• R2 = 47K
• R3 = 1.5K
• C1 = 22nF-63V
• C2 = 100uF-25V
• D1 = 1N4148
• D2 = 1N4148
• Q1 = BD681
• B1 = 2xAA cells in series
• IC1 = 7555 or TS555CN
• LP1 = 1.5V 200mA Bulb
• SW1 = SPST Switch 

Notes: 

• LP1 can be one or more 1.5V bulbs wired in parallel. Maximum total output current allowed is about 1A.
• R2 limits the output voltage, measured across LP1 leads, to 1.5V. Its actual value is dependent on the total current drawn by the bulb(s) and should be set at full load in order to obtain about 1.5V across the bulb(s) leads when P1 is rotated fully clockwise. 

 Source http://www.extremecircuits.net/2009/08/brightness-controller-circuit-for-small.html  

07:17 0 comments

Line Powered White LEDs

Description 

The LED circuit below is an example of using 25 white LEDs in series connected to the 120VAC line. It can be modified for more or less LEDs by adjusting the resistor value. The exact resistance will depend on the particular LEDs used. But working out the resistor value is a bit complicated since current will not continously flow through the resistor. In operation, the output of the bridge rectifier will be about 120 DC RMS or 170 volts peak. If we use 25 white LEDs with a forward voltage of 3 volts each, the total LED voltage will be 75 volts. The peak resistor voltage will be 170- 75 or 95 volts but the resistor voltage will not be continous since the input must rise above 75 before any current flows. This (dead time) represents about 26 degrees of the 90 degree half wave rectified cycle, (asin) 75/170 = (asin) .44 = 26 degrees. This means the resistor will conduct during 90-26 = 64 degrees, or about 71 percent of the time.

Next we can work out the peak LED current to determine the resistor value. If the LED current is 20mA RMS, the peak current will be 20*1.414 or 28mA. But since the duty cycle is only 71 percent, we need to adjust this figure up to 28/0.71 = 39mA. So, the resistor value should be 95/.039 = 2436 ohms (2.4K) and the power rating will be .02^2 *2400= .96 watts. A two watt size is recommended.

Now this circuit can also be built using 2 diodes and resistor as shown in the lower drawing. The second diode in parallel with the LEDs is used to avoid a reverse voltage on the LEDs in case the other diode leaks a little bit. It may not be necessary but I thought it was a good idea.

Working out the resistor value is similar to the other example and comes out to about half the value of the full wave version, or about 1.2K at 1 watt in this case. But the peak LED current will be twice as much or about 78mA. This is probably not too much, but you may want to look up the maximum current for short duty cycles for the LEDs used and insure 79mA doesn't exceed the spec.

Circuit Diagram 

Source http://www.bowdenshobbycircuits.info/

09:22 0 comments

16 Stage Bi-Directional LED Sequencer Circuit

Description 

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. Two additional Schmitt Trigger inverters are used as a SET/RESET latch to control the counting direction (up or down). Be sure to use the 74HC14 and not the 74HCT14, the 74HCT14 may not work due to the low TTL input trigger level. When the highest count is reached (1111) the low output at pin 7 sets the latch so that the UP/DOWN input to the counter goes low and causes the counter to begin decrementing. When the lowest count is reached (0000) the latch is reset (high) so that the counter will begin incrementing on the next rising clock edge. The three lowest counter bits (Q0, Q1, Q2) are connected to both decoders in parallel and the highest bit Q3 is used to select the appropriate decoder. The circuit can be used to drive 12 volt/25 watt lamps with the addition of two transistors per lamp as shown below in the section below titled "Interfacing 5 volt CMOS to 12 volt loads" 

Circuit Diagram

 Source -http://www.bowdenshobbycircuits.info/

09:14 0 comments

Smooth Flasher Circuit Diagram

Circuit Diagram:

Description

Ordinary LED flashers turn the LED on and off abruptly, which can get a little irritating after a while. The circuit shown here is more gentle on the eyes: the light intensity changes very slowly and sinusoidally, helping to generate a relaxed mood. The circuit shows a phase-shift oscillator with an adjustable current source at its output. The circuit is capable of driving two LEDs in series without affecting the current.

The frequency is set by three RC networks, each of which consists of a 100 µF capacitor and a 22 kO resistor. Operation is largely independent of supply voltage, and the average LED current is set at about 10 mA. The circuit adjusts the voltage across the emitter resistor so that it matches the base voltage of the first transistor (around 0.6 V). The phase shifting network gives rise to the oscillation around this average value. In the prototype of this circuit we used an ultra-bright red LED. 

Author: Burkhard Kainka, Elektor Electronics 2008
Source http://www.extremecircuits.net/2010/05/smooth-flasher-circuit-diagram.html

08:18 0 comments

18 Stage LED Sequencer Circuit

Description 

The question sometimes comes up of how to cascade 4017 decade counters for more than 10 sequencial stages. The LED sequencer below shows a possible solution using a few extra parts.

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. When the right counter reaches the 10th count, pin 11 will move high enabling the AND gate on the right to pass the clock pulse to the left side counter. As the left side counter advances, pin 3 will be low so that clock pulses cannot advance the right counter. When the left counter turns over and pin 3 again moves high, the sequence will repeat. Thus we get 18 total counts, 9 from the first counter, and 9 from the second.

Circuit Diagram

 Note that the 4017 counter will not deliver much current, and so the LED current is set to about 6mA using a 1.5K resistor in series. For more current, you could use transistors on each output as shown in the drawing above, (10 Channel LED Sequencer). But some of the newer bright LEDs are fairly bright at 6mA.

06:14 0 comments

AC Line powered LEDs Circuit

Description 

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 appear orange with alternating current. The circuit is fairly efficient and draws only about a half watt from the line. The resistor value (1K / half watt) was chosen to limit the worst case inrush current to about 150 mA which will drop to less than 30 mA in a millisecond as the capacitor charges. This appears to be a safe value, I have switched the circuit on and off many times without damage to the LED. The 0.47 uF capacitor has a reactance of 5600 ohms at 60 cycles so the LED current is about 20 mA half wave, or 10 mA average. A larger capacitor will increase the current and a smaller one will reduce it. The capacitor must be a non-polarized type with a voltage rating of 200 volts or more.

The lower circuit is an example of obtaining a low regulated voltage from the AC line. The zener diode serves as a regulator and also provides a path for the negative half cycle current when it conducts in the forward direction. In this example the output voltage is about 5 volts and will provide over 30 milliamps with about 300 millivolts of ripple. Use caution when operating any circuits connected directly to the AC line.

Circuit Diagram

 Source -  http://www.bowdenshobbycircuits.info/

11:11 0 comments

Automatic 12 Volt Lamp Fader Circuit

Description

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. The higher frequency ramp waveform (about 75 Hz.) is produced from one section of the LM324 quad op-amp wired as a Schmitt trigger oscillator. The lower frequency ramp controls the fading rate and is generated from the upper two op-amps similar to the "fading eyes" circuit. The two ramp waveforms at pins 9 and 1 are compared by the 4th op-amp which generates a varying duty cycle rectangular waveform to drive the output transistor. A second transistor is used to invert the waveform so that one group of lamps will fade as the other group brightens. The 2N3053 will handle up to 500 milliamps so you could connect 12 strings of 4 LEDs each (48 LEDs) with a 220 ohm resistor in series with each group of 4 LEDs. This would total about 250 milliamps. Or you can use three 4 volt, 200 mA Xmas tree bulbs in series. For higher power 12 volt automobile lamps, the transistor will need to be replaced with a MOSFET that can handle several amps of current. See the drawing below the schematic for possible hookups.

Circuit Diagram

 

Other Possible Hookups

 

 Source - http://www.bowdenshobbycircuits.info/

06:37 0 comments

Sunrise Lamp Circuit

Circuit Diagram 

Description

In this circuit, a 120VAC lamp is slowly illuminated over a approximate 20 minute period. The bridge rectifier supplies 120 DC to the MOSFET and 60 watt lamp. A 6.2K, 5 watt resistor and zener diode is used to drop the voltage to 12 volts DC for the circuit power. The bridge rectifier should be rated at 200 volts and 5 amps or more. In operation, a 700 Hz triangle waveform is generated at pin 1 of the LM324 and a slow rising voltage is obtained at pin 8. These two signals are compared at pins 12 and 13 to produce a varying duty cycle rectangular waveform at pin 14, which controls the MOSFET and brightness of the 60 watt lamp. When power is applied, the lamp will start to illuminate within a minute or so, and will slowly brighten to full intensity in about 20 minutes. You can make that longer or shorter with adjustments to the 270K resistor at pin 9. The 2.2 ohm resistor and .015uF cap connected to the lamp serve to supress RFI. The diode at pin 9 and 10K resistor on pin 8 are used to discharge the 3300uF cap when power is removed. Power should be off for a few minutes before re-starting.

Caution: This circuit is connected directly to the AC line and presents a hazard if any part is touched while connected to the line. Use caution and do not touch any parts while the circuit is connected to the AC line. You may want to use a 9 volt battery connected across the 12 volt zener to check the basic operation. The DC voltage at pins 1,2,3,5,6,7 will all be around 4.3 volts if the circuit is working correctly. If the DC voltages are all correct, you can use a variac to slowly apply the full line voltage and check for proper operation.

Source- http://www.bowdenshobbycircuits.info/

06:15 0 comments

Two-Led Pilot Light Circuit

Description 
This circuit is designed on request and can be useful to those whishing to have, say, a red LED illuminated when an appliance is on and a green LED illuminated when the same appliance is off. Any mains operated appliance can be monitored by this circuit provided a suitable mains switch, capable of withstanding the full load current, is used for SW1.When SW1 is closed, the load and D4 are energized, Q1 is saturated and shorts D3, thus preventing its illumination.
Circuit Diagram:

Parts:

• R1 = 27K-1W
• R2 = 27K-1W
• R3 = 6.8K
• D1 = 1N4007
• D2 = 1N4007
• D3 = Green
• D4 = Red Led
• Q1 = BC337
• SW1 = SPST Mains Switch

Notes:

• Change R1 and R2 to 15K 1W for 115Vac mains operation.
• SW1 must be capable of withstanding the appliance's full load current and volage

Source-http://www.redcircuits.com/#home

06:58 0 comments

1.5 Volt LED Flashers Circuit

Description 

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.

The top left circuit, designed by Andre De-Guerin illustrates using a 100uF capacitor to double the battery voltage to obtain 3 volts for the LED. Two sections of a 74HC04 hex inverter are used as a squarewave oscillator that establishes the flash rate while a third section is used as a buffer that charges the capacitor in series with a 470 ohm resistor while the buffer output is at +1.5 volts. When the buffer output switches to ground (zero volts) the charged capacitor is placed in series with the LED and the battery which supplies enough voltage to illuminate the LED. The LED current is approximately 3 mA, so a high brightness LED is recommended.

In the other two circuits, the same voltage doubling principle is used with the addition of a transistor to allow the capacitor to discharge faster and supply a greater current (about 40 mA peak). A larger capacitor (1000uF) in series with a 33 ohm resistor would increase the flash duration to about 50mS. The discrete 3 transistor circuit at the lower right would need a resistor (about 5K) in series with the 1uF capacitor to widen the pulse width.

Circuit Diagram

Source -  http://www.bowdenshobbycircuits.info/

07:17 0 comments

IC Controlled Emergency Light With Charger Circuit Diagram

Circuit Diagram: 

Description

Here is the circuit diagram of IC Controlled Emergancy Light With Charger or simply 12V to 220V AC inverter circuit. The circuit shown here is that of the IC controlled emergency light. Its main features are: automatic switching-on of the light on mains failure and battery charger with over-charge protection. When mains is absent, relay RL2 is in de-energized state, feeding battery supply to inverter section via its N/C contacts and switch S1.

The inverter section comprises IC2 (NE555) which is used in stable mode to produce sharp pulses at the rate of 50 Hz for driving the MOSFETs. The output of IC2 is fed to gate of MOSFET (Q4) directly while it is applied to MOSFET (Q3) gate after inversion by transistor Q2. Thus the power amplifier built around MOSFETs Q3 and Q4 functions in push-pull mode. The output across secondary of transformer T2 can easily drive a 230-volt, 20-watt fluorescent tube. In case light is not required to be on during mains failure, simply flip switch S1 to off position. Battery overcharge preventer circuit is built around IC1 (LM308).

Its non-inverting pin is held at a reference voltage of approximately 6.9 volts which is obtained using diode D5 (1N4148) and 6.2-volt zener D6. The inverting pin of IC1 is connected to the positive terminal of battery. Thus when mains supply is present, IC1 comparator output is high, unless battery voltage exceeds 6.9 volts. So transistor Q1 is normally forward biased, which energises relay RL1. In this state the battery remains on charge via N/O contacts of relay RL1 and current limiting resistor R2. When battery voltage exceeds 6.9 volts (overcharged condition), IC1 output goes low and relay RL1 gets de-energised, and thus stops further charging of battery. MOSFETs Q and Q4 may be mounted on suitable heat sinks. 

Parts:

• R1 = 1K
• R2 = 10R-1W
• R3 = 820R
• R4 = 1K
• R5 = 10K
• R6 = 1K
• R7 = 100R
• R8 = 1K
• C1 = 1000uF-25V
• C2 = 10uF-16V
• C3 = 0.01uF
• D1 = 1N4007
• D2 = 1N4007
• D3 = 1N4007
• D4 = 1N4007
• D5 = 1N4148
• D6 = 6.2V Zener
• D7 = 1N4007
• D8 = 1N4148
• Q1 = SL100
• Q2 = 2N2222
• Q3 = IRF840
• Q4 = IRF840
• IC1 = LM308
• IC2 = NE555
• S1 = SPST Switch
• B1 = 6V-4A Battery
• B2 = 6V-4A Battery
• TI = 220V AC Primary to 0V-6V 250mA Secondary Transformer
• T2 = 4.5V-0V-4.5V 5A Primary To 230V AC Secondary Transformer 

Source - http://www.extremecircuits.net/2010/01/ic-controlled-emergency-light-with.html

07:18 0 comments

Fading Red Eyes Circuit

Description: 

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. You can make the rate adjustable by using a 100K potentiometer in place of the 47K resistor at pin 2.

The circuit consists of two operational amplifiers (opamps), one producing a slow rising and falling voltage from about 3 volts to 6 volts, and the other (on the right) is used as a voltage comparator, the output of which supplies a alternating voltage switching between 2 and 7 volts to charge and discharge the capacitor with a constant current.

Each of the op-amps has one of the inputs (pins 3 and 6) tied to a fixed voltage established by two 47K resistors so that the reference is half the supply voltage or 4.5 volts. The left opamp is connected as an inverting amplifier with a capacitor placed between the output (pin 1) and the inverting input (pin 2). The right opamp is connected as a voltage comparator so that the output on pin 7 will be low when the input is below the reference and high when the input is higher than the reference. A 100K resistor is connected between the comparator output and input to provide positive feedback and pulls the input above or below the switching point when the threshold is reached. When the comparator output changes at pin 7, the direction of the current changes through the capacitor which in turn causes the inverting opamp to move in the opposite direction. This yields a linear ramping waveform or triangle waveform at pin 1 of the inverting opamp. It is always moving slowly up or down, so that the voltage on the non-inverting input stays constant at 4.5 volts.

Adjustments to the point where the LEDs extinguish can be made by altering the resistor value at pin 3 and 6 to ground. I found a 56K in place of the 47k shown worked a little better with the particular LEDs used. You can experiment with this value to get the desired effect.

Parts List: 

• Description - Mfg Part# -Allied Part# - Quantity - Cost
• Operational Amplifier LM1458 - 288-1090 - 1 - .48
• 47K Resistor - 296-2182 - 4 - .42
• 100K Resistor - 296-5610 - 1
• 100 Ohm Resistor - 895-0465 - 1 - .24
• Transistor 2N3904 - 568-8253 - 1 - .1
• 22uF Capacitor - 852-6516 - 1 - .07
• Solderless Breadboard - 237-0015 - 1 - 6.99
• Red Light Emitting Diode (LED) - 670-1224 - 2 - 0.50

Note: The LED listed has a narrow viewing angle of 30 degrees and appears brightest when looking directly at it. It's not a pure red color, and a little on the orange side, but should be brighter compared to other selections. For a wider viewing angle at reduced intensity, try part number 670-1257 which is viewable at 60 degrees and has a red diffused lens.
Construction details:

 Layout of the solderless breadboard:

Refer to the drawing below the schematic diagram and note the solderless breadboard is arranged in rows labeled A-J, and columns numbered 1 to 65. Each group of 5 holes in the same column are the same connection, so that holes A1,B1,C1,D1 and E1 are all connected together. Likewise holes F1,G1,H1,I1 and J1 are all the same connection. The outer rows along the length of the board are also connected together and are normally used for power supply connections. However, there is a break in the mid section of the outer rows, so a short jumper wire connecting the mid section of the outer rows should be installed to connect the entire outer row together. If you have a DMM, use the low ohms range and probe the various holes to get familiar with the board layout.

Installing the components:

Orientate the LM1458 so the nook or punch mark on one edge is near column 30 and the opposite edge is near column 33. Install the LM1458 on the breadboard so the pins straddle the center section of the board and pin 1 of the IC is occupying hole E30 and pin 8 is in hole F30. The pins are numbered counter clockwise, so pin 4 will be occupying F33 and pin 5 will be in E33. Possible connections for the LM1458, 9 volt battery, and a couple other parts is illustrated in the lower drawing of the solderless breadboard, but it is not complete with all parts.

Refer to the schematic diagram, and install the various other components so they connect to the appropriate pins of the LM1458. Use whatever connection holes are convenient. For example, the 22uF capacitor connects between pins 1 and 2 of the IC, which occupy holes (F30,F31) so it could be placed in the holes (H30, H31) or (J30,J31) or (I30,I31). But not all parts will conveniently fit, so you may have to use a short jumper wire (#22 preferred) to connect parts from one side of the chip to the other.

The board I assembled was connected this way:

• LM1458 F30 to F33, and E30 to E33
• 22uF capacitor H30 to H31
• 47K resistor I30 to I35
• 47K resistor C27 to C31
• 47K resistor F25 to Positive battery row
• 47K resistor J25 to Negative Battery row
• 100K resistor B31 to B33
• 2N3904 Transistor G36, G37, G38 with emitter at G38
• 100 Ohm resistor D38 to F38
• LED B43 to B44 (Cathode at B44)
• LED I43 to I44 (Cathode at I43)
• Jumper A30 to Positive battery row
• Jumper F36 to Positive battery row
• Jumper J33 to Negative battery row
• Jumper J43 to Negative battery row
• Jumper H25 to J32
• Jumper J30 to J37
• Jumper E27 to G31
• Jumper D32 to G32
• Jumper D33 to H35
• Jumper C38 to C43
• Jumper E44 to F44
• 9 Volt Battery Postive battery row to negative row.

Circuit diagram

 The circuit below illustrates two pairs of LEDs that operate out of phase so as one pair slowly illuminate, the other pair will fade.

Source - http://www.bowdenshobbycircuits.info/

08:41 0 comments

Flashy Christmas Lights Circut

Description

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.

All gates (N1-N6) of the inverter have been utilised here. Gates N1 to N4 have been used to control four high voltage transistors T1 to T4 (2N3440 or 2N3439) which in turn drive four channels of 50 LEDs each through current limiting resistors of 10-kilo-o Base drive of transistors can be adjusted with the help of 10-kilo-ohm pots provided in their paths. Remaining two gates (N5 and N6) form a low frequency oscillator. The frequency of this oscillator can be changed through pot VR1. When pot VR1 is adjusted To get the best results, a low leakage, good quality capacitor must be used for the timing capacitor C2

Circuit Diagram

Source - http://electronic-circuits-diagrams.com/lightsimages/lightsckt9.shtml

08:53 0 comments

Electronic Dice Circuit Diagram

Description

With this electronic dice the result is displayed with LEDs that are placed so every dice face is shown. In the circuit diagram, IC 4022 is used to count to 6 in which only one output can get “1″ state.
A diode matrix (D1..D8) serve as decoding the output signals of the counter so that the LEDs are controlled by two buffer transistors and series resistance.

 Integrated circuit outputs only support a reduced load, so in the transistor’s base are connected the limiting resistances. As a clock generator it can be used any generator with rectangular pulses whose amplitude corresponds to the IC’s supply voltage. The 4022 clock input impedance is 10¹²Ω.

 Circuit Diagram

 Source - http://electroschematics.com/5011/electronic-dice/

10:45 0 comments

Automatic Light Dimmer Circut Diagram

Description

In many cases, the dimmer presented here may be built into a wall-mounted box containing the light switch. It is intended for use with 240 V incandescent lamps only. When it is fitted, and the light is switched on, the lamp does not come on fully for about 400 ms (which is not noticeable). When the light is switched off, it stays on unchanged for about 20 s, and then goes out gradually. This has the advantage that it is not immediately dark when the light is switched off. When light switch S1 is turned on, capacitor C2 is charged via R1, C1 and bridge rectifier D1–D4. Zener diode D5 limits the potential across C2 to about 15 V. After a short while, diode D6 lights, whereupon a potential difference ensues across light sensitive resistor R3, which is sufficient to trigger triac Tr1.

Circuit diagram:

 The light then comes on. When the light switch is turned off, C2 is discharged via P1, R2 and D6. When the potential across C2 drops, the brightness of the LED diminishes, so that the p.d. across R3 also drops. The increasing resistance of R3 effects phase angle control of the triac so that the light is dimmed gradually. The dimming time may be altered with P1 within the time range determined by network R2-C2. The circuit operates correctly only, of course, when the LDR is not exposed to light other than that from the LED. The type of LDR is not particularly important, as long as it is not too long: in the prototype, a model with a length of 5 mm was used.

 Author:Schallmoser

Source - http://www.extremecircuits.net/2010/07/automatic-light-dimmer.html

C - Elektor Electronics

13:16 0 comments

LED Traffic Lights

Description 

 The LED traffic Light circuit controls 6 LEDs (red, yellow and green) for both north/south directions and east/west directions. The timing sequence is generated using a CMOS 4017 decade counter and a 555 timer. Counter outputs 1 through 4 are wire ORed using 4 diodes so that the (Red - North/South) and (Green - East/West) LEDs will be on during the first four counts. The fifth count (pin 10) illuminates (Yellow - East/West) and (Red - North/South). Counts 6 through 9 are also wire ORed using diodes to control (Red - East/West) and (Green - North/South). Count 10 (pin 11) controls (Red - East/West) and (Yellow - North/South). The time period for the red and green lamps will be 4 times longer than for the yellow and the complete cycle time can be adjusted with the 47K resistor. The eight 1N914 diodes could be subsituted with a dual 4 input OR gate (CD4072). 

Circuit diagram

Source http://www.bowdenshobbycircuits.info/page10.htm#traffic.gif

11:02 0 comments

Running Message Display LED Circuit

Description

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 CD4017BE’s 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. On reset, output pin 3 goes high and drives transistor T7 to ‘on’ state. The output of transistor T7 is connected to letter ‘W’ of the LED word array (all LEDs of letter array are connected in parallel) and thus letter ‘W’ is illuminated. On arrival of first clock pulse, pin 3 goes low and pin 2 goes high. Transistor T6 conducts and letter ‘E’ lights up. The preceding letter ‘W’ also remains lighted because of forward biasing of transistor T7 via diode D21. In a similar fashion, on the arrival of each successive pulse, the other letters of the display are also illuminated and finally the complete word becomes visible. On the following clock pulse, pin 6 goes to logic 1 and resets the circuit, and the sequence repeats itself. The frequency of sequencing operations is controlled with the help of potmeter VR1.

Circut Diagram:

The display can be fixed on a veroboard of suitable size and connected to ground of a common supply (of 6V to 9V) while the anodes of LEDs are to be connected to emitters of transistors T1 through T7 as shown in the circuit. The above circuit is very versatile and can be wired with a large number of LEDs to make an LED fashion jewellery of any design. With two circuits connected in a similar fashion, multiplexing of LEDs can be done to give a moving display effect

 Source http://www.electronic-circuits-diagrams.com/lightsimages/lightsckt5.shtml

10:33 1 comments

AC 220 Volts Flashing Lamps Circuit

Circuit diagram 

This circuit is intended as a reliable replacement to thermally-activated switches used for Christmas tree lamp-flashing. The device formed by Q1, Q2 and related resistors triggers the SCR. Timing is provided by R1, R2 & C1. To change flashing frequency do not modify R1 and R2 values: set C1 value from 100 to 2200µF instead.

Best performances are obtained with C1= 470 or 1000µF and R4= 12K or 10K. Due to low consumption of normal 10 or 20 lamp series-loops intended for Christmas trees (60mA @ 230V typical for a 20 lamp series-loop), very small and cheap SCR devices can be used, e.g. C106D1 (400V 3.2A) or TICP106D (400V 2A), this last and the suggested P0102D devices having TO92 cases.

Parts: 

• R1 = 100K
• R2 = 1K
• R3 = 470R
• R4 = 12K
• R5 = 1K
• R6 = 470R
• Q1 = BC327
• Q2 = BC337
• D1 = 1N4007
• D2 = 1N4007
• D3 = 1N4007
• D4 = 1N4007
• D5 = P0102D (SCR)
• C1 = 1KµF-25V
• PL1 = Male Mains plug
• SK1 = Female Mains socket

Important Note:

For proper operation it is absolutely necessary to employ high Gate-sensitive SCRs. If you are unable to find these devices you can use Triacs instead. In this case the circuit operates also with relatively powerful devices. A recommended Triac type is the ubiquitous TIC206M (600V 4A) but many others can work. Please note that, in spite of the Triac, diode bridge D1-D4 is in any case necessary.

Warning! The device is connected to 230Vac mains, then some parts in the circuit board are subjected to lethal potential! Avoid touching the circuit when plugged and enclose it in a plastic box.

Source  http://www.extremecircuits.net/2009/08/ac-220-volts-flashing-lamps-circuit.html

10:13 0 comments

Dark Activated Led or Lamp Flasher

Description 

This circuit adopts the rather unusual Bowes/White emitter coupled multivibrator circuit. The oscillation frequency is about 1Hz and is set by C1 value. The LED starts flashing when the photo resistor is scarcely illuminated. The onset of flashing can be set by trimming R2. 

Circuit Diagram:

Parts:

• R1 = LDR
• R2 = 100K
• R3 = 10K
• R5 = 470R
• R6 = 47R
• R4 = 10K
• C1 = 220uF-25V
• D1 = 1N4148
• D2 = LED any type (see notes)
• Q1 = BC337
• Q2 = BC337
• B1 = 3V Battery or 2x1.5V cells in series
• SW1 = SPST Switch

Notes:

• Best results in flashing frequency can be obtained using for C1 a value in the 100 - 1000µF ranges.
• To drive a filament lamp make the following changes:
• Use a 2.2 to 3V, 250-300mA bulb in place of the LED
• R2 = 10K 1/2W Trimmer Cermet
• R3, R4 = 1K 1/4W Resistors
• R6 = 1R 1/4W Resistor
• C1 = 470 to 1000µF 25V Electrolytic Capacitor
• In LED-mode operation the stand-by current consumption is less than 400µA.
• In Lamp-mode operation the stand-by current consumption is about 3mA. 

 Source  http://www.extremecircuits.net/2009/07/dark-activated-led-or-lamp-flasher.html

10:07 0 comments

Photocell based night light

Description.

Many automatic night light circuits had been published here. This one uses a photocell for detecting the light intensity. At full light the resistance of the photocell will be few ten ohms and at darkness it will rise to several hundred ohms. The IC1 uA741 is wired as a comparator here. At darkness the resistance of photocell increases and so the voltage at the inverting input of the IC1 will be less than the reference voltage at the non inverting input. The output of the IC1 goes to positive saturation and it switches ON the transistor to activate the relay. By this way the lamp connected through the relay contact glows. The diode D1 works as a freewheeling diode.

Circuit diagram.

Notes.

• The circuit can be assembled on a Vero board.
• Use 9V DC for powering the circuit.
• POT R7 can be used to adjust the sensitivity of the circuit.
• The relay K1 can be a 9V, 200 Ohm SPDT type.
• L1 can be a 230V,60W lamp.
• R8 can be a ORP 12 photocell.

09:22 0 comments