Traffic Light Project

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This project operates red, amber and green LEDs in the correct sequence for a single UK traffic light. The time taken for the complete red - red & amber - green - amber sequence can be varied from about 7s to about 2½ minutes by adjusting the 1M preset. Some amber LEDs emit light that is almost red so you may prefer to use a yellow LED.

The 555 astable circuit provides clock pulses for the 4017 counter which has ten outputs (Q0 to Q9). Each output becomes high in turn as the clock pulses are received. Appropriate outputs are combined with diodes to supply the amber and green LEDs. The red LED is connected to the ÷10 output which is high for the first 5 counts (Q0-Q4 high), this saves using 5 diodes for red and simplifies the circuit. 

This project uses a 555 astable circuit to provide the clock pulses for the 4017 counter.

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Parts Required

• resistors: 470 ×3, 22k, 100k
• capacitors: 0.1µF, 1µF 16V radial, 10µF 16V radial
• diodes: 1N4148 ×6
• LEDs: red, amber (or yellow), green
• 1M preset, horizontal
• 555 timer IC, such as NE555
• 4017 counter IC
• DIL sockets for ICs: 8-pin, 16-pin
• on/off switch
• battery clip for 9V PP3
• stripboard: 20 rows × 21 holes

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Stripboard Layout

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Circuit diagram

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A kit for this project is available from RSH Electronics. If you are new to electronics buying a kit is a good way to be sure you have the correct parts for the project. 

LED strobe has independent delay and duration

LED circuit diagram - LED strobe has independent delay and duration
	The circuit applies a 5V pulse, the main clock, to diode D1and capacitor C1 to form a peak-hold circuit. C1 then discharges at a rate that P1 sets. Michael C Page, Chelmsford, MA, USA
High-brightness LEDs, with independent delay and duration, find use in a visual-inspection application. The circuit is not complex, but it saved the day in an application involving visual inspection of the spray pattern of fuel injectors for quality and consistency.

Switch Circuit Diagram - Dark-activated switch needs only three components
	When you light the photocell, its voltage drop is lower than the triggering level of the threshold voltage, and Q1 is locked By Abel Raynus, Armitron International, Malden, MA, USA
Assume that you have a device that receives its power from the main 120 or 220V-ac line and you need to add a switch between the ac line and the device so that the device works only when it is dark. Although you may think this task would be trivial, it is difficult to find a workable approach.

The circuit is based on a voltage comparator circuit wired around IC 1.The non inverting in put of IC1 is given with a reference voltage of 6V using resistors R3 and R4. The input to the inverting input will be the voltage across the LDR that is light dependent.At darkness the resistance of the LDR will be high and so do the voltage across it.At this condition the voltage at the inverting input will be higher than the reference at non inverting pin and the out put of the comparator will be low(~o V).When the LDR is illuminated ,its resistance drops and so do the voltage across it.Now the voltage at inverting input will be lower than that at non inverting input and the out put of the comparator goes high (~12 V).This makes transistor Q1 on and it drives the relay.As a result we get a relay switching according to the intensity of the light falling on the LDR.

Notes.

• Adjust POT R1 to set the desired light intensity for switching the relay.For this illuminate the LDR with the desire intensity light.The relay will be either on or off.Adjust POT R1 slowly so that the state of the relay changes.That’s it.Now the circuit is set for the given intensity of light.
• Assemble the circuit on a good quality PCB or common board.
• You can use either a 12 V battery or a well regulated & filtered 12V DC mains operated power supply.
• The pin 5&6 (Balance & Balance/Strobe ) of IC LM311 are shorted to minimize the chance of oscillations.
• The pin out of LM311 is also given together with the circuit diagram.

Read more: http://www.circuitstoday.com/light-activated-switch-circuit#ixzz0wNLSEteg
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