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I'm currently working on designing an incandescent traffic light system and could use some guidance on extending and optimizing my design. Initially, I've successfully implemented the required specifications for a single lamp. Now, I'm looking to scale up the design to accommodate three traffic lamps in a cost-effective and efficient manner.

Current Progress:

For a single lamp, I've developed the following block diagram and corresponding schematic. Simulation results indicate satisfactory functionality. Here are the details:

[Insert Picture of Block Diagram] [Insert Picture of Schematic]

Expansion Plan:

My plan is to extend this design to incorporate three lamps, preferably in a parallel configuration. However, I have concerns about potential synchronization issues with the 555 timers, leading to simultaneous illumination of multiple lamps.

Key Components:

The timing of the lamps is controlled by 555 timers, as illustrated in the attached figure. Additionally, a daylight detector is employed to switch between two brightness levels, facilitated by a relay/SPDT setup. enter image description here

Seeking Advice:

Optimization Tips: I would appreciate any suggestions on optimizing the design for three lamps while maintaining efficiency and cost-effectiveness.

Synchronization Concerns: How can I ensure that the 555 timers remain synchronized to prevent overlapping lamp activation? Additionally I want each 555 timer to switch on the mains for its corresponding lamp via a relay.

Safety Considerations: As I haven't conducted physical testing yet, are there any potential safety hazards I should be aware of with this circuitry?

I'm open to any insights, tips, or recommendations that could help improve and refine my design. Thank you in advance for your assistance!

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  • \$\begingroup\$ Why use 555 timers? Is that part of the design requirements? \$\endgroup\$ Commented Mar 28, 2024 at 16:26
  • \$\begingroup\$ Yes. It's a fundamental analogue design project. So no microcontrollers. Just the basics of analogue design from first principles \$\endgroup\$ Commented Mar 28, 2024 at 16:29
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    \$\begingroup\$ Does "fundamental analog design" include logic gates? Better share all the constraints and requirements (edit them into your question) so we're not playing 20 questions here. \$\endgroup\$ Commented Mar 28, 2024 at 16:35
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    \$\begingroup\$ You should use a single master clock so you don't have synchronization problems. Use counters based on the master clock and logic circuits to derive the switching times for the various lights. \$\endgroup\$ Commented Mar 28, 2024 at 17:24
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    \$\begingroup\$ yep, this is actually a discrete-time discrete-state space control problem! Discrete in time, and discrete in states, that's actually the definition of the word "digital"; so, using an approach that tries to ignore the "digitality" of your problem is not going to work out great: Even in times before digital ICs, traffic lights were controlled by literal clocks ticking time away, causing discrete events. So, I'd strongly recommend you go Peter Bennett's route. As a project to learn analog circuitry, it's a relatively ill-suited problem statement: nothing a traffic light does is analog. \$\endgroup\$ Commented Mar 28, 2024 at 17:27

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Given these unusual constraints, this is how I would do it (not really. I'd use a micro, or PLC):

schematic

simulate this circuit – Schematic created using CircuitLab

You have 6 lights that you need to control, but only 4 states. A simplification to the logic is the opposite RED light is always on when either the GREEN or YELLOW light is on.

The 555 timer is set to put out a pulse every 5 seconds. The reason for 5 seconds is that 5 is the common denominator of all the durations: 45s, 40s, 15s, and 5s. This timer clocks the 4017 decade counters at this rate. After a green then yellow sequence is up, the counter locks it self out of incrementing. At the same time it locks it self out, it resets the other counter. The 3 NOT gates and an AND gate generate the reset pulse. This is needed to prevent a deadlock condition in which both counters can latch into reset forever. The same situation happens in complementary fashion with the other counter. The sequence will repeat indefinitely. Using diode logic, the RED lights are OR'ed with the opposing GREEN and YELLOW lights.

The brightness controller shorts out the dimmer when in daylight. I'm not designing that here; there are hundreds of circuits you can stick in the box to control a relay via light sensors.

This is really the nuts and bolts of it. There are plenty of improvements and otheer considerations, but this seems like a pretty good start.

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