The Request
Hi Mr Majumdar,
I recently came upon your website while researching circuits for a hobby project i'm working on. I certainly admire your work.
I was hoping you might be able to put together a simple circuit for an illuminated pedestrian crosswalk system I want to build and install in the car park of my building. There is heavy traffic and crossing the road at night can be dangerous.
I want to build a lighting system that is push-button activated like a typical pedestrian crossing, but with alternate strobing LED arrays and, most importantly, simultaneously active an array of high-power white LEDS to actually illuminate the crosswalk. It would be great if the whole thing could be powered by solar so that it could be self-contained and not rely on getting mains power.
Thanks so much in advance!
Best regards,
George
The Design
The requested Illuminated crosswalk safety light circuit can be easily built using a few 555 ICs, and some passive electronic components as shown below:
Referring to the figure above, the left side IC 555 is configured as a bistable for enabling the required push-button operated ON/OFF actions. The "SET" button initiates the IC 555 and causes a high logic to appear at its pin#3, while the "RESET" button deactivates the IC operation and switches OFF pin#3 logic to a zero.
In the activated mode the bistable stage powers the right side IC 555 stage which is wired as a standard astable circuit for generating a flashing or blinking output at its pin#3 which in turn causes the attached red LEDs to light up with a rapid flashing effect, simulating a strobing light.
The strobing rate can be controlled through the 100k pot associated with the astable IC 555 stage.
Along with the activation of the the strobing lights, the bistable stage also triggers and illuminates a power LED via a driver transistor TIP122, so that the crosswalk could be illuminated with sufficient light for the user.
Once the user has crossed the path, pressing the RESET button toggles off the whole system until the SET button is pressed yet again by some other pedestrian.
In order to make the system self contained, this illuminated crosswalk safety circuit employs an appropriately rated solar panel and a compatible 12V rechargeable battery for powering the circuit and the LeDs.
During day time the battery is charged, and when darkness sets in, the battery reverts its power for the intended crosswalk safety light operations.
The battery and the panel specifications will depend on the type of LEDs used for the purpose.
The emitter-follower transistor configuration attached with the solar panel ensures a controlled charging for the battery and never allows it charge over a predetermined level, as set by its base zener diode.
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