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Pedestrian Crossing Light Project

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tobias1997

New Member
I am attempting to design and implement a digital circuit for pedestrian traffic light in a way when a push button is pressed a red light become on and stays on for 10s showing the activation of the 'traffic light'. Then a green light becomes on and stays on for 5s which shows the pedestrian can pass the street. After that the light becomes off.

I am using a 555 timer ic to control the time the LED's are illuminated for, ( i have sorted the timings) and have been given a NAND ic chip to switch between the two timers so that the green activates after the red. I am relatively new to electronics so do not know how to achieve this, i understand that you can use a NAND chip to create other logic gates but do not know which to create to achieve the results.
This project is being attempted on a breadboard, any help would be greatly appreciated!
Thanks!
 

Flyback

Well-Known Member
i think you need karnaugh maps and state tables, then you can do it using de morgans laws and nand gates...or else, take the easy way out and use a microcontroller and assembler or c..perhaps arduino or pic
 

absf

Active Member
I am using a 555 timer ic to control the time the LED's are illuminated for, ( i have sorted the timings) and have been given a NAND ic chip to switch between the two timers so that the green activates after the red. I am relatively new to electronics so do not know how to achieve this, i understand that you can use a NAND chip to create other logic gates but do not know which to create to achieve the results.
This project is being attempted on a breadboard, any help would be greatly appreciated!
Thanks!
Are you saying that you may use 2 x 555 for the 10S and 5S timing, plus another 4011 NAND gate to manage the 2 timers one after another lighting one red and one green LED?

It sounds like homework to me.:rolleyes:

Allen
 
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AnalogKid

Well-Known Member
Most Helpful Member
If the pattern is this:
All off
Push button
Red on for 10 s.
Green on for 5 S.
All off

Then I don't think you need the NAND gate. Look on the 555 datasheet for the Monostable circuit. The switch and 1 resistor trigger the first 555 set for 10 s through the Trigger input; the output drives the red LED. That output also is connected to the second 555, set for 5 s through a capacitor to its Trigger input and a resistor to Vcc. It drives the green LED.

ak
 

MikeMl

Well-Known Member
Most Helpful Member
If the pattern is this:
All off
Push button
Red on for 10 s.
Green on for 5 S.
All off

Then I don't think you need the NAND gate. ..
Now, suppose that the teacher is only slightly more experienced than the student, and THINKS it cannot be done without some NAND gates...

All off
Push button
Button triggers both timers X and Y at the same time, X is set to be high for 10s, Y is set to be high for 15s
Red LED is on while X and Y are both high simultaneously (for the first 10s)
Green LED is on while X is low and Y is high (for the last 5s)
No LEDs on if X and Y are both low.
 

MikeMl

Well-Known Member
Most Helpful Member
Can anybody do it with less components than this? Plot the current through D1 and D2.
 

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absf

Active Member
That was ingenious. ;):D

After the button is pressed. Both X and Y go high from 2s to 12s so only D1 is ON.
After X goes low at 12s and Y remains high, D2 is ON until 17S and D1 is off.

Saves an 4011 NAND.

PedX Sim.PNG

Allen
 

MikeMl

Well-Known Member
Most Helpful Member
That was ingenious. ;):D...
Did you like what I called the signal that pushes the button?

D2 is driven by an "h-bridge" :)
 
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