Pedestrian Crossing Light Project

[tobias1997]

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!

 

[Harald Kapp]

I don't think you need the NAND at all.
The first 555 is triggered by the negative edge from the push button (the standard application as a monostable multivibrator). While ctive it lights the red LED.
The output from the first 555 triggers the second 555. As the 2nd 555 is negative edge triggered, it will be trigered when the 1st 555 turns off. The output of the 2nd 555 turns on the green LED.

 

[tobias1997]

i have the red LED connected to pin 3 of the first 555 and have now also connected pin 3 of the first 555 to pin 2 of the second 555. Both 555 timers are setup as mono-stable multi-vibrators. however when connected to the battery the green LED is default on, when the button is pressed the red turns on for 10s and green off, then green goes back to default on and remains on, ignoring the timings altogether

 

[Harald Kapp]

Show us a complete circuit diagram. Judging a circuit from a verbal description is hard to impossible.
DO you have the 555's trigger inputs decoupled by a high pass filter (capacitor) as shown here?

 

[Arouse1973]

Just found this simulator it may help you. Looks quite impressive. It's free for a few days and then you go on to the hobbyist version.
http://www.docircuits.com/search-circuits/tags/MULTIVIBRATOR
Thanks
Adam

 

[Harald Kapp]

I had some leisure time...

This circuit is made of tw 555 timer ICs, both set up as monostable multivibrators.
V1 is a power supply at 12 V - any voltage within the operating range of a 555 will work.
V2 is a voltage source which creates a low going pulse to start the timers. This is a jury rig for a pushbutton conecting the input to ground (0V) in a real circuit.
The output (3) of each 555 drives a buffer transistor (any NPN with suitable collector current rating will work) which in turn delivers the current for the LED. The curent through the LED is limited by a series resistor.

The simulation shows this result:

The green line is V2. You can see it is mostly at 12 V, only a short pulse at the beginning goes down to 0V. This would be the push of the button (In reality, a button will need another resistor e.g. 1kΩ from the left side of the input capacitor to 12 V. This is not shown here).
The blue line is the current through LED D1 (red) showing it to be on for 11s (t=1.1*R*C). When the leftmost 555 turns off, LED D1 is turned off, too, and the right 555 is triggered. In turn the current through LED D2 (LED color green, signal color red) is turned on.

I think this circuit pretty much is what you need. component values may be tweaked to better match your timing requirements.

 

[tobias1997]

This is the circuit i have built so far. For the project i have to use a nand gate to detect / change the lights. As it is currently the green is on as soon as the battery is connected.
So i need to use the Nand gate to trigger the the second timer once the first has been on then turned off.
and the Green led to be off by default.
Thanks for the help!