T-Junction traffic lights project HELP!

[sharan89.k]

hi, i need to design a t-junction traffic light system using only digital logic design. here is my circuit. but when i simulated, it stays just in the state as in the picture, which is green, red, red. it is not changing to the next sequence. any help with the circuit is much appreciated!

 

[ericgibbs]

hi,
There a number of problems.
Say when U2 pin 3 is high, Q1 is switched ON, the Gn LED in the emtter has no series current limit resistor so the emitter of Q1 is at about 2V , drawing a high current.
This means also that base voltage of Q1 is held at ~+2.7V,,, so the U3A input will not be high enough to be seen as logic high.

The same points apply to the remainder of the transistors.

 

[sharan89.k]

hi,
There a number of problems.
Say when U2 pin 3 is high, Q1 is switched ON, the Gn LED in the emtter has no series current limit resistor so the emitter of Q1 is at about 2V , drawing a high current.
This means also that base voltage of Q1 is held at ~+2.7V,,, so the U3A input will not be high enough to be seen as logic high.

The same points apply to the remainder of the transistors.

thanks! that really helped me a lot to understand how the circuit works and resolve the problem! here is the slightly modified circuit which works just fine. THANKS AGAIN!

 

[ericgibbs]

hi,
Well done.!
Thanks for the feedback.

 

[ljcox]

You have taken this circuit from another thread.

I did not bother to point out to the other OP that the transistors are not necessary.

The LEDs can be driven directly from the 4017 via the diodes.

I would include a diode on those that don't strictly need one in order to prevent the possibility of excessive reverse voltage being applied to the LEDs when they are off.

 

[sharan89.k]

You have taken this circuit from another thread.

I did not bother to point out to the other OP that the transistors are not necessary.

The LEDs can be driven directly from the 4017 via the diodes.

I would include a diode on those that don't strictly need one in order to prevent the possibility of excessive reverse voltage being applied to the LEDs when they are off.

hi! yes i've taken it from the other thread but found some small problems with it, such as the blinking and transition of the lights are not smooth and etc. so, modified the circuit and resolved the problems. and yea i was wondering about the importance of transistors in this circuit but never bothered to remove them and test, which i will do it later. but, what is the good side/bad side of having transistors in this circuit?

thanks for helping!

 

[ljcox]

The other OP never told us how it went.

The transistors are only necessary if you want to have a high LED current.

If that was the case, then you would need transistors for the Red LEDs also.

So if the LEDs are bright enough without the transistors & the LED current is not loading the 4017 too much, then you don't need the transistors.

You're welcome.

 

[ljcox]

If you remove the transistors, then I suggest that you make resistors R6 ~ R11 = 1k like the others.

EDIT

PS. I told the other OP that he needed resistors in series with the LEDs. See the amended circuit I posted on his thread.

However, I confused myself at one point & told him that the resistors & LEDs should be connected to +9 Volt, not 0 Volt.

 

[sharan89.k]

The other OP never told us how it went.

The transistors are only necessary if you want to have a high LED current.

If that was the case, then you would need transistors for the Red LEDs also.

So if the LEDs are bright enough without the transistors & the LED current is not loading the 4017 too much, then you don't need the transistors.

You're welcome.

i see. my circuit is still in the simulation level and I still haven't really finished connecting my hardware yet. will try out the hardware with the mods that you suggested and will update as soon as im done.

 

[sharan89.k]

If you remove the transistors, then I suggest that you make resistors R6 ~ R11 = 1k like the others.

EDIT

PS. I told the other OP that he needed resistors in series with the LEDs. See the amended circuit I posted on his thread.

However, I confused myself at one point & told him that the resistors & LEDs should be connected to +9 Volt, not 0 Volt.

hi, im done connecting the hardware and without the transistors. it did not work out well, which i dont know why. lol. stayed with the old design with transistors for the green and yellow LEDs, and without one for the reds. connected 680Ω and 1kΩ in series with the LEDs and everything is working fine now. here is the schematic of the completed project again.

Would like to say THANKS again to you guys! appreciate it!

and

MERRY CHRISTMAS!

 

[ljcox]

LEDs 3, 6 & 7 don't have transistors, so the others should not need them either.

Glad to be able to help.

Merry Xmas to you also.

EDIT
I just checked the source current capability of the 4001 versus the 4017.

The 4001 has more than twice the souce current capability. So you could try a lower resistor for the LEDs connected to the 4017 - given that it is only driving the LEDs

 

[GTCT]

Electronic traffic light at t junction

Electronic traffic light at t junction

 

[4pyros]

Electronic traffic light at t junction

What the...........................