Electronics > Beginners
Traffic light circuit with 556 timer?
schmitt trigger:
The exact same diagram, with a single 556?
Short answer; No. For the reason I provided in post #4.
Perhaps instead of powering the second timer, you could manipulate the reset. Which the 556 will have two independent resets.
SmokeyTheElectrician:
--- Quote from: phennessey on December 20, 2019, 08:52:52 pm ---Disclaimer: this is my first electronics project ever. I understand basic electronic components and how they work, but I've never built anything in my life. I thought this project was a good starting point.
I want to build the following "traffic light" circuit that uses two 555 timers to light up three LEDs in sequence:
(Attachment Link)
But...I want to use a dual 556 timer instead of two 555 timers. I attempted to re-draw this circuit with the correct pinouts and removed the extra in/out lines. I don't think I did it right...can anyone help me redraw this so that it would work with a single 556 IC?
Some info on the pinouts for the 555 and 556:
https://dlb.sa.edu.au/rehsmoodle/file.php/466/kpsec.freeuk.com/555timer.htm
Also, would it be a bad idea to build this thing on a mini 170-pin breadboard with no power rails? Is there enough room on one of those to build this?
Thanks for any help you can provide!
--- End quote ---
You are actually very close to having that circuit right.
For the 555 on the right side, you must have gotten
scrambled up 'cause:
a) the Orange LED circuit high side should come from the left side 555's output ( not 12 volts)
b) pin 8 for the right side 555 should go to 12 volts ( not the left side 555's output )
c) pin 4 for the right side 555 should go to the left side 555's output ( not 12 volts )
I think that should do it.
Let us know how it works out for you,
or if you could use more help.
( post circuits, drawings, wave forms, both from simulation and IRL )
BTW if the right side circuit was in the configuration where you could set the duty cycle,
you would be able to get the periods of the red cycle and green cycle to match almost
exactly -- refer to figure 14 on page 10 in TI's 555 Datasheet - https://www.ti.com/lit/ds/symlink/lm555.pdf.
good luck
and
cheers to all
SmokeyTheElectrician:
--- Quote from: schmitt trigger on December 21, 2019, 12:50:37 am ---I can see where his confusion is.
The left 555 powers up via its output (pin 3) the right 555's Vcc input (pin 8 ).
This circuit cannot be implemented with a 556, which share a common Vcc input.
But even then, the circuit's operation is suspect. How does the circuit cycle back to the red light once that the green times out? There is no signal feedback from right to left.
--- End quote ---
The timer on the left just free runs.
The timer on the right has a period long enough that it does not quite fit in a half cycle of the first.
I do not know the OP's source for the circuit, but after realizing the above, it seemed the idea
was to hold the right side timer in reset for half of a cycle of the left side timer and then let
it run during the left side timer's other phase (output high). I think if the right hand circuit
would have been a one shot, the design would have been easier to decipher...
Cheers to all
ebastler:
--- Quote from: phennessey on December 22, 2019, 01:53:34 am ---My goal is to use as few components as possible!
--- End quote ---
That would be a small microcontroller. 8-pin DIP, 6 I/O pins -- just enough for the lights at both crossroads. You need just the single chip, plus LEDs and series resistors. (If you use a star network, that's just one package for the resistors too.) And you can implement any signal sequence and timing you like.
I realize that you may want to do this with 555s as an intellectual exercise. But a microcontroller is really the way to go for a practical implementation.
phennessey:
No, not the same diagram. I mean the same components. Can these components produce the effect?
556 timer
2x 100uF caps
5x resistors with the values listed
3 LEDs blinking in sequence (Gr long, Yl. short, Rd. long)
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