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[SOLVED] Traffic Light Timer using 74192 and 555 timer

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Newbie level 4
Jun 14, 2015
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Traffic Light Timer must countdown 30sec green 10sec yellow 15sec red

I already accomplished the timer with an astable multivibrator

Now, I am stuck with the timer.. can anyone help me thanks


Hi there!
Sorry, I don't understand - What do you mean you are stuck with the timer? - A circuit without a 555 in it is probably lacking something, there's always an excuse to use one!

But seriously, this schematic by this guy might help, I've used (or slightly adapted where necessary) quite a few of his 555 circuits and they have all worked so far: "Three Stage - Cycling Timer Circuit" **broken link removed**

If not, there are also these:

By the way, if you are fussy about precision timing, the LMC555 is a nice choice for a few pennies more than an NE/SE or LM, it can only drive up to 100mA, but it can achieve 1.25mS consistent timing accuracy according to the datasheet.

The Rob Paisley stuff is usually spot-on. If it's a different sort of problem related to the timer, please explain a little more and I may be able to help.


Im trying to make the 74LS192 countdown on a specific time sequences (30, 10 and 15). Im stuck there and what im trying to do is to implement the parallel loads and im confused about it.. sorry for not stating it earlier
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Hi frito23,
Okay, I'm having difficulty seeing the details of the pin uses in the schematic, when I enlarge it gets blurry - sorry. If you haven't quite resolved this yet, if you don't mind could you maybe re-post the schematic larger/as a jpg, please, and I'll be happy to scratch my head for a while, not promising anything but I'll gladly give it some thought if you want.

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Hi again,
To be honest I'm not familiar with this BCD counter or the 7-segment BCD decoder,(I know the 4026/4033, 4511, 3161 and another I can't remember now), but I have been looking at the datasheets for both your ICs, and at other 74192/7447 circuits (for what that's worth), and something I don't know about the 74192 so I wonder: Are you trying to get three different timed pulse signals from 1 astable 555? If so, can your circuit/47192s create the 3 distinct time sequences from 1 astable 555 pulse?
I ask because I've been working (off and on) on a circuit that uses 4017s and 555s to control 3 motors, and it would only work with a monostable - possibly two - for the timing I need (30 seconds total, 21 seconds for one sequence and 9 seconds for the second) controlling three different astable 555s which drive the various 4017 cyclical counts. Besides that, for something else I needed to use 3 timers to do a set/reset function for a hands-free stopwatch circuit, it wasn't possible with less.
At first glance it looks like that circuit works with a switching input signal, or one per traffic light sequence.
Perhaps for what you are doing a PIC would be nice for the more complex functionality you may need, and to use far less parts, but I drag my feet in that regard as 6 months to learn how to configure and code the things just to finish a circuit you are already halfway through is maybe not worth it.
As I'm not much use to solving your puzzle I suspect, I hope maybe these links can help you:

Controlling Circuits For LM555 Timers:
**broken link removed**

I'm happy to help if I can, feel free to ask if I can actually help, but not happy to waste your time with bad/useless advice, my friend, that would be unfair to you. Best of luck.

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And hi yet again...

Just remembered, last thing is: Have you tried doing a truth table for your circuit, or even just a block diagram of "in" and out" signal paths, and looking at it from the point of view of whether it is combinational logic, sequential logic or a mixture both? (Quite a few "simple" circuits are a bit of both). Both plans of attack usually help a lot to see what's happening/what should be happening, and what may or may not be missing for that result to happen. I do this when a circuit is getting the better of me (which happens quite often!), it helps to see the wood from the trees, and to remember the mechanics of a circuit apart from the distraction of incorrectly flashing LEDs!
Maybe you just need a standard logic IC of some sort (NOT/AND/OR/NAND/XOR/whatever...) to complete your circuit function instead of multiple 555s. For example, you know how 24-hour clocks use a dual or quadruple input AND gate to get 59 (60) seconds to reset, likewise with 59 (60) minutes and 24 hours by using the a to g outputs to feed the 4 AND inputs which makes the AND output reset the necessary counters and clock +1 on the next counter.
Once again, best of luck!
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