Traffic light circuit with 556 timer? - Page 1
Forum section: electronics / beginners

author: phennessey
author_rank: Contributor
timestamp: December 20, 2019, 08:52:52 pm
content: 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: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.htmAlso, 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!

author: Wimberleytech
author_rank: Super Contributor
timestamp: December 20, 2019, 10:57:59 pm
content: Quote from: phennessey on December 20, 2019, 08:52:52 pmIt would be instructive for you to try to figure this out on your own. It is easy to map the functions of the pins to their respective pins.You need to put a bypass capacitor across the supply pins (not shown in your schematic). Post your result and I or someone else will check your work.There may be enough room to build it but you need to try to figure that out. Download a copy of Fritzing and build it there first. You can optimize placement and know ahead of time if there is enough room.

author: james_s
author_rank: Super Contributor
timestamp: December 21, 2019, 12:19:39 am
content: The 556 has exactly the same pins as a pair of 555s except there is only one set of power and ground pins. What aspect is confusing you? Draw it up to the best of your ability and share that drawing and we can help you figure out anywhere you went wrong.

author: schmitt trigger
author_rank: Super Contributor
timestamp: December 21, 2019, 12:50:37 am
content: 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.

author: phennessey
author_rank: Contributor
timestamp: December 21, 2019, 01:32:10 am
content: Thank you! I thought I was taking crazy pills.Is there a way to wire three LEDs to a single 556 that would produce the same effect?

author: Wimberleytech
author_rank: Super Contributor
timestamp: December 21, 2019, 02:32:53 am
content: Quote from: schmitt trigger on December 21, 2019, 12:50:37 amDerp...good catch. I did not notice that!

author: schmitt trigger
author_rank: Super Contributor
timestamp: December 21, 2019, 06:15:45 pm
content: Traffic lights are classic classroom example when learning about state diagrams and/or truth tables.I have made a fictional intersection in a pair of streets: Second avenue and Main street. Please check the attached Excel spreadsheet.To keep things simple, I've arbitrarily made them one way, and have not included turn signals.The circuit has four states, which repeat endlessly and six outputs, one each for each light color on a street.Fortunately, four states can be realized with a two bit counter, with a single IC dual flip flop like the CD4013.Then using sums of minterms, you decode each output. For instance, the Second ave green light is simply A * B/The fact that the yellow light has a different duration than the other lights complicates things a little, but with additional steering logic you could change your astable's time constant.Of course, doing this with a microcontroller is trivial.

author: james_s
author_rank: Super Contributor
timestamp: December 21, 2019, 06:27:10 pm
content: Wow I didn't even notice the second IC was powered by the first, that's quite a strange way of implementing a traffic light.

author: rstofer
author_rank: Super Contributor
timestamp: December 21, 2019, 06:52:52 pm
content: Quote from: schmitt trigger on December 21, 2019, 06:15:45 pmIn the US, the 'warn' signal is never given.

author: james_s
author_rank: Super Contributor
timestamp: December 21, 2019, 07:17:13 pm
content: As one of the small minority of people who still insists on a proper manual gearbox I've often wished it was. Seems like a handy feature that has never been implemented in this part of the world.

author: rstofer
author_rank: Super Contributor
timestamp: December 21, 2019, 08:06:10 pm
content: Quote from: james_s on December 21, 2019, 07:17:13 pmWell, in the '60s, we would have used it to put torque on the rear wheels in anticipation of getting the green light. Street racing...I first encountered it when I was stationed in Germany. I thought it was a very efficient way to tell people it was just about time to go. I wonder how many T-bone accidents it facilitates.

author: james_s
author_rank: Super Contributor
timestamp: December 21, 2019, 08:10:55 pm
content: I haven't ever bothered to look at any statistics on that. I've formed a habit of looking at the cross street signals if I can see them and when those turn yellow I put my car in gear. I like having a warning so I'm not either holding the clutch down the whole time I'm sitting there, or abusing the 1st gear synchro by stuffing it into gear to go before the guy behind me has a fit.

author: Zero999
author_rank: Super Contributor
timestamp: December 21, 2019, 09:54:31 pm
content: The sequence seems to differ the world over.In the UK it's:RedRed&AmberGreenAmberRedWhat sequence does the original poster require?If it's just sequentially lighting the LEDs one after the other, just use a ring oscillator. Here's an example which can be built with the 74HC14.

author: schmitt trigger
author_rank: Super Contributor
timestamp: December 22, 2019, 01:50:59 am
content: Quote from: Zero999 on December 21, 2019, 09:54:31 pmExactly,That is the reason I suggested to the OP that he must construct a truth table listing all the states on all the roads.But perhaps he only requires to build a ring oscillator, just like you indicated.

author: phennessey
author_rank: Contributor
timestamp: December 22, 2019, 01:53:34 am
content: Red, green, yellow. That simple. Timing: Red and green for longer, yellow shorter.I’m trying to use only a 556 timer and the components listed in the diagram. Can it be done? I already ordered these components from Digikey...honestly just hoping there’s a way to do it with them. My goal is to use as few components as possible!

author: schmitt trigger
author_rank: Super Contributor
timestamp: December 22, 2019, 05:14:31 am
content: 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.

author: SmokeyTheElectrician
author_rank: Contributor
timestamp: December 22, 2019, 02:14:42 pm
content: Quote from: phennessey on December 20, 2019, 08:52:52 pmYou are actually very close to having that circuit right.For the 555 on the right side, you must have gottenscrambled 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 almostexactly -- refer to figure 14 on page 10 in TI's 555 Datasheet -https://www.ti.com/lit/ds/symlink/lm555.pdf.good luckandcheers to all

author: SmokeyTheElectrician
author_rank: Contributor
timestamp: December 22, 2019, 02:38:00 pm
content: Quote from: schmitt trigger on December 21, 2019, 12:50:37 amThe 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 ideawas to hold the right side timer in reset for half of a cycle of the left side timer and then letit run during the left side timer's other phase (output high). I think if the right hand circuitwould have been a one shot, the design would have been easier to decipher...Cheers to all

author: ebastler
author_rank: Super Contributor
timestamp: December 22, 2019, 03:03:05 pm
content: Quote from: phennessey on December 22, 2019, 01:53:34 amThat 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.

author: phennessey
author_rank: Contributor
timestamp: December 22, 2019, 06:27:27 pm
content: No, not the same diagram. I mean the same components. Can these components produce the effect?556 timer2x 100uF caps5x resistors with the values listed3 LEDs blinking in sequence (Gr long, Yl. short, Rd. long)

author: james_s
author_rank: Super Contributor
timestamp: December 22, 2019, 06:59:26 pm
content: I don't see how. You'd need to add at least something to allow you to hold the second timer in reset and also prevent either LED from lighting while the first one is on. As I mentioned earlier, this is an unusual way of doing a traffic light.

author: phennessey
author_rank: Contributor
timestamp: December 22, 2019, 07:35:22 pm
content: Besides a microcontroller, what’s a single simple IC that could do this? There are many 555 variants out there (like the 556), would any of those achieve this effect?

author: james_s
author_rank: Super Contributor
timestamp: December 22, 2019, 07:49:04 pm
content: Well you could use a pair of 555's as done in the original circuit. There's also the classic design using a decade counter and some diode 'or' logic.http://nickviera.com/electronics/traffic_simple/Countless other ways of achieving the same thing, most will start with something like a 555 to generate pulses and then some sort of counting logic.

author: phennessey
author_rank: Contributor
timestamp: December 22, 2019, 08:13:20 pm
content: Yes, but those use multiple ICs. Is there a single IC, besides a microcontroller, that can achieve this?

author: Zero999
author_rank: Super Contributor
timestamp: December 22, 2019, 09:02:40 pm
content: Quote from: phennessey on December 22, 2019, 08:13:20 pmThe schematic I posted previously can do it using a single IC, such as the 74HC14. Which pin goes where should be apparent when you've read the data sheet. Obviously the power pins 7 and 14 will need to be connected to 3V to 6V, with a 100nF decoupling capacitor across them.https://www.mouser.com/datasheet/2/308/74HC14.REV1-34947.pdfIf you must use the 555 timer, you can use them as Schmitt triggers to make the same circuit as I previously posted, but will need two or three ICs.

author: james_s
author_rank: Super Contributor
timestamp: December 22, 2019, 09:14:26 pm
content: Why are you obsessing about doing it with a single IC and avoiding a microcontroller? What is the goal exactly? Are you trying to learn a specific aspect of electronics? I microcontroller is the single IC solution, it's the smallest, easiest, cheapest way to go. A $2 attiny85 Arduino can do it with code that can be written in literally 2 minutes.Otherwise most solutions are going to take multiple ICs, or a single IC and some transistors and diodes, you can build a astable mulivibrator out of two transistors, two capacitors and 4 resistors. You might also try a ring oscillator out of transistors, or you could try the CD4060B which is an integrated counter/oscillator IC. You're going to have to experiment, that's part of the hobby.

author: SmokeyTheElectrician
author_rank: Contributor
timestamp: December 22, 2019, 09:36:51 pm
content: Quote from: phennessey on December 22, 2019, 07:35:22 pmWow and Holy Cow!,there is a ton of awesome advice herein all of these posts and replies.Thanks for sharing EEVBlog!I'll bet once the OP achieves success with 555type timers, you all have opened up an entireuniverse of discovery should the OP decide tofurther persue their interest in futzing aroundwith electronic circuitry.Now getting back to trying to follow the OP's initial and insistent request:Please redraw the circuit you originally shared with shared with us,according to my prior suggestions and post the new circuit so weare able to make sure we are on the same page.( even better, if you do not already have it downloaded and install. LT SPICE {or any other free SPICE version} and use that for. schematic capture and you will be able to also simulate the. circuit {and share those results} )Next take a look at the 555's and 556's pin assignments.. ( you already have a diagram for the 555 in the OP )... ( hint go on your favorite search engine and search LM556 Pinout )and construct a table as follows:( actually, here, I'll help you out a little more by getting the table started. just fill in the pin numbers from the 556 -- hint: since Vcc and Gnd are. share between the 2 556 timers, just repeat the 556's Vcc and Gndassignments in the below table for each timer )Function 555 556tmr1 556tmr2------------------ ----- ---------- ----------Ground 1Trigger 2Output 3Reset 4Control Voltage 5Threshold 6Discharge 7Vcc 8Then re-redraw the circuit using the 556 in place of the 555saccording to the above pin cross-reference map that you created.&&& again,share your results so we can help keep you on track,(as well as gloat with you once you achieve success....). ( BTW the ultimate goal here is to help you to learn to answer your own questions.... at which point you will start to be able to help noobier noobs on these forums.... as well as share the clever things you come up with the rest of us )Cheers to all!

author: SmokeyTheElectrician
author_rank: Contributor
timestamp: December 22, 2019, 10:05:45 pm
content: Quote from: james_s on December 22, 2019, 06:59:26 pmWith the circuit redrawn according to my earlier suggestions:.Timer 1 free runs&&&When timer 1's output is low:a) The Red LED lights......12v---/\/\/\---->|-------TMR2out(low)andb) timer 2 is held in reset where byb.1)the discharge transistor is off...(the Orange LED will be off : 12v---/\/\/\---->|-------disCHRg2(open) )andb.2)the output is low...(the Green LED will be off : TMR2out(low)-----/\/\/\--->|-------GND )Then when timer 1's output goes high:a) The Red LED will be off......12v---/\/\/\---->|-------TMR2out(high)andb) timer 2 can free runb.1) during the phase where TMR2output is low ( actually TMR2's 2nd half cycle )the discharge transistor will be on...(the Orange LED will be on : 12v---/\/\/\---->|-------disCHRg2(GND+Vsat -i.e. low) )...(the Green LED will be off : TMR2out(low)-----/\/\/\--->|-------GND )andb.2) during the phase where the TMR2output is High ( actually TMR2's 1st half cycle )the discharge transistor will now be off...(the Orange LED will be off : 12v---/\/\/\---->|-------disCHRg2(open) )...(the Green LED will be on : TMR2out(low)-----/\/\/\--->|-------GND )andc) the time constant for timer 2 is long enough such that timer 1 putsit back in reset before timer 2 starts on a second cycle.Cheers to all!

author: SmokeyTheElectrician
author_rank: Contributor
timestamp: December 22, 2019, 10:24:25 pm
content: PScircuit diagrams are compliments of ASCIICAD

author: SmokeyTheElectrician
author_rank: Contributor
timestamp: December 22, 2019, 10:44:37 pm
content: Corrections:a) I have typos where TMR2 should be TMR1b) the orange diode powers off of the Timer output+ c) some clarification in the operation of Timer2so lets see if I can spell out the circuit's operationwithout any more ooopsies:~~~~~~~~~~~~~Timer 1 free runs&&&When timer 1's output is low:a) The Red LED lights......12v---/\/\/\---->|-------TMR1out(low)andb) timer 2 is held in reset where byb.1) the 555's internal discharge transistor's state does not matter (it is either low or open)...(the Orange LED will be off : TMR1out(low)---/\/\/\---->|-------disCHRg2(do not care) )andb.2)the output is low...(the Green LED will be off : TMR2out(low)-----/\/\/\--->|-------GND )Then when timer 1's output goes high:a) The Red LED will be off......12v---/\/\/\---->|-------TMR1out(high)andb) timer 2 can free runb.1) during the phase where TMR2output is low ( actually TMR2's 2nd half cycle )the discharge transistor will be on...(the Orange LED will be on : TMR1out(high)---/\/\/\---->|-------disCHRg2(GND+Vsat -i.e. low) )...(the Green LED will be off : TMR2out(low)-----/\/\/\--->|-------GND )andb.2) during the phase where the TMR2output is High ( actually TMR2's 1st half cycle )the discharge transistor will now be off...(the Orange LED will be off : TMR1out(high)---/\/\/\---->|-------disCHRg2(open) )...(the Green LED will be on : TMR2out(high)----/\/\/\--->|-------GND )~~~~~~~~~~~~~sorry for the additional confusion

author: phennessey
author_rank: Contributor
timestamp: December 22, 2019, 10:48:17 pm
content: For the ring oscillator, can the timing be altered between each LED flash by changing resistance values?

author: phennessey
author_rank: Contributor
timestamp: December 22, 2019, 10:53:42 pm
content: It isn’t an obsession, it’s just that I feel like a microcontroller is cheating. It’s too easy! (That being said, I ordered one anyway.) I’m going for “simple” and “elegant” solutions with common discrete components and basic ICs

author: phennessey
author_rank: Contributor
timestamp: December 22, 2019, 11:00:18 pm
content: That’s great, but did you try it using a 556 timer instead?Apparently it’s impossible!

author: SmokeyTheElectrician
author_rank: Contributor
timestamp: December 22, 2019, 11:49:24 pm
content: Quote from: phennessey on December 22, 2019, 11:00:18 pmIf the above is in reply to my responses,either you did not carefully read through all of themor am I being trolled?Everything needed to get your circuit functioning as youoriginally requested has been covered in my posts ( asidefrom maybe some typo or other mistake in communication ).It is left for you to take the help I have offered andhelp yourself by redrawing your circuit using a single556 in place of the two 555's.

author: phennessey
author_rank: Contributor
timestamp: December 23, 2019, 02:20:41 am
content: I’m not trolling, I just thought it had been established (by others in this thread) that this circuit cannot be done with a 556, because the power to the second 555 comes from the output of the first 555, and that cannot be replicated with a 556, which only has one +V input. I thought your instructions were using two separate 555s.Frankly, most of this is over my head. I have ordered the parts and I plan on tinkering. I’ll even sketch an attempt (I don’t have any circuit software, so I’m drawing stuff with Adobe Illustrator.) I was just hoping someone would sketch out a 556 timer circuit so I could try to translate it to a breadboard. I initially thought this would be a simple enough request that it would just be matter of re-drawing a couple lines in the first diagram I posted (which I did not make, nor do I fully understand.)Regardless of what happens, I plan on building this thing and I don’t care how long it takes me! Parts are ordered and that’s that!I plan on attempting this circuit in 4 different ways:1. 2x 5552. 1x 5563. 1x 74hc14 (ring oscillator)4. attiny85 (I ordered the usb programming board, too)Everyone’s help has been incredibly valuable. I will post results here!

author: electricMN
author_rank: Regular Contributor
timestamp: December 23, 2019, 03:05:40 am
content: Quote from: phennessey on December 23, 2019, 02:20:41 amDownload Kicad for creating your schematics. It's free.

author: SmokeyTheElectrician
author_rank: Contributor
timestamp: December 23, 2019, 03:34:11 am
content: Quote from: phennessey on December 23, 2019, 02:20:41 amWith some minor change to the circuit, it can be done.Quote from: phennessey on December 23, 2019, 02:20:41 amMy apologies, with the schematic you presented, I over estimated your level of experience.Quote from: phennessey on December 23, 2019, 02:20:41 amstay tuned ( I misunderstood and thought you wanted corrections so you could draw it )Quote from: phennessey on December 23, 2019, 02:20:41 amthat's the spiritQuote from: phennessey on December 23, 2019, 02:20:41 amagain, stay tuned&I look forward to seeing your posts as you realizethe other versions of the circuitQuote from: phennessey on December 23, 2019, 02:20:41 amI entirely agree

author: SmokeyTheElectrician
author_rank: Contributor
timestamp: December 23, 2019, 04:39:22 am
content: Ok, here is the original circuit entered in LT SPICE( LT SPICE is free for all to use, when you feel ready,you can get off of Linear's website:https://www.analog.com/en/design-center/design-tools-and-calculators/ltspice-simulator.html)--Notice the 555's symbol follows the actual chip's pinout.Also I modified the LEDs' current limiting resistors to have the LED current under 20mA.When I ran the simulation, it does not quite work.The orange LED stays on through the red LED's phase.

author: SmokeyTheElectrician
author_rank: Contributor
timestamp: December 23, 2019, 05:26:46 am
content: Studying the waveforms from the prior post:Notice I_red_led follows Timer1's output (Vtmr1), but is invertedAlso notice I_green_led follows Timer1's output (Vtmr2).Then there is that space in time between when I(D_red) and I(D_green) is flowingwhere we would like current to flow in the Orange LED - I(D_orange).We ask ourselves is there anything unique in the relationship between12v, Vtmr1, Vtmr2, and ground during that time interval that does not( edit: /\ Discharge1, Discharge2, )exist during the interval when the Orange LED should be off?Well if you drive the Orange LED with Timer1 and sink it with Timer2,you may observe Vtmr1 is high and Vtmr2 is low during the timeand only during the time the Orange LED should light up.For all other time intervals Vtmr1 and Vtmr2 are both either high or lowsimultaneously.Ideally (other than that glitch) the waveforms we would like are as follows:The only modification (correction to your drawing?) to the circuitwas to re-route the high side of the Orange LED circuit from 12v tothe Timer1 output ( V(tmr1)), like in the following diagram:

author: SmokeyTheElectrician
author_rank: Contributor
timestamp: December 23, 2019, 06:20:14 am
content: You may recall Mr "schmitt trigger" pointed out in post 3 that Timer2 was powered by Timer1's output.( generally bad form as small form IC outputs generally to not have the capacity to supply much current )Then in post 15 Mr "schmitt trigger" advised exploring not powering up Timer2 in the above manneras well as exploring what the 555's Reset functionality may do for us.I made a quick scan of the datasheet for reset operation.According to what I read and saw on the block diagram, reset is an active low input, upon which theoutput would go low ( no current {=== no light} possible for the green LED)and the internal open collector discharge transistor would be de-energized(off ---> orange LED off).Hmmm,the Red LED is wired to be on when Timer1 Output is lowif that signal is fed into Timer2's reset, both the green and orange LEDs will stay offbecause the second 555 is held in the reset state.Then when Timer1 goes high, the red LED will turn offand Timer2 will be enabled and operate as discussed inposts 17, 27, and 29 (29 has corrections to 27).Ok, by now we see that we would like the second 555 powered off of 12vandit's reset pin driven by Timer1's output, like in the following schematic:( the waveforms are almost exactly the same as the last set posted. -- timing is the same, just Vtmr2 and associated currents are different due to the more proper voltage supply for 555 #2 )Now this circuit is entirely realizable in a single 556.

author: phennessey
author_rank: Contributor
timestamp: December 23, 2019, 06:43:46 am
content: Then the 556 is a piece of cake! Just remove the Vcc and ground from the second 555, and that’s basically it!Can’t thank you enough for your work on this. I just had this sneaking suspicion that the reset on the 2nd 555 could be useful.

author: phennessey
author_rank: Contributor
timestamp: December 23, 2019, 09:44:21 pm
content: Here’s my attempt at a hand-drawn 556 circuit. I’m on vacation so this is as good as I can manage for the moment. Let me know if this is correct? I’m sure I botched something somewhere, and drew this inefficiently or just incorrectly. I’m not sure what I’m allowed to move. I’m trying to picture current flowing through this circuit and trying to think about what relationships I need to keep and which ones are flexible. This was a mind-melting exercise.

author: SmokeyTheElectrician
author_rank: Contributor
timestamp: December 24, 2019, 04:57:19 am
content: With a quick glance, it looks good to me.This is a really simple circuit, but / however,formally, you could create netlists for both circuits,then cross reference them to each other andaffirm all the components pins are connected tothe equivalent nodes between the two circuits.

author: phennessey
author_rank: Contributor
timestamp: December 25, 2019, 02:37:53 am
content: No idea what a net list is or how to build oneI’ll get googling!My main concern was that I had fundamentally changed part of the circuit somewhere (changed a component from series to parallel, changed the order of something, etc).

author: james_s
author_rank: Super Contributor
timestamp: December 25, 2019, 04:17:39 am
content: A netlist is just a list of nodes (such as pins on ICs) and what connects to what. You draw the schematic in the schematic editor and it creates the netlist for you, you don't have to directly manipulate it.

author: phennessey
author_rank: Contributor
timestamp: December 25, 2019, 01:31:23 pm
content: I don’t have any EDA software (yet). I plan on getting a copy of Fritzing soon.

author: SmokeyTheElectrician
author_rank: Contributor
timestamp: December 25, 2019, 02:35:49 pm
content: Quote from: james_s on December 22, 2019, 06:59:26 pmYeah,I mostly agree,but I would bet a pack of Big League Chew( and as a matter of trivia of sorts )that at least some of the first traffic light circuitshad more in common with the OP's original schematicthan most of what was given as advice ( that is notto say there was anything wrong with any of thatadvice, quite the contrary, you all totally pointed the OPin the right direction for when they become interestedin tackling more complex circuit applications).In those original traffic lights I am thinking of,you'd likely find pneumatic delay relays functioningas the timer elements in a string of one shots connectedin a ring (think of a ladder logic implementation).cheers&&&Merry Christmas to everybody

author: schmitt trigger
author_rank: Super Contributor
timestamp: December 25, 2019, 10:13:57 pm
content: Back in the early 70s, I worked for a summer for the city’s traffic light department, in maintenance.There were a couple of systems, that I remember:-Relay ladder logic as you described.-A camshaft driven by a 1RPM geared synchronous motor.

author: james_s
author_rank: Super Contributor
timestamp: December 26, 2019, 04:32:34 am
content: There's lots of information out there about traffic light controllers, at least the stuff used in the US. Eagle, Econolite and Crouse-Hinds were some of the big makers here. Early systems used motor driven timing wheels and solenoids, then in the early 80s microprocessor based controllers started taking over.https://northstarhighways.wordpress.com/2016/09/10/how-traffic-signal-controllers-work-part-1-an-overview-of-controllers/

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: December 26, 2019, 05:04:40 am
content: Quote from: schmitt trigger on December 21, 2019, 06:15:45 pmPart of the enjoyment of visiting England and driving around there is that country's feature of the traffic lights facing you goes amber/orange prior to turning green. This gives the motorist time to extract a finger and put the vehicle in gear.Returning home, it's always a disappointment that we cannot implement such an innovation here. I once asked someone who works in the transport ministry why we can't manage it? A blank, short-circuited look for a few seconds and then the response: "Oh, cost."

author: phennessey
author_rank: Contributor
timestamp: December 26, 2019, 12:43:32 pm
content: Unpopular opinion: That’s a bad idea. Giving people an exact preview of when the light will turn green is only allowing the possibly for abuse and increases the chance for a collision.

author: james_s
author_rank: Super Contributor
timestamp: December 26, 2019, 04:55:56 pm
content: Quote from: phennessey on December 26, 2019, 12:43:32 pmHow so? You can already get this exact preview if you look at the lights on the cross street. Only an idiot steps on the gas before visually confirming the intersection clear, and the point of the amber light before red is to ensure the intersection is clear before the other direction gets a green. The fact that there are always a few idiots incapable of following the rules is a constant either way.

author: phennessey
author_rank: Contributor
timestamp: December 26, 2019, 06:29:30 pm
content: Idiots exist, ergo, why give them more ways to be idiots? Sometimes people run red lights. Why give people an incentive to gun it just when the light turns green? It’s certainly notsaferto give people advance notice of a green light.

author: SmokeyTheElectrician
author_rank: Contributor
timestamp: December 26, 2019, 06:56:59 pm
content: Quote from: james_s on December 26, 2019, 04:32:34 amQuote from: schmitt trigger on December 25, 2019, 10:13:57 pmThanks for the insights and link to the interesting reading / vidoes.

author: james_s
author_rank: Super Contributor
timestamp: December 26, 2019, 08:12:11 pm
content: Quote from: phennessey on December 26, 2019, 06:29:30 pmBecause it gives people a heads up so they are prepared to go, it's nice to have a chance to put the car in gear before the guy behind starts having a cow. I'm just not seeing this incentive to gun it created by a warning, can you find me some data showing it happens in any of the places where this is commonplace? Someone who is going to gun it at a green light is going to do so whether they have a yellow light or not.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: December 26, 2019, 08:45:05 pm
content: In my part of the ant hill, many peeps run red lights -because- often most drivers aren't ready to go anyway.

author: phennessey
author_rank: Contributor
timestamp: December 27, 2019, 03:40:33 am
content: If you know exactly when the light will change, you will be encouraged to not slow down as you approach a red light and try to time your entry into the intersection precisely when the light changes. Meanwhile, a car may be trying to get through the light before it turns red. Bad combination.I don’t have data, sorry! It just seems like a bad idea to give people advance notice when a light will turn green, which is why the US doesn’t employ that system. I can’t believe it would be safer with that feature, but I welcome any data that proves me wrong.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: December 27, 2019, 05:42:17 am
content: Quote from: phennessey on December 27, 2019, 03:40:33 amSometime in our near future, you're forgetting, all traffic light sets will have cameras. It used to be that bad intersections received a camera. Now, at the least, the road triggering infrastructure is being built into the roads with every new set. If the red light runners are indeed as bad as you say, my information suggests that revenue from tickets will pay for a camera installation at every turn.

author: james_s
author_rank: Super Contributor
timestamp: December 27, 2019, 07:29:32 pm
content: I would support red light cameras if they were about improving safety but unfortunately they end up being purely for revenue. Multiple municipalities have been caught turning down the amber light intervals and data has shown rear end accidents to increase at camera equipped intersections. In a city near me there was an attempt to put forward a citizen initiative banning red light cameras and it got shot down early in the process with an official quoting that they need the revenue.

author: james_s
author_rank: Super Contributor
timestamp: December 27, 2019, 07:35:19 pm
content: Quote from: phennessey on December 27, 2019, 03:40:33 amSorry but if you don't have data then it is just baseless speculation and of no value, it makes me suspect you have never driven anywhere that has this feature. All it does it illuminate the amber light for a brief period just before it turns green, it gives you just enough of a warning to have time to put the car in gear, it's very convenient and doesn't cause the problems you believe it does. You still look both ways to verify that traffic has stopped on the cross street before proceeding, just like you (hopefully) do anywhere else.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: December 27, 2019, 11:22:35 pm
content: Quote from: james_s on December 27, 2019, 07:29:32 pmYeah.It's good that it is being admitted to. You can now get down to brass tacks on how much they receive and how much they waste.

author: james_s
author_rank: Super Contributor
timestamp: December 28, 2019, 01:17:05 am
content: I don't think they meant to admit it, it was more one of those "Whoops, said that out loud" moments that ended up getting quoted in the article.It would bother me a bit less if they just were forward about it being about revenue, I'm fine with a tax on people who can't follow the rules and running red lights is a particularly annoying not to mention dangerous habit that has been increasing. Shortening amber light intervals is BS though, they have to know that will increase accident rates, they should have generous amber intervals so that people have time to stop safely without slamming on their brakes and getting rear ended by the guy behind them who thought they were going to gun it through the yellow, that is, if the goal was actually improving safety. I'm also not fond of the fact that our red light cameras are normally run by a private out of state company that skims a substantial profit, and they are not normal traffic tickets so they are much harder to contest in court than a ticket from a police officer.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: December 28, 2019, 01:51:19 am
content: What is a crime is that you got to 10k posts before I got to 1k.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: December 28, 2019, 01:52:44 am
content: But there's still time..

author: SmokeyTheElectrician
author_rank: Contributor
timestamp: December 29, 2019, 03:22:01 pm
content: Quote from: james_s on December 27, 2019, 07:29:32 pmWow,the official was not firedplus no injunction against the city?Around my neck of the woods,at least they have delayed the green,as they know everyone is racing it toget through those amber signals.With all the "AI" going on these days,you'd think they would use those traffic light camerasto intelligently delay ( or not ) the greendepending on whether or not the cross traffichas stopped ( or is not even present ).I've never heard it discussed,but the concept of an amber go zone( if this zone is ahead of you when the light turns amber,do not even think about gunning it, get on the brakes )should be integrated into driver's educationas well as marked out with striping acrossthe roadway and signage to the side, plusmaybe even a sign strung above the roadway.It does not take a genius (no offense to any traffic engineers)to figure out how far such indications should befrom the intersection (including a decent safety margin -- there areonline esitmaters that include reaction time and etc...)(there could also be an earlier {further before the intersection}indication for wet conditions or whatever is found to increase safety )I guess no governing body would actually do thisas the lawyers would get their greedy fingers inthere as someone is gonna figure out how toto create a wreck no matter what.Well, then there are those traffic circulationspopping up more and more that seem tobe working out pretty well in most cases....

author: james_s
author_rank: Super Contributor
timestamp: December 29, 2019, 05:16:45 pm
content: Quote from: SmokeyTheElectrician on December 29, 2019, 03:22:01 pmNope, in at least one case they tried to fine the guy $500 for calling himself an engineer without being a certified professional engineer.https://interestingengineering.com/calling-himself-engineer-got-this-man-fined-500

author: themadhippy
author_rank: Super Contributor
timestamp: December 29, 2019, 05:34:54 pm
content: Quotedont go to Thailand then,not only do you have the pretty lights but also a countdown timer showing how long each aspect has to last

author: Zero999
author_rank: Super Contributor
timestamp: December 31, 2019, 09:55:51 am
content: Quote from: SmokeyTheElectrician on December 29, 2019, 03:22:01 pmWe also have delayed green. The problem is it encourages people to jump the lights when they realise it's still red on the other side and go anyway. Turning red a little early and green a bit late are good safety features, but they shouldn't be too long, otherwise it makes it more dangerous and frustrates drivers.

author: schmitt trigger
author_rank: Super Contributor
timestamp: December 31, 2019, 04:32:22 pm
content: It seems that different countries have different ideas to discourage bad driving behaviors.That is the reason a microcontroller based system is so powerful. Different rules may be easily implemented.We have drifted far, far away from the OP’s topic.

author: phennessey
author_rank: Contributor
timestamp: January 06, 2020, 06:01:32 pm
content: Quote from: Zero999 on December 21, 2019, 09:54:31 pmI don't understand a lot of these symbols, can you help me identify the arrows and the "I1" and "O1" tags? Are those supposed to be probe points? And I don't understand the arrow symbols. Are those all ground? I thought a schmitt trigger had one input and one output. But this circuit is showing all the triggers with arrows pointing out of them, which is deeply confusing to me. The 74HC14 only has volts in and out, plus six triggers, all of which only have one input and one output. But you drew this diagram with ground terminals on every trigger. Can you explain this a bit?I tried to redraw your circuit...did I goof?

author: hermitengineer
author_rank: Regular Contributor
timestamp: January 07, 2020, 08:09:15 am
content: A ring oscillator doesn't do the traffic light though. Around the ring you'll find that each LED is a toggle of the one before it. Since it's a ring with an odd number of inverters, there will be a toggler running down the ring toggling each LED as it goes. So effectively, you always have about 2 LEDs lit, as seen in the waveforms that were simulated. You need a ring one-shot instead. Maybe something like this:

author: phennessey
author_rank: Contributor
timestamp: January 07, 2020, 06:19:22 pm
content: Not true at all. I'm literally staring at a completed circuit that is lighting up exactly the way I want (I just had to change some resistance values to introduce an instability in the cycle.)

author: hermitengineer
author_rank: Regular Contributor
timestamp: January 07, 2020, 06:44:49 pm
content: Quote from: phennessey on January 07, 2020, 06:19:22 pmI was wondering if the odd LED hookups were done to eliminate the extra LED in the ring. Apparently so. If the LEDs were hooked up in a conventional way (each output to a resistor and LED to ground), then you'd see the typical ring oscillator pattern.