Traffic Lights with Relays and Timers

Thread Starter

MonteWolff

Joined May 11, 2018
5
I am looking for help designing a control system using relays and timers to control 2 sets of traffic lights that sequence based on time. Any ideas?
 

eetech00

Joined Jun 8, 2013
3,961
I am looking for help designing a control system using relays and timers to control 2 sets of traffic lights that sequence based on time. Any ideas?
I might be able to help..

What are your design requirements?
Suppy voltage?
Relays only?
4 way?
No of aspects?

Etc...

eT
 

Thread Starter

MonteWolff

Joined May 11, 2018
5
I might be able to help..

What are your design requirements?
Suppy voltage?
Relays only?
4 way?
No of aspects?

Etc...

eT
Hello - thanks for your reply
I am looking to control 6 120 VAC lights assembled in two sets of Red / Amber / Green. The objective is to run these lights like regular traffic lights with sequence based on time alone (no external sensors). I have 4 time delay relays (11 pin), 4 control relays (11 pin) and 2 control relays (8 pin). I would like the control circuit to run off of 24 VDC. The objective of this exercise is for students to understand how relays function and how you can use dual voltages. I have the schematic for some of it, but have run into the issue of "moving" from one cycle to the next. The attached is a start to the schematic. Thank you.
 

Attachments

MaxHeadRoom

Joined Jul 18, 2013
28,702
Maybe also explain or show to them the importance of cross interlocking in a system such as this.
Also the ladder logic you are using is a good exercise in Boolean logic.
Max.
 

crutschow

Joined Mar 14, 2008
34,470
If this is for students, I would not use 120VAC unless you have an isolation transformer for safety.
Otherwise the liability issues are high.

If you want to use two supplies, just use two different low voltage supplies, such as 12V and 24V.
Much safer.
 
I totally agree with @crutschow. If you really want ton use 120 VAC traffic lights use 3-32 V SSR relays.

You can substitute LEDs while breadboarding and then finally connect to the 3-32 V control system. All of the 120 V stuff is safely tucked away.

While 24 VDC sounds good, you might have better luck using a lower voltage.

The traffic light sounds more like an Asyncronous machine with timers, but I don;t know.

Assume one light is the master: You have the red delay and then the amber/green delay. When red times out, you have the amber green delay system.

On the falling edge of the master RED, you do a yellow/green cycle on the slave.
On the Rising edge of the master yellow, the slave is RED

That's my quick an dirty timing without the delays. I know stuff is missing.
 

Thread Starter

MonteWolff

Joined May 11, 2018
5
I totally agree with @crutschow. If you really want ton use 120 VAC traffic lights use 3-32 V SSR relays.

You can substitute LEDs while breadboarding and then finally connect to the 3-32 V control system. All of the 120 V stuff is safely tucked away.

While 24 VDC sounds good, you might have better luck using a lower voltage.

The traffic light sounds more like an Asyncronous machine with timers, but I don;t know.

Assume one light is the master: You have the red delay and then the amber/green delay. When red times out, you have the amber green delay system.

On the falling edge of the master RED, you do a yellow/green cycle on the slave.
On the Rising edge of the master yellow, the slave is RED

That's my quick an dirty timing without the delays. I know stuff is missing.
Thank you for the notes.
 
It's not meant to be complete.

To round out the course, I would also consider introducing a "Smart relay' such as those from idec and others.

The students could do the entire project using simulation. You could have one real "smart relay" that the students could actually program.

There are other manufacturer's. The right one might introduce visual programming, ladder logic and even statement type programming.
Do a little research.

This way, a lot more stuff is taught such as the cost effectiveness of a design.

In an industrial environment, we want as little "glue" as possible. "Making from scratch" is not usually an option.

==

Aside: I tried unsuccessfully to convince management to create a system that would save us a day or more worth of unnecessary work if the power died for more than 5 minutes. In other words, the shutdown procedures differ for short power glitches. Different vacuum systems. One type was diffusion pump based and the other cryopump based.

We put the cryopump on the back-up generator until, it had to be removed (it was a convienience load) when other essential loads were added.

Valves are involved. Possibly heaters and water.

I could not swing it because management said power failures were infrequent.
 
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