I need to make an LED arrow with 5 LEDs. These are the charateristics:
-The overall period is 2s
-The arrow is off for 0.5s
-At 0.5s LED 1 turns on and stays on for 1.5s
-At 1.0s LED 2 turns on and stays on for 1.0s
-At 1.5s LEDs 3, 4, and 5 turn on and stay on for 0.5s
-The process repeats indefinitely
-The timing should be accurate to ±25msec

The LED arrow looks like this:
-->
LED 1 and 2 form the straight line and 3, 4, and 5 form the head.

I was planning to use 555 timers, if 555 timers is the best way to go then how would I make this happen?

Thanks

 

Use 555 to generate 500mS timing and send them to 1 or 2 4017 in cascade. OR the outputs with 1N4148 if you need more than 0.5 seconds.

Invert all output with ULN2003 and drive the LED in sinking mode.

Allen

 

Use 555 to generate 500mS timing and send them to 1 or 2 4017 in cascade. And the outputs with 1N4148 if you need more than 0.5 seconds.

Invert all output with ULN2003 and drive the LED in sinking mode.

Allen

I'm only allowed to use stuff from a kit I was given and I don't have 4017, I have 555 timers and transistors(2N3904, 2N3906, 2N7000, TP0606)

 

I'm only allowed to use stuff from a kit I was given and I don't have 4017, I have 555 timers and transistors(2N3904, 2N3906, 2N7000, TP0606)

That's a strange limitation for what you need to do.
I count six 555 timers to do what you want.
The transistors an be used to drive the LEDs from the 555 outputs.
To get 25ms accuracy you will likely need to use pots to adjust the timing of each 555.

 

You can use this 555 calculator to calculate the 0.5S, 1S etc. timings that you want.

And here is how I do it using 555 and 4017 to accomplished the task. See if you can get any ideas out of it.


Allen

 

You can use this 555 calculator to calculate the 0.5S, 1S etc. timings that you want.

And here is how I do it using 555 and 4017 to accomplished the task. See if you can get any ideas out of it.

View attachment 139771
Allen

Thank you! So far I've been using three 555 timers. The initial 555 timer I set it to have a period of 2s and then I'm connecting two 555 timers with transistors to the output of the first 555 timer. For one of the newly added 555 timers I'm setting T high to be 0.5 since 3 LEDs have the same behavior. I have no idea how to use the other added 555 timer for LED 1 and 2. I wish LED 1 and 2 could go off when the other goes on that would make things easier but unfortunately it's not an allowed specification

 

The way I see it, the easiest is to use two 555's for each set of LED periods.

 

Thank you! So far I've been using three 555 timers. The initial 555 timer I set it to have a period of 2s and then I'm connecting two 555 timers with transistors to the output of the first 555 timer. For one of the newly added 555 timers I'm setting T high to be 0.5 since 3 LEDs have the same behavior. I have no idea how to use the other added 555 timer for LED 1 and 2. I wish LED 1 and 2 could go off when the other goes on that would make things easier but unfortunately it's not an allowed specification

The difficult part is how to synchronize the three 555 timers. You can either use the "reset" or "trigger" to start the next 555.

I have not thought hard enough on using 2-3 timers. May be tomorrow I can cook up something after jogging with my friends.

Allen

 

The difficult part is how to synchronize the three 555 timers.

All timers are started by the end of the LED 3, 4, & 5 timer.
Then all three sets of LED timers (two 555's per LED) do their thing simultaneously, i.e.:

• LED 1 has 0.5s delay followed by 1.5s ON.
• LED 2 has 1.0s delay followed by 1.0s ON.
• LEDs 3, 4, and 5 have a 1.5s delay followed by 0.5s ON.

The falling edge of the LEDs 3, 4, and 5 ON pulse triggers all the delay 555s to start again.

 

All timers are started by the end of the LED 3, 4, & 5 timer.
Then all three sets of LED timers (two 555's per LED) do their thing simultaneously, i.e.:

• LED 1 has 0.5s delay followed by 1.5s ON.
• LED 2 has 1.0s delay followed by 1.0s ON.
• LEDs 3, 4, and 5 have a 1.5s delay followed by 0.5s ON.

The falling edge of the LEDs 3, 4, and 5 ON pulse triggers all the delay 555s to start again.

With your description, I am sure the TS is able to design it now.

Allen

 

With your description, I am sure the TS is able to design it now.

Allen

I hope a design can be made to meet these requirements, I'm trying to come up with ways to synchronized my 555 timers but I can't manage to do it.

 

I'm trying to come up with ways to synchronized my 555 timers but I can't manage to do it.

Did you not understand my description of how they are all synchronized at the start?
Do you understand how a 555 works?
If so, you should be able to determine how to synchronize and trigger one 555 from another's output.

 

Just wondering -- how much of this student's homework is left for THEM to design?

 

Did you not understand my description of how they are all synchronized at the start?
Do you understand how a 555 works?
If so, you should be able to determine how to synchronize and trigger one 555 from another's output.

I do understand how a 555 timer works, my question is since I'm going to be using many 555 timers, what should I make T high and T off for the first 555 timer?

 

I did it. Using the method suggested by @crutschow . And here's the scope trace on my simulator.

You should be able to do it. I am not going to show the schematics and spoil all your fun....


Allen

 

I do understand how a 555 timer works, my question is since I'm going to be using many 555 timers, what should I make T high and T off for the first 555 timer?

Have you put some thought on How to use the 555 as a monostable multivibrator?

Allen

 

Just wondering -- how much of this student's homework is left for THEM to design?

Well we've given him more than we should probably, but he still doesn't seem to know how to do it.

 

I do understand how a 555 timer works, my question is since I'm going to be using many 555 timers, what should I make T high and T off for the first 555 timer?

You gave us the times you need in your first post.
Why are you asking us what they should be?

If you know how to make a 555 into a one-shot (monostable), then the info I gave you in post #9 should be sufficient for you to determine that time and go from there.
Draw a block diagram of how all the 555's would be connected together, and what each will do.
That will help you determine what needs to be done in the circuit.

 

You gave us the times you need in your first post.
Why are you asking us what they should be?

If you know how to make a 555 into a one-shot (monostable), then the info I gave you in post #9 should be sufficient for you to determine that time and go from there.
Draw a block diagram of how all the 555's would be connected together, and what each will do.
That will help you determine what needs to be done in the circuit.

Sorry but in my class, we've barely talked about 555 timers. All this monostable and astable mode, I just learned it yesterday cause I was doing my own research. On a side note, you said on post #9 "two 555's per LED" and I wasn't provided with ten 555 timers I only have five 555 timers.

 

Put the whole parts list that you have in the kit. Then the members can see what your limitations are.

Dont forget to place the quantity next to each item.