#### Kaito

Joined Nov 8, 2019
5
I want to build a circuit with 2 LED that blink alternatively with a delay
Like this:
0.25s: LED1 on, LED2 off
0.5s: both LED off
0.25s: LED1 off, LED2 on
0.5s: both LED off
And the cycle repeat.
First, I think I will use 555 timer, but I can't figure out how to make the 0.5s pause.
Do you guy have any idea?

#### dl324

Joined Mar 30, 2015
9,142
Welcome to AAC!
First, I think I will use 555 timer, but I can't figure out how to make the 0.5s pause.
Do you guy have any idea?
Is this a school project? Do you care what other components are used?

#### Kaito

Joined Nov 8, 2019
5
This is a school project. I can't use microcontroller, FPGA or other digital devices.

#### dl324

Joined Mar 30, 2015
9,142
This is a school project.
For school work for which you will receive a grade, members can only offer guidance. Show your ideas so we can see where you're getting stuck.
I can't use microcontroller, FPGA or other digital devices.
Does digital devices include logic gates?

#### jpanhalt

Joined Jan 18, 2008
8,099
As this is homework, what solution(s) have you come up with?

#### Kaito

Joined Nov 8, 2019
5

This is my first design. I can make the LED 1 and LED 2 blink alternatively. But I don't know how to add the pause time in between.

#### Kaito

Joined Nov 8, 2019
5
For school work for which you will receive a grade, members can only offer guidance. Show your ideas so we can see where you're getting stuck.
Does digital devices include logic gates?
No logic gates

#### jpanhalt

Joined Jan 18, 2008
8,099
You can't do what you describe with a single 555. Try having one 555 trigger another or use logic.

#### dl324

Joined Mar 30, 2015
9,142
No logic gates
You can't do it with a single 555 timer. Please post the entire text of the problem.

#### GeorgeBC

Joined Mar 22, 2019
2
I would observe that on the basis of a 0.25 second tic rate your outputs for LED1 and LED2 are as follows:
T LED1 LED2
0 1 0
1 0 0
2 0 0
3 0 1
4 1 1
5 1 1

LED1 is basically a single clock delay of LED2. So concentrate on constructing the LED2 sequence then run that output through a single D flip flop to get the LED1 output. You can use your 555 timer to generate the 0.25 second oscillator that drives the clock input of the flip flop.

#### dl324

Joined Mar 30, 2015
9,142
Code:
T  LED1   LED2
0    1      0
1    0      0
2    0      0
3    0      1
4    0      0
5    0      0

#### BobaMosfet

Joined Jul 1, 2009
836
This is a school project- the objective is for you to figure these things out. IN electronics, the most basic way to introduce a delay is using a capacitor and a resistor-- there are formulas to help you figure out the time constant. I recommend learning about capacitors, and picking a specific value, and then learning how to calculate the resistor size, so you get the time delay you want.

#### Bernard

Joined Aug 7, 2008
5,288
If you can use some discrete parts, C s R s, & diodes ? then a 4 stage 555 ring counter can be made
Each 555 triggers on pulse trailing edge via R/C to next 555 input. Might want to provide a startup reset. Start is taking first stage , pin 2 lo momentarily.

Last edited:

#### ci139

Joined Jul 11, 2016
791
The direct answer with the circuits had been deleted, because it doesn't allowed in Homework Help forum, if any Helpers provides the direct answer for the TS then he may get ban from this Homework Help forum.

Last edited by a moderator:

#### ericgibbs

Joined Jan 29, 2010
8,873
hi,
Please bear in mind this Thread is in the Homework Forum and so the help we give should be limited to guidance for the TS, not final solutions.

Moderation.

#### ScottWang

Joined Aug 23, 2012
6,832
use two timers then combine the signals for your led drivers -- as the counters can't be used the most likey option is the other timer being 1-shot retriggerable
the whatsoever transition trigger goes like -- See the Simulation
/¯¯¯¯¯¯¯\_______/ A=Timer 1
/¯¯\____/¯¯\____/ B=Timer 2
/¯¯\____________/ A·B
________/¯¯\_____ A̅·B
Please take a look on #2.
When a member keeps on giving direct answers to the Homework Help section, the moderating staff will start a discussion if a ban from the Homework Help section will be applied to that member.

#### Bernard

Joined Aug 7, 2008
5,288
At the bottom of this page find, Similar Threads, short way down to Getting a ball to glow---.
might find something useful, see faulty drawing post #9.