Time delay circuit, help needed

[Love Electronics]

I have done this circuit in multisim 9, its a 10 LED sequencer,  it goes on sequence for ever. How can I introduce a time delay circuit say for couple of secounds. I beleive another 555 timer will do, but where and how to connect the whole circuit then?

[lacy]

I will try this one as I have done a simular circuit before. Using your second 555 timer theory, you could insert the output of the 555 timer into the MR input of the 4017 through a transistor. and a 1k resistor to positve voltage This would hold MR to ground until the timer timed out and then would reset the 4017 and keep it off until the second timer was re-triggered. This would have to be a monostable arrangement and I am not sure how you would want to trigger it. You could trigger it from one of the ouputs after inverting it or you could manually trigger it. This is something you would have to work out.

It would be more efficient from a layout standpoint if instead of 2 555 timers to use one 556 timer. This is a matter of choice that only you can decide.

I am sure there may be better methods or maybe even simpler methods that someone else may have come up with. If so, I would hope they would post their ideas to this forum.

I hope I was of some assistance and I hope you get your circuit working the way you want it to. Good Luck

[lacy]

I just entered your circuit into my version of Multisim. I used the second timer to reset the 4017. The only problem is that I tried triggering the second 555 in various ways and the only one that worked was to manually trigger the second timer with a switch to ground and a 1k resistor to positive with pin 2 tied in between them. It cycled for 2 seconds and then shut down the 4017 until I re-trigged it via the switch.

I hope this helps. If you would come up with a different solution, please let us know how you did it. That would help others who may have run into the same situation..

[Love Electronics]

Thanks Lacy for your reply, could you plz send me the file in multisim or picture format.

[lacy]

I am using Multisim 2001 so I am not sure that the file will be able to be opened with Version 10, but I am going to post it and hope for the best. I can't figure out how to get a screenshot of the circuit so maybe you could help me with that.

Here's my file:

Just a note. I used a bar graph diisplay instead of the LEDs, but it will work with your LEDS. It was just easier to use the bar graph display than to wire up ten LEDs. Also, just so you'll know,  the first output pin on the 4017 represents zero and will always stay on if there is no input pulse to the clk line of the 4017 or held in reset. When I wire up a circuit like this I usually don't use the first ouput and start with the next one. I wired it in here so you could see what I am referring to.

Message Edited by lacy on 06-28-2007 09:00 PM

[AbuMohamed]

Message Edited by AbuMohamed on 06-29-2007 04:43 AM

[Love Electronics]

Thanks Lacy for ur help, really appreciate it. I just rename the file to my ms9 and its open, But the circuit didn't work properly.
The secound timer act like its not there, if i am to press the swith each time i want to stop the sequence. If that the case I could better use a double pole switch connected between logic high and GND and toggle between them each time i want to stop the sequence. Thanks dear.

About how to do a pic of ur drawing, just sellect all, copy them, and then paste them in paint or whatever software u use for editing pictures, or use the print screen.

Cheers

[lacy]

The way I did this may be different than what you need. In my circuit, you press the button the second timer to start the sequence and it times for 2 seconds and automatically shuts down. If you need to stop the sequence once it has started, then I need to think about that one and see what I can come up with.

Also, just looking at your circuit, the arrangement on the first timer doesn't look right. Usually an astable has 2 resistors R1 and R2 tied in series. Pin 7 usually goes to the junction of R1 and R2 while the combination of pin 2&6 got to the top of the capacitor. You might want to look into this. I have attached another file with this arrangement in it so you can take a look at that.

[lacy]

O.K I have 2 more circuit files for you to try. The first one manually interupts the sequence and the other uses a variation of the previous circuit to interupt the sequence after a time delay.

One note with both versions is that at start-up you have to manually reset the 4017 to zero. I don't know if this actually happens in a real circuit, but in my version of Multisim this IC comes up with a random LEDs lit until it is reset. This may not be necessary in a real circuit, but I don't know.

Here they are:

[GarretF]

Just a quick tip. You don't need to rename the file extension to ms9 to open the file in Multisim 9. Multisim 9 supports opening msm (Multisim 6) files, as do all versions from 6 to the latest.

Garret