555 monostable basics

Well, there is what is called a "retriggerable monostable" where subsequent pulses after the initial trigger (but before the output pulse completes) adds to the output pulse an additional pulse period that begins with that subsequent input trigger. In other words, many quick pulses yield one long output pulse that times out one output period after the last trigger.

There is also the case where the subsequent pulse does "reset" the output pulse to the quiescent state before it begins a new output pulse, often called a "restartable monostable." Many quick inputs yield many quick outputs the basic period pulse output after the last trigger.

A quick 'net search for either of those terms, plus "555," should turn up some candidates. There is also an inexpensive software app from Schematica that has wizards for these and many other 555 variations plus some handy aids for students/hobbyists/enthusiasts/new-guys. Look over at

Thanks for the replies. Yes interested - I've looked at several 555 design sites -not yet found one that covers this "condition". From your replies I see both possibilities are there with there with the 555 - an amazing piece of design that chip - no wonder its been around so long.

Look for for '555+missing pulse detector' to see a retriggerable configuration that does what you asked.

You could just breadboard it and see yourself. If you have no scope, do it with a long pulse so you can see the output with an LED.

Michael

On Wed, 12 Oct 2011 15:12:49 +0100, mike wrote:

--- OK.

Below is an LTspice circuit list that you can use to see (and edit, if you want to) the circuit schematic and run a simulation of the retriggerable 555 circuit.

If you don't have LTspice you can download it for free at:

what you'll need to do to run the sim is to copy the circuit list to a file and name it anything you like as long as it has a .asc extension, say, "555 retrigger.asc"

Then, once you've got LTspice installed and running, use it to navigate over to the file and left click on it.

You'll see the schematic fill the screen and, once it does, right click anywhere on the background, then left click on "RUN" in the menu box that pops up.

The sim will run, and when it's done you can probe around the schematic and left click on any node and see the waveform in the waveform viewer.

Enjoy!

Circuit list follows:

Version 4 SHEET 1 960 772 WIRE 224 144 -96 144 WIRE -192 208 -288 208 WIRE -96 208 -96 144 WIRE -96 208 -192 208 WIRE -64 208 -96 208 WIRE 256 208 160 208 WIRE -192 240 -192 208 WIRE -64 272 -96 272 WIRE 192 272 160 272 WIRE -96 336 -96 272 WIRE -64 336 -96 336 WIRE 320 336 160 336 WIRE 352 336 320 336 WIRE -192 368 -192 320 WIRE -96 368 -96 336 WIRE -96 368 -192 368 WIRE -192 400 -192 368 WIRE 224 400 224 144 WIRE 224 400 160 400 WIRE 320 464 320 336 WIRE -96 480 -96 368 WIRE 16 528 -32 528 WIRE 192 528 192 272 WIRE 192 528 96 528 WIRE -288 560 -288 208 WIRE 192 560 192 528 WIRE -288 688 -288 640 WIRE -192 688 -192 464 WIRE -192 688 -288 688 WIRE -96 688 -96 576 WIRE -96 688 -192 688 WIRE 192 688 192 640 WIRE 192 688 -96 688 WIRE 256 688 256 208 WIRE 256 688 192 688 WIRE 320 688 320 544 WIRE 320 688 256 688 WIRE -288 752 -288 688 FLAG -288 752 0 FLAG 352 336 OUT SYMBOL Misc\\NE555 48 304 M0 SYMATTR InstName U1 SYMBOL voltage 192 544 M0 WINDOW 3 24 104 Invisible 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 WINDOW 0 33 19 Left 2 SYMATTR Value PULSE(5 0 1 .1U .1U .1 .5 10) SYMATTR InstName V1 SYMBOL voltage -288 544 M0 WINDOW 123 0 0 Left 2 SYMATTR SpiceLine Rser=0 SYMATTR InstName V2 SYMATTR Value 5 SYMBOL res 336 448 M0 WINDOW 0 -42 36 Left 2 WINDOW 3 -57 70 Left 2 SYMATTR InstName R3 SYMATTR Value 1000 SYMBOL res -176 224 M0 SYMATTR InstName R1 SYMATTR Value 2meg SYMBOL cap -176 400 M0 SYMATTR InstName C1 SYMATTR Value 1µ SYMBOL pnp -32 576 R180 WINDOW 0 58 35 Left 2 WINDOW 3 52 64 Left 2 SYMATTR InstName Q1 SYMATTR Value 2N4403 SYMBOL res 0 512 M90 WINDOW 0 65 59 VBottom 2 WINDOW 3 68 59 VTop 2 SYMATTR InstName R2 SYMATTR Value 1000 TEXT -80 720 Right 2 !.tran 0 10s 0 .001s startup uic

-- JF

If It's being triggered by the Trigger input, no. It will complete the first initial cycle, how ever, you can force a reset of the time constant if you wish.

I am sure others are going to offer you a ton of options if that is what you need.

Jamie

Don't be so ridiculous. If you think working with a timer makes some one special, mainly you, then you are getting a little confused in life.

Intrude? I didn't ask for your opinion either. So who is doing the intruding? or should I say, instigating?

Is this forum just for you and yours cronies? Is there an initiation I must go through, rules set by yours truly?

If I knew you were some young hoodlum I would tell you to grow up how ever, I know that isn't the case and I find it surprising that you would behave in such a manner that would confuse others that didn't know you better, or maybe, we don't know you that well? Are you leading a multiple life there John? Have little friends you talk to upstairs?

Jesus john, go play your violin else where, I know far more than I need to know about working with a timer.

If the solutions offered were not satisfactory to the poster, I am sure many others here, including myself would of been more than happy to offer some other alternatives. But why waste bandwidth and time when you know people like you are just jumping at the bit to try and impress some one.

Jamie

Not a vanilla 555 circuit. A 74123 (or HC123) is retriggerable.

John

what a waste of bandspace and storage!

Jamie

--- So says the hypocrite loon who doesn't trim for relevance, but instead responds to 504 words with 7.

-- JF

Another waste of bandspace.

Jamie

Now you're catching on.

Too bad that you never will.