sustain or latch a control signal ?

[harps]

hello .not sure if this will make sense, but here goes:

i am wondering if there is a simple solution for holding/sustaining a 5volt trigger signal? for example: a control voltage of 5v+ might be input into a circuit but only be sent for a short time, maybe just a 10ms hold time before it cuts out.

One way to sustain or hold that trigger could be through latch relay, but a mechanical latch relay takes time to latch on,so i wonder, is there by chance a circuit that can hold/sustain a 5v volt control signal? Maybe a capacitor and resistor combination ? with a variable resistor to vary the time the latch holds for?

i am trying to build a little circuit that listens out for a control signal and turns on a light and also turn on various other circuits via fast srr relay, but my control signal is only present for a short time ( to short a time), i really need the signal to hold/sustain and be ultra fast in its response, so a mechanical latch would be to slow (3 ms or more) where as, a transistor/capacitor type circuit can respond within a few nano seconds. I thought there might be a common type of circuit to deal with this type of problem?

maybe a timer ? So that when the control signal is sent the timer instantly outputs a 5volt signal for the desired length of time ( using a variable resistor or changing the size of a capacitor?)

hope this all makes sense thanks for any help : )

 

[Dx3]

There is a 555 timer circuit called a pulse stretcher or a one-shot, or maybe it's called a monostable multivibrator. Anyway, pulse goes in, pulse comes out and comes out and comes out.

Look up those names I gave you.

 

[harps]

hey cool i have a 555 timer somewhere ! thanks for the info.

 

[Dx3]

this is a link to an educational page on this thing you want.

 

[harps]

hello

i found this amazing webpage that shows a monostable multivibrator in action , you can see how it works , you click the H input and it outputs for a short while you can even edit the capacitor and resistors to a greater value.which extends the length of time the output is on.

its great try this out : 555 Monostable Multivibrator

only thing is the multivibrator only goes on when the control input is low. i think i might have a way around via a "not gate" on the input , i shall give it a try

thanks all.

 

[Dx3]

It's pretty normal to have to do an "invert" on the output or the input.
I am attaching a "new, improved" dual 555. It is more convenient, but almost nobody has a few in their work bench drawer.

It's just more education.

 

[harps]

hello : )

luckly i have a pack of 10 NE555 timers , tonight i tried lots of circuit variations found on wiki and other sources but i think i might be blowing my 555 chips? ( they might be a sensitive version:?)

i was using 5v from a regulator for the VCC and the trig input also.

the data sheet says from what i gather, with a vcc of 5v the max trig input is 2.2v typical 1.6v
heres a link to the data sheet :
**broken link removed**

V
Vtrig----------------min-typ-max-min-typ- max
-----VCC = +15V--4.5--5.....5.2-4.5-5-----5.6
-----VCC = +5V---1.45-1.67-1.9-1.1-1.67-2.2

so i think when i try again tomorrow i need to add a large resistor between the regulator and the trig input.?

i might even need to add resistors to the thresh input too? darn it, wish i had a normal 555 timer rather than the "NE" version

 

[Dx3]

NE is a normal version. The trigger and threshold are listening ports. They are not harmed by voltages between ground and Vcc. One problem is that if you apply Vcc directly to the trigger, it will always believe it is high and the chip won't oscillate or time anything.

 

[harps]

hi,

should i use an alternative psu for the trigger? another regulator perhaps or a battery? if the vcc i use is from a 5v
regulator , how about if i use a 2.5 v regulator for the trig?

thanks for your help : )

 

[Dx3]

No. Why would you try to disable the trigger with an outside source? You have everything you need right there between 0 and 5 volts.

 

[harps]

i fixed it i am not sure why? but its just stated working. lol, its 4am now , how time flies . : )

thanks.

 

[Dx3]

Please sleep. You are starting to sound confused.