Create a long pulse

[George Sephton]

Hi,
I need to create a pulse of about half a second from an electrical signal, so that even if there is an electrical signal being passed for an hour until it stops only a half-second electrical pulse is outputted. I need to do this without the use of a PICAXE as I've run out of output ports and my knowledge of capacitors isn't that great.
Thanks,
George S.

 

[jglenn]

You can trigger a 555 timer from a low going signal, use a capacitor differentiator as an edge detector. I can draw a picture if I know the nature of the trigger signal. Is it low going? 0-5V? If you have any invertors in the circuit, like the 4584, you can do it with R, C, sometimes diodes. Not hard.

 

[womai]

On the other hand, once you are ready to use a 555 (= 8-pin DIP package plus a few discrete components), you could also use a Picaxe 08M (8-pin DIP package plus a few discrete components) (and who knows what those additional pins on the Picaxe could be used for!)

Wolfgang

 

[manuka]

as I've run out of output ports

Is this on a 08M ? You may as well keep everything PICAXEd, so consider the extra ports offerered by a 14M, 20M or maybe the new 18M ? Stan

 

[George Sephton]

I could use a PICAXE but really I don't have that many availible and i'd like to run it analogue with a 555 timer circuit. What happens is I have a button debounced to a decade counter so each click has only 3 steps: 2,1,Go. Each step lights and LED and on go there will be a link conncted to a keyboard circuit which will "press" spacebar. However the go light won't go off immediately and may stay there for about 20 miutes until realesed which isn't good as the keyboard will have sat and made a billion spaces, not good.
It won't be anymore than 5V but if you could show me the circuit that'd be great!
Thanks,
George S.

 

[SilentScreamer]

I could use a PICAXE but really I don't have that many availible and i'd like to run it analogue with a 555 timer circuit. What happens is I have a button debounced to a decade counter so each click has only 3 steps: 2,1,Go. Each step lights and LED and on go there will be a link conncted to a keyboard circuit which will "press" spacebar. However the go light won't go off immediately and may stay there for about 20 miutes until realesed which isn't good as the keyboard will have sat and made a billion spaces, not good.
It won't be anymore than 5V but if you could show me the circuit that'd be great!
Thanks,
George S.

(Assuming this is for a actual computer and your not just using a keyboard and the operating system is windows, I can't comment for macs or linux)

You could just disable repeated keys in control pannel.

 

[George Sephton]

that's really an easy way out but although that is a possibility I need to make sure there is an electrical signal for a short time.

 

[fernando_g]

Check this out

http://www.instructables.com/id/SEFZK1SFC2BTKRR/