how to generate a single pulse from a switch closure

Guest
if I close a switch (non momentary) how can I trigger a 555 by
generating a single pulse?

example: relay contacts close, debounce the closure, generate a pulse
triggering a 555.
 
On Fri, 16 Jan 2009 05:29:16 -0800 (PST), jimsipt@gmail.com wrote:

if I close a switch (non momentary) how can I trigger a 555 by
generating a single pulse?

example: relay contacts close, debounce the closure, generate a pulse
triggering a 555.
Click to expand...
Basically, by with a capacitor on the trigger input so that the 555 is
sensitive to edges, not levels. Google for "555 edge trigger" for
examples.

There are software packages (e.g.,
<http://www.schematica.com/555_Timer_design/555_Timer_PRO.htm>) that
could help as well.

--
Rich Webb Norfolk, VA
 
On Fri, 16 Jan 2009 05:29:16 -0800 (PST), jimsipt@gmail.com wrote:

if I close a switch (non momentary) how can I trigger a 555 by
generating a single pulse?

example: relay contacts close, debounce the closure, generate a pulse
triggering a 555.
Click to expand...

v+---------100k-------+------switch------+-------to 555
| |
| |
| |
0.1 uF 1K
| |
| |
| |
| |
gnd gnd

John
 
On Fri, 16 Jan 2009 08:42:44 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 16 Jan 2009 05:29:16 -0800 (PST), jimsipt@gmail.com wrote:

if I close a switch (non momentary) how can I trigger a 555 by
generating a single pulse?

example: relay contacts close, debounce the closure, generate a pulse
triggering a 555.


v+---------100k-------+------switch------+-------to 555
| |
| |
| |
0.1 uF 1K
| |
| |
| |
| |
gnd gnd

John
Click to expand...

And if you have an SPDT switch, it can be even simpler.

With a hazard.

John
 
On Fri, 16 Jan 2009 08:42:44 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 16 Jan 2009 05:29:16 -0800 (PST), jimsipt@gmail.com wrote:

if I close a switch (non momentary) how can I trigger a 555 by
generating a single pulse?

example: relay contacts close, debounce the closure, generate a pulse
triggering a 555.


v+---------100k-------+------switch------+-------to 555
| |
| |
| |
0.1 uF 1K
| |
| |
| |
| |
gnd gnd
Click to expand...

And that pulse is going to which pin on the 555?

JF
 
On Fri, 16 Jan 2009 08:42:44 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 16 Jan 2009 05:29:16 -0800 (PST), jimsipt@gmail.com wrote:

if I close a switch (non momentary) how can I trigger a 555 by
generating a single pulse?

example: relay contacts close, debounce the closure, generate a pulse
triggering a 555.


v+---------100k-------+------switch------+-------to 555
| |
| |
| |
0.1 uF 1K
| |
| |
| |
| |
gnd gnd
Click to expand...
---
Don't you mean:


gnd---------100k------+------switch------+-------to 555 pin 2
| |
| |
| |
0.1 uF 1K
| |
| |
| |
| |
+v +v

?

Version 4
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TEXT -72 280 Left 0 !.model SW SW(Ron=1 Roff=10Meg Vt=0.5Vh=0)
TEXT -114 360 Left 0 !.tran 5


JF
 
On Fri, 16 Jan 2009 13:28:52 -0600, John Fields
<jfields@austininstruments.com> wrote:

On Fri, 16 Jan 2009 08:42:44 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 16 Jan 2009 05:29:16 -0800 (PST), jimsipt@gmail.com wrote:

if I close a switch (non momentary) how can I trigger a 555 by
generating a single pulse?

example: relay contacts close, debounce the closure, generate a pulse
triggering a 555.


v+---------100k-------+------switch------+-------to 555
| |
| |
| |
0.1 uF 1K
| |
| |
| |
| |
gnd gnd

---
Don't you mean:


gnd---------100k------+------switch------+-------to 555 pin 2
| |
| |
| |
0.1 uF 1K
| |
| |
| |
| |
+v +v

?
Click to expand...
Does a 555 need a negative trigger pulse? I never knew that.

You're the 555 expert.

John
 
On Fri, 16 Jan 2009 21:07:24 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 16 Jan 2009 13:28:52 -0600, John Fields
jfields@austininstruments.com> wrote:

On Fri, 16 Jan 2009 08:42:44 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 16 Jan 2009 05:29:16 -0800 (PST), jimsipt@gmail.com wrote:

if I close a switch (non momentary) how can I trigger a 555 by
generating a single pulse?

example: relay contacts close, debounce the closure, generate a pulse
triggering a 555.


v+---------100k-------+------switch------+-------to 555
| |
| |
| |
0.1 uF 1K
| |
| |
| |
| |
gnd gnd

---
Don't you mean:


gnd---------100k------+------switch------+-------to 555 pin 2
| |
| |
| |
0.1 uF 1K
| |
| |
| |
| |
+v +v

?


Does a 555 need a negative trigger pulse?
Click to expand...
---
Normally, yes.

However, by tying the THRESHOLD input high and using your
positive-pulse-out debouncer, the 555 will act like an inverter and
output a negative-going pulse, lasting for about the RC of your
debouncer, which can be used to trigger a downstream 555.
---

I never knew that.
Click to expand...
---
You're welcome. :)
---

You're the 555 expert.
Click to expand...
---
Thanks a lot, Mr. Snide.

JF
 
John Larkin wrote:
On Fri, 16 Jan 2009 13:28:52 -0600, John Fields
jfields@austininstruments.com> wrote:


On Fri, 16 Jan 2009 08:42:44 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:


On Fri, 16 Jan 2009 05:29:16 -0800 (PST), jimsipt@gmail.com wrote:


if I close a switch (non momentary) how can I trigger a 555 by
generating a single pulse?

example: relay contacts close, debounce the closure, generate a pulse
triggering a 555.


v+---------100k-------+------switch------+-------to 555
| |
| |
| |
0.1 uF 1K
| |
| |
| |
| |
gnd gnd

---
Don't you mean:


gnd---------100k------+------switch------+-------to 555 pin 2
| |
| |
| |
0.1 uF 1K
| |
| |
| |
| |
+v +v

?



Does a 555 need a negative trigger pulse? I never knew that.

You're the 555 expert.

John



Yes it does.
Click to expand...
Trigger is a PNP and threshold a NPN.


http://webpages.charter.net/jamie_5"
 
On Sat, 17 Jan 2009 18:03:27 -0500, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

John Larkin wrote:
On Fri, 16 Jan 2009 13:28:52 -0600, John Fields
jfields@austininstruments.com> wrote:


On Fri, 16 Jan 2009 08:42:44 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:


On Fri, 16 Jan 2009 05:29:16 -0800 (PST), jimsipt@gmail.com wrote:


if I close a switch (non momentary) how can I trigger a 555 by
generating a single pulse?

example: relay contacts close, debounce the closure, generate a pulse
triggering a 555.


v+---------100k-------+------switch------+-------to 555
| |
| |
| |
0.1 uF 1K
| |
| |
| |
| |
gnd gnd

---
Don't you mean:


gnd---------100k------+------switch------+-------to 555 pin 2
| |
| |
| |
0.1 uF 1K
| |
| |
| |
| |
+v +v

?



Does a 555 need a negative trigger pulse? I never knew that.

You're the 555 expert.

John



Yes it does.
Trigger is a PNP and threshold a NPN.


http://webpages.charter.net/jamie_5"
Click to expand...
Oh. I only used a 555 once, free-running, to charge-pump some +12 into
-10 or some such. I took the RC feedback from the output pin, instead
of all that complicated charge-discharge stuff, which seemed more
obvious than the multi-resistor stuff on the data sheet.

But that was a long time ago, and I doubt I'll ever use one again.

John
 
John Larkin wrote in message ...
On Sat, 17 Jan 2009 18:03:27 -0500, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

John Larkin wrote:
On Fri, 16 Jan 2009 13:28:52 -0600, John Fields
jfields@austininstruments.com> wrote:


On Fri, 16 Jan 2009 08:42:44 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:


On Fri, 16 Jan 2009 05:29:16 -0800 (PST), jimsipt@gmail.com wrote:


if I close a switch (non momentary) how can I trigger a 555 by
generating a single pulse?

example: relay contacts close, debounce the closure, generate a pulse
triggering a 555.


v+---------100k-------+------switch------+-------to 555
| |
| |
| |
0.1 uF 1K
| |
| |
| |
| |
gnd gnd

---
Don't you mean:


gnd---------100k------+------switch------+-------to 555 pin 2
| |
| |
| |
0.1 uF 1K
| |
| |
| |
| |
+v +v

?



Does a 555 need a negative trigger pulse? I never knew that.

You're the 555 expert.

John



Yes it does.
Trigger is a PNP and threshold a NPN.


http://webpages.charter.net/jamie_5"

Oh. I only used a 555 once, free-running, to charge-pump some +12 into
-10 or some such. I took the RC feedback from the output pin, instead
of all that complicated charge-discharge stuff, which seemed more
obvious than the multi-resistor stuff on the data sheet.

But that was a long time ago, and I doubt I'll ever use one again.

John
Click to expand...
If you hold pin2 low, the output goes high and stays there. It won't time
out. Pin 2 has to be ac coupled.
bg
 
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