Re: Separate pulses from edges?

"John O'Flaherty" <quiasmox@xxxxxxxxx> wrote:


Terry Pinnell wrote:
"John O'Flaherty" <quiasmox@xxxxxxxxx> wrote:


Terry Pinnell wrote:
Terry Pinnell <terrypinDELETE@xxxxxxxxxxxxxxxxxxx> wrote:

I have a long, clean positive pulse (hours in duration). How can I get
two *separate* 10 ms +ve pulses from the leading and trailing edges
please?

A simple RC differentiator (of appropriate polarity) would be the
obvious solution if I only wanted one or the other. But I can't figure
out how to get *both*, as separate signals.

FWIW, I want to take these pulses to the Set and Reset pins of a 4013.

Thanks guys, much appreciate all the replies. Some neat ideas to
follow up there.

But even while composing my OP it was nagging away at me that I'd
asked essentially the same question before. Further digging this
morning turned it up:
news:f71621tpfvur92en3q138qdlkjk12ioca3@xxxxxxx
Subject: 2 pulses from 1
Date: Mon, 28 Feb 2005

Premature senility aside, I'm guessing that the reason it had slipped
my mind was that, although I had two great solutions from Fred Bartoli
and Fred Bloggs, I'd managed to come up with something trivially
simple myself that seemed to do the job. In fact, then and now, I'd
ignored the obvious: simply invert one of the inputs and use a vanilla
RC differentiator on each.

This was the circuit I used then.
http://www.terrypin.dial.pipex.com/Images/CurtainTimerAddOn.gif

I'm pretty sure that was what I implemented, and the gadget has been
working OK in the 16 months or so since.

The key difference *this* time is that I hope to feed these +ve pulses
(or squared up versions of them) not to a 4001 bistable but to a 4013,
as mentioned.

I haven't got around to that stage yet, so would welcome any feedback
- especially if my idea is a non-starter. I want the 4013 to achieve
the following 3 things:

1. +ve pulse A to Set pin 8 always sets or keeps 4013 output high.

2. +ve pulse B to Reset pin 10 always resets or keeps 4013 output low.

3. A +ve pulse T (from another source) to Clock pin 3 always toggles
the 4013 output.

For background, the practical application is a garden lights
controller for my son. At present the lights have an on/off switch
inconveniently located in his shed/garage at the bottom of the rear
garden. My unit should
- Switch (or keep) the lights on at dusk
- Switch (or keep) the lights off at dawn
- Toggle the lights on or off at any time from a radio signal from the
house, improvised from a wireless doorbell adapter.

Now I see why you wanted those signals to go into the set/reset inputs
of a toggle flip-flop. This being your target, you might use John
Popelish's idea of a single time constant with an xor gate to get both
change signals on a single line. These could be used to reset an R/S
flip-flop. The set for that flip-flop would be your radio signal, and
the output of that flip-flop would go to another xor in the package to
reverse the current sense of the lights. That is, the radio signal
would turn the lights off if they would otherwise be on, on if they
would be off. Either normal day/night transition would reset the
sense-reversing flip-flop. The advantage of doing it this way is using
only a single time constant, with both signals on one line, and using a
single pair of gates for the R-S flip flop.

Thanks John, but I don't see how that could work. John Fields pointed
out the basic flaw over the source signals in his reply to John
Popelish up-thread,

There also seems another problem to me. In your follow-up to JF, you
say "That RS latch is one input to an xor gate, whose other input is
just the day/night condition. The output of that xor gate is
transmitted to the light control."

But surely the XOR's output would depend on the current state of the
RS latch? For example, if the latch had been set low during the night
(maybe my son had switched off the lights before going to bed), then
at dawn they would go back *on* again.

Yes, that's the point of the latch- it toggles the output of your
circuit away from its normal state (by using the output xor as a
switchable inverter), and then the whole thing goes back to its normal
state at each transition from night to day. I just posted a jpg
schematic on a.b.s.e. Just to be sure, I whipped up a quick breadboard,
and it seems to do what you want rather simply. Again, unless I'm still
misunderstanding. :-)

I think you now agree?

--
Terry Pinnell
Hobbyist, West Sussex, UK
.

Relevant Pages

  • Re: Separate pulses from edges?
    ... I want to take these pulses to the Set and Reset pins of a 4013. ... the practical application is a garden lights ... Now I see why you wanted those signals to go into the set/reset inputs ... Popelish's idea of a single time constant with an xor gate to get both ...
    (sci.electronics.design)
  • Re: Separate pulses from edges?
    ... I want to take these pulses to the Set and Reset pins of a 4013. ... the practical application is a garden lights ... Now I see why you wanted those signals to go into the set/reset inputs ... of a toggle flip-flop. ...
    (sci.electronics.design)
  • Re: Separate pulses from edges?
    ... I want to take these pulses to the Set and Reset pins of a 4013. ... the practical application is a garden lights ... Now I see why you wanted those signals to go into the set/reset inputs ... of a toggle flip-flop. ...
    (sci.electronics.design)
  • Re: Separate pulses from edges?
    ... I want to take these pulses to the Set and Reset pins of a 4013. ... the practical application is a garden lights ... Now I see why you wanted those signals to go into the set/reset inputs ... This being your target, you might use John ...
    (sci.electronics.design)
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