Rising and Falling Edge triggered one-shot

Started by January 11, 2018
Hi,

I'd like to take a long input pulse and trigger a much shorter one-shot pulse at its
rising and falling edges.  Ideally, only a single input should be required (i.e. the
one long pulse) for minimal part count.  I've looked over several timer ics and none
seem to fit the bill or are too pricey like the 6993s.  Can anyone suggest an
appropriate ic?  I would think it a common enough function to warrant a dedicated
chip.  Thanks,  Ted
On 01/11/2018 01:23 PM, tedj121@gmail.com wrote:
> Hi, > > I'd like to take a long input pulse and trigger a much shorter > one-shot pulse at its rising and falling edges. Ideally, only a > single input should be required (i.e. the one long pulse) for minimal > part count. I've looked over several timer ics and none seem to fit > the bill or are too pricey like the 6993s. Can anyone suggest an > appropriate ic? I would think it a common enough function to warrant > a dedicated chip. Thanks, Ted >
How long is long, how short is short, and what supply voltage do you plan to use? Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net https://hobbs-eo.com
On 11/01/2018 18:23, tedj121@gmail.com wrote:
> Hi, > > I'd like to take a long input pulse and trigger a much shorter > one-shot pulse at its rising and falling edges. Ideally, only a > single input should be required (i.e. the one long pulse) for minimal > part count. I've looked over several timer ics and none seem to fit > the bill or are too pricey like the 6993s. Can anyone suggest an > appropriate ic? I would think it a common enough function to warrant > a dedicated chip. Thanks, Ted
How short is much shorter? XOR against a delayed copy of itself? -- Regards, Martin Brown
On Thu, 11 Jan 2018 18:37:33 +0000, Martin Brown
<'''newspam'''@nezumi.demon.co.uk> wrote:

>On 11/01/2018 18:23, tedj121@gmail.com wrote: >> Hi, >> >> I'd like to take a long input pulse and trigger a much shorter >> one-shot pulse at its rising and falling edges. Ideally, only a >> single input should be required (i.e. the one long pulse) for minimal >> part count. I've looked over several timer ics and none seem to fit >> the bill or are too pricey like the 6993s. Can anyone suggest an >> appropriate ic? I would think it a common enough function to warrant >> a dedicated chip. Thanks, Ted > >How short is much shorter? XOR against a delayed copy of itself?
That's the classic. An RC, or a string of gates, can do the delay. Or even a PCB trace! -- John Larkin Highland Technology, Inc picosecond timing precision measurement jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
Hi and thanks for responding.

I have a touch sensor.  Goes on when touched and off when not.  I want my uC to do a
service operation at each edge of that (possibly long) 'pulse'.  My uC needs about a
second or so from power up to the beginning of program start.  The uC is energized
by that sensor signal being ON, at which point it immediately asserts another bit
that controls whether to continue power to itself and other circuits.  So the
one-shot duration is just long enough to wake up the uC, which then services the
event and then goes back to sleep.

I plan to use a four cell (or possibly six) penlight pack for power.  I'm hoping to
tolerate battery decay to just above 3.3 volts from a max of about 6 or 9.

So the one-shots are about a second or so in duration and the spacing between the
sensor signal edges is typically several seconds.  Most one-shots I've found assume
a trigger pulse much shorter than the one-shot itself and I need the reverse.  An
input that initiates an identical pulse at either edge would be ideal.

Price is a consideration - a cheap timer and few external components is a plus.

I want to implement a sleep mode whose quiescent current only powers the touch
sensor (at ~ 5nA) to maximize battery life with all else being off.

Thanks, Ted

On Thursday, January 11, 2018 at 1:23:18 PM UTC-5, ted...@gmail.com wrote:
> Hi, > > I'd like to take a long input pulse and trigger a much shorter one-shot pulse at
its rising and falling edges. Ideally, only a single input should be required (i.e. the one long pulse) for minimal part count. I've looked over several timer ics and none seem to fit the bill or are too pricey like the 6993s. Can anyone suggest an appropriate ic? I would think it a common enough function to warrant a dedicated chip. Thanks, Ted
Hi and thanks for responding. 

I have a touch sensor.  Goes on when touched and off when not.  I want my uC to do a
service operation at each edge of that (possibly long) 'pulse'.  My uC needs about a
second or so from power up to the beginning of program start.  The uC is energized
by that sensor signal being ON.  At program start it immediately asserts another bit
that controls whether to continue power to itself and other circuits.  So the
one-shot duration is just long enough to wake up the uC, which then services the
event and then goes back to sleep. 

I plan to use a four cell (or possibly six) penlight pack for power.  I'm hoping to
tolerate battery decay to just above 3.3 volts from a max of about 6 or 9. 

So the one-shots are about a second or so in duration and the spacing between the
sensor signal edges is typically several seconds.  Most one-shots I've found assume
a trigger pulse much shorter than the one-shot itself and I need the reverse.  An
input that initiates an identical pulse at either edge would be ideal. 

Price is a consideration - a cheap timer and few external components is a plus. 

I want to implement a sleep mode whose quiescent current only powers the touch
sensor (at ~ 5nA) to maximize battery life with all else being off. 

Thanks, Ted 

On Thursday, January 11, 2018 at 1:23:18 PM UTC-5, ted...@gmail.com wrote: 
> Hi, > > I'd like to take a long input pulse and trigger a much shorter one-shot pulse at
its rising and falling edges. Ideally, only a single input should be required (i.e. the one long pulse) for minimal part count. I've looked over several timer ics and none seem to fit the bill or are too pricey like the 6993s. Can anyone suggest an appropriate ic? I would think it a common enough function to warrant a dedicated chip. Thanks, Ted
Chips like:

CD4538 - https://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/CD4538BC.pdf
74123 - http://www.ti.com/lit/ds/symlink/sn74lvc1g123.pdf
TPL5110 - file:///C:/Backup/Android/Feeder/tpl5110.pdf

seem promising, but I'd like to spice test whether any can do the job but can find
no models.  Hoping I might happen upon a guru.

Could only find: 
HC4538_JT.zip - http://www.analog-innovations.com/subcircuits.html
but it doesn't appear to work.
Chips like:

CD4538 - https://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/CD4538BC.pdf
74123 - http://www.ti.com/lit/ds/symlink/sn74lvc1g123.pdf
TPL5110 - http://www.ti.com/lit/ds/symlink/tpl5110.pdf

seem promising, but I'd like to spice test whether any can do the job but can find
no models.  Hoping I might happen upon a guru.

Could only find: 
HC4538_JT.zip - http://www.analog-innovations.com/subcircuits.html
but it doesn't appear to work.

On 1/11/2018 12:57 PM, tedj121@gmail.com wrote:
> Hi and thanks for responding. > > I have a touch sensor. Goes on when touched and off when not. I want my uC to do
a service operation at each edge of that (possibly long) 'pulse'. My uC needs about a second or so from power up to the beginning of program start. The uC is energized by that sensor signal being ON. At program start it immediately asserts another bit that controls whether to continue power to itself and other circuits. So the one-shot duration is just long enough to wake up the uC, which then services the event and then goes back to sleep.
> > I plan to use a four cell (or possibly six) penlight pack for power. I'm hoping
to tolerate battery decay to just above 3.3 volts from a max of about 6 or 9.
> > So the one-shots are about a second or so in duration and the spacing between the
sensor signal edges is typically several seconds. Most one-shots I've found assume a trigger pulse much shorter than the one-shot itself and I need the reverse. An input that initiates an identical pulse at either edge would be ideal.
> > Price is a consideration - a cheap timer and few external components is a plus. > > I want to implement a sleep mode whose quiescent current only powers the touch
sensor (at ~ 5nA) to maximize battery life with all else being off.
> > Thanks, Ted > > On Thursday, January 11, 2018 at 1:23:18 PM UTC-5, ted...@gmail.com wrote: >> Hi, >> >> I'd like to take a long input pulse and trigger a much shorter one-shot pulse at
its rising and falling edges. Ideally, only a single input should be required (i.e. the one long pulse) for minimal part count. I've looked over several timer ics and none seem to fit the bill or are too pricey like the 6993s. Can anyone suggest an appropriate ic? I would think it a common enough function to warrant a dedicated chip. Thanks, Ted
>
interrupt on pin change?
Hi Mike, 

> interrupt on pin change?
I think that would require my Bluetooth Bee Standalone v1 (the uC) to remain energized to catch the interrupt, so that would not work. I could simply keep the uC on while the touch sensor is on, but I'd rather not consume current when the uC is not needed for service (i.e. the bulk of the long pulse).