Rising and Falling Edge triggered one-shot

> If you're squeamish add an even number of inverters between pin-5 of
> the 'HC74 and pin-2 of the'HC86.

Ugh.  I'd rather use up the unneeded three extra XOR gates in a (never seems to be smaller than 14 pins) XOR chip.  Are there no 8pin XOR chips anymore? Or even 6pin?  Ted

Den tirsdag den 16. januar 2018 kl. 00.44.10 UTC+1 skrev ted...@gmail.com:
> > If you're squeamish add an even number of inverters between pin-5 of
> > the 'HC74 and pin-2 of the'HC86.
> 
> Ugh.  I'd rather use up the unneeded three extra XOR gates in a (never seems to be smaller than 14 pins) XOR chip.  Are there no 8pin XOR chips anymore? Or even 6pin?  Ted

http://www.ti.com/lit/ds/symlink/sn74lvc1g86.pdf

> A simple approach is to use a FF to hold a state set by the MCU and the XOR 
> to detect edges on the incoming pulse.  The pulse edge rises, the XOR wakes 
> the CPU, the CPU changes the FF and the wakeup pulse ends.  In essence the 
> CPU becomes your delay element.

I like the idea.  No RC.  Just an XOR.  The CPU is powered exactly as long as it needs to be.  Should work for both edges.  I'll try it with some of those 'extra' XOR gates. :-)  Ted

On 2018-01-11 10:23, 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
>

Since price is so important you probably don't want a discrete solution 
with lots of parts because of the pick & place machine charges.

Consider an external watchdog timer (WDT) chip. Often they come in the 
same package with a power supply supervisor. They are cheap and used by 
people (like myself) who do not trust on-chip supervisor functions on 
micro controllers.

The way these work: Their output goes high for a certain time after 
either a rising or falling edge on the input signal. If no such 
transition occurs for a while their output goes low (meant to issue a 
micro controller reset) and this time would be your one-shot pulse 
length. You'd just have to pick one with the desired number of seconds. 
Some also have a voltage supervisor in there which keops the outut low 
until the supply is above a certain threshold. If you don't want that 
use one without or one with a low enough voltage threshold.

Another method is to take the cheapest micro controller you can find and 
program its internal timer so it will trigger a one-shot period after a 
"state change", thus after a falling as well as a rising edge.

-- 
Regards, Joerg

http://www.analogconsultants.com/

> http://www.ti.com/lit/ds/symlink/sn74lvc1g86.pdf

I'm drooling, but still stuck in the 'through hole' world just now until everything is proven.  I'm just basement entrepreneurial with an eye toward quantity in the future.  Surface mount is a challenge in development.  Gotta solder those little suckers on manually.  Ted

Den tirsdag den 16. januar 2018 kl. 01.22.28 UTC+1 skrev ted...@gmail.com:
> > http://www.ti.com/lit/ds/symlink/sn74lvc1g86.pdf
> 
> I'm drooling, but still stuck in the 'through hole' world just now until everything is proven.  I'm just basement entrepreneurial with an eye toward quantity in the future.  Surface mount is a challenge in development.  Gotta solder those little suckers on manually.  Ted

I find surface mount to be easier, no messing around with constantly flipping 
the board and trying to hold in parts before soldering, just align part and 
tack one pin and solder

On Mon, 15 Jan 2018 16:22:19 -0800 (PST), tedj121@gmail.com wrote:

>> http://www.ti.com/lit/ds/symlink/sn74lvc1g86.pdf
>
>I'm drooling, but still stuck in the 'through hole' world just now until everything is proven.  I'm just basement entrepreneurial with an eye toward quantity in the future.  Surface mount is a challenge in development.  Gotta solder those little suckers on manually.  Ted

There are a number of us who do prototype stuff with SMT parts.  John
Larkin has shown a lot of examples of the "dead bug" school of
prototyping.   You really should get the proper tools and leave
thru-hole behind.  You're really limiting yourself - thru-hole is
dead.

On 16/01/2018 00:51, krw@notreal.com wrote:
> On Mon, 15 Jan 2018 16:22:19 -0800 (PST), tedj121@gmail.com wrote:
> 
>>> http://www.ti.com/lit/ds/symlink/sn74lvc1g86.pdf
>>
>> I'm drooling, but still stuck in the 'through hole' world just now until everything is proven.  I'm just basement entrepreneurial with an eye toward quantity in the future.  Surface mount is a challenge in development.  Gotta solder those little suckers on manually.  Ted
> 
> There are a number of us who do prototype stuff with SMT parts.  John
> Larkin has shown a lot of examples of the "dead bug" school of
> prototyping.   You really should get the proper tools and leave
> thru-hole behind.  You're really limiting yourself - thru-hole is
> dead.

Through hole still lives where you want mechanical resilience for items 
like connectors. Otherwise I entirely agree.


-- 
Mike Perkins
Video Solutions Ltd
www.videosolutions.ltd.uk

On Tue, 16 Jan 2018 01:05:51 +0000, Mike Perkins <spam@spam.com>
wrote:

>On 16/01/2018 00:51, krw@notreal.com wrote:
>> On Mon, 15 Jan 2018 16:22:19 -0800 (PST), tedj121@gmail.com wrote:
>> 
>>>> http://www.ti.com/lit/ds/symlink/sn74lvc1g86.pdf
>>>
>>> I'm drooling, but still stuck in the 'through hole' world just now until everything is proven.  I'm just basement entrepreneurial with an eye toward quantity in the future.  Surface mount is a challenge in development.  Gotta solder those little suckers on manually.  Ted
>> 
>> There are a number of us who do prototype stuff with SMT parts.  John
>> Larkin has shown a lot of examples of the "dead bug" school of
>> prototyping.   You really should get the proper tools and leave
>> thru-hole behind.  You're really limiting yourself - thru-hole is
>> dead.
>
>Through hole still lives where you want mechanical resilience for items 
>like connectors. Otherwise I entirely agree.

Oh, certainly.  PTH capacitors may have lower ESL and ESR, as well. We
often use PTH capacitors, inductors, and of course, connectors.

tedj121@gmail.com wrote on 1/15/2018 7:01 PM:
>> A simple approach is to use a FF to hold a state set by the MCU and the XOR
>> to detect edges on the incoming pulse.  The pulse edge rises, the XOR wakes
>> the CPU, the CPU changes the FF and the wakeup pulse ends.  In essence the
>> CPU becomes your delay element.
>
> I like the idea.  No RC.  Just an XOR.  The CPU is powered exactly as long as it needs to be.  Should work for both edges.  I'll try it with some of those 'extra' XOR gates. :-)  Ted

Unless your MCU can remember and hold an output pin when powered down (not 
entirely unlikely) you will need some FF external to the MCU in addition to 
the XOR.

-- 

Rick C

Viewed the eclipse at Wintercrest Farms,
on the centerline of totality since 1998