Forums

simple oneshot

Started by George Herold April 16, 2014
Hi all,  OK a silly basic question.
I'm doing some digital stuff.  
I wanted a one shot to reset some things, but didn't want to put in an entire chip
(74HC123.. or whatever the number is.)
So I just used a cap, resistor, diode and inverter.
https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG
Is this OK?  

Thanks,
George H.
On 04/16/2014 11:11 AM, George Herold wrote:
> Hi all, OK a silly basic question. > I'm doing some digital stuff. > I wanted a one shot to reset some things, but didn't want to put in an entire chip > (74HC123.. or whatever the number is.) > So I just used a cap, resistor, diode and inverter. > https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG > Is this OK? > > Thanks, > George H. >
The output rise time will be slow, due to the limited gain of the gate. Using a 74HC14 Schmitt inverter will help. It loads down its input very badly on falling edges, and the pulse width will be uncertain by about a factor of 2 due to the threshold voltage tolerance of the inverter. But for some jobs, a little M-squared-L is just the ticket. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
On Wednesday, April 16, 2014 12:56:49 PM UTC-4, Phil Hobbs wrote:
> On 04/16/2014 11:11 AM, George Herold wrote:
(weird I can see your reply but not my original post.. google groups is broken again... (yeah I know.))
> The output rise time will be slow, due to the limited gain of the gate. > Using a 74HC14 Schmitt inverter will help.
Check that's what I've got.
> > > It loads down its input very badly on falling edges, and the pulse width
Good point. I'll add another resistor in series with the cap. (say 1k in series an 10k to ground.) That will take care of my worries about the diode current too.
> will be uncertain by about a factor of 2 due to the threshold voltage > tolerance of the inverter.
Yeah no problem there... I've got plenty of time.
> > > But for some jobs, a little M-squared-L is just the ticket.
M-squared-L? what's that? A transformer? (googling brings up Mellissa's instagram site... I don't think that was your reference. :^)
>
George H.
> > > Cheers > > > > Phil Hobbs > > > > -- > > Dr Philip C D Hobbs > > Principal Consultant > > ElectroOptical Innovations LLC > > Optics, Electro-optics, Photonics, Analog Electronics > > > > 160 North State Road #203 > > Briarcliff Manor NY 10510 > > > > hobbs at electrooptical dot net > > http://electrooptical.net
On Wed, 16 Apr 2014 08:11:11 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

>Hi all, OK a silly basic question. >I'm doing some digital stuff. >I wanted a one shot to reset some things, but didn't want to put in an entire chip >(74HC123.. or whatever the number is.) >So I just used a cap, resistor, diode and inverter. >https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG >Is this OK? > >Thanks, >George H.
<http://www.analog-innovations.com/SED/GeorgeHeroldOneShot_2014_04_16.png> Leave D5 out if you don't mind symmetrical delay. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
On 04/16/2014 01:52 PM, George Herold wrote:
> On Wednesday, April 16, 2014 12:56:49 PM UTC-4, Phil Hobbs wrote: >> On 04/16/2014 11:11 AM, George Herold wrote: > (weird I can see your reply but not my original post.. > google groups is broken again... (yeah I know.)) > >> The output rise time will be slow, due to the limited gain of the gate. >> Using a 74HC14 Schmitt inverter will help. > Check that's what I've got. >> >> >> It loads down its input very badly on falling edges, and the pulse width > Good point. I'll add another resistor in series with the cap. (say 1k in series an 10k to ground.) That will take care of my worries about the diode current too. >> will be uncertain by about a factor of 2 due to the threshold voltage >> tolerance of the inverter. > Yeah no problem there... I've got plenty of time. >> >> >> But for some jobs, a little M-squared-L is just the ticket. > > M-squared-L? what's that? A transformer? > (googling brings up Mellissa's instagram site... I don't think that was your reference. :^) >> > George H.
Mickey Mouse Logic. (hat tip to Don Lancaster) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
In article <12536e91-630e-49ee-a04f-2b3b35b06974@googlegroups.com>, 
gherold@teachspin.com says...
> > Hi all, OK a silly basic question. > I'm doing some digital stuff. > I wanted a one shot to reset some things, but didn't want to put in an entire chip > (74HC123.. or whatever the number is.) > So I just used a cap, resistor, diode and inverter. > https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG > Is this OK? > > Thanks, > George H.
If you have two inverters you can put two in series and have a little hysteresis back to the first inverter via a R network to give you a nice fast snap. Of course, if you had a Schmitt inverter that would do the same for you , too. I am sure the common ones are more than quick enough. Or you can combine a PNP and NPN in a thyristor configuration which will not hold latch but will snap very quickly and give you hysteresis. Or, you could employ a 555 and just do a one shot there. But in that case, you could simply open the digikey or mouser book and get a power management chip. Jamie
On Wednesday, April 16, 2014 2:27:59 PM UTC-4, Jim Thompson wrote:
> On Wed, 16 Apr 2014 08:11:11 -0700 (PDT), George Herold > > >https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG > > > <http://www.analog-innovations.com/SED/GeorgeHeroldOneShot_2014_04_16.png> > > > Leave D5 out if you don't mind symmetrical delay.
Thanks Jim... I'll have to look at that a bit more. Is this going to give me a delay or a one shot at the edge? (At the moment I just want a one shot...) George H.
> > > > ...Jim Thompson > > -- > > | James E.Thompson | mens | > > | Analog Innovations | et | > > | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | > > | San Tan Valley, AZ 85142 Skype: Contacts Only | | > > | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | > > | E-mail Icon at http://www.analog-innovations.com | 1962 | > > > > I love to cook with wine. Sometimes I even put it in the food.
On Wednesday, April 16, 2014 5:36:44 PM UTC-4, Maynard A. Philbrook Jr. wrote:
> In article <12536e91-630e-49ee-a04f-2b3b35b06974@googlegroups.com>, > > gherold@teachspin.com says... > > > > > > Hi all, OK a silly basic question. > > > I'm doing some digital stuff. > > > I wanted a one shot to reset some things, but didn't want to put in an entire chip > > > (74HC123.. or whatever the number is.) > > > So I just used a cap, resistor, diode and inverter. > > > https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG > > > Is this OK? > > > > > > Thanks, > > > George H. > > > > If you have two inverters you can put two in series and have a little > > hysteresis back to the first inverter via a R network to give you a nice > > fast snap. > > > > Of course, if you had a Schmitt inverter that would do the same for you > > , too. I am sure the common ones are more than quick enough. > > > > Or you can combine a PNP and NPN in a thyristor configuration which > > will not hold latch but will snap very quickly and give you hysteresis. > > > > Or, you could employ a 555 and just do a one shot there. But in that > > case, you could simply open the digikey or mouser book and get a power > > management chip. > > > > Jamie
Thanks Jamie, What i've got looks very simple. Two R's, a C and Diode. George H.
On Wednesday, April 16, 2014 4:24:27 PM UTC-4, Phil Hobbs wrote:

> > Mickey Mouse Logic. (hat tip to Don Lancaster) >
Got it. (That doesn't sound very good at the design review though.) Does Don do stuff like this in his CMOS cookbook. (I've never read any of Don's books. I thought it would be obsolete, but it looks to still be selling well on amazon. George h.
> > Cheers > > > > Phil Hobbs > > > > > > -- > > Dr Philip C D Hobbs > > Principal Consultant > > ElectroOptical Innovations LLC > > Optics, Electro-optics, Photonics, Analog Electronics > > > > 160 North State Road #203 > > Briarcliff Manor NY 10510 > > > > hobbs at electrooptical dot net > > http://electrooptical.net
On Thu, 17 Apr 2014 10:32:26 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

>On Wednesday, April 16, 2014 2:27:59 PM UTC-4, Jim Thompson wrote: >> On Wed, 16 Apr 2014 08:11:11 -0700 (PDT), George Herold >> >> >https://www.dropbox.com/s/flnonc9rgwmerhw/DSCF0082.JPG >> >> >> <http://www.analog-innovations.com/SED/GeorgeHeroldOneShot_2014_04_16.png> >> >> >> Leave D5 out if you don't mind symmetrical delay. >Thanks Jim... I'll have to look at that a bit more. >Is this going to give me a delay or a one shot at the edge? >(At the moment I just want a one shot...) > >George H. >> >>
[snip] It's a delay block, but should serve your purpose as a delayed reset. I use that architecture in a lot of my chip designs because, without ESD, it's a pretty stable delay, independent of VDD, pretty much just the RC time constant for delays much longer than the inherent inverter delay. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.