Forums

super simple pulse stretcher

Started by bitrex June 20, 2015
I have a need to take a square pulse of 0V/+5V and about 5-10ms 
duration, and stretch it out long enough to flash a LED brightly enough 
to be visible indoors under "ordinary" lighting conditions.

I currently only have op-amps on the board and would rather not add any 
logic ICs to do this.  So using low-speed op amps and discretes would be 
fine.  The pulse source into the stretcher would be low impedance.

An optional feature would be to have the "stretch" duration decrease the 
more rapidly pulses are coming into the circuit.  But that is not a 
requirement if it needs significant complexity.
On 6/20/2015 8:08 AM, bitrex wrote:
> I have a need to take a square pulse of 0V/+5V and about 5-10ms > duration, and stretch it out long enough to flash a LED brightly enough > to be visible indoors under "ordinary" lighting conditions. > > I currently only have op-amps on the board and would rather not add any > logic ICs to do this. So using low-speed op amps and discretes would be > fine. The pulse source into the stretcher would be low impedance. > > An optional feature would be to have the "stretch" duration decrease the > more rapidly pulses are coming into the circuit. But that is not a > requirement if it needs significant complexity.
What's wrong with a 5-10ms flash? I'm flashing some at 400us and they are easily visible in my shop with florescent lighting.
On Sat, 20 Jun 2015 09:08:31 -0400, bitrex
<bitrex@de.lete.earthlink.net> wrote:

>I have a need to take a square pulse of 0V/+5V and about 5-10ms >duration, and stretch it out long enough to flash a LED brightly enough >to be visible indoors under "ordinary" lighting conditions. > >I currently only have op-amps on the board and would rather not add any >logic ICs to do this. So using low-speed op amps and discretes would be >fine. The pulse source into the stretcher would be low impedance. > >An optional feature would be to have the "stretch" duration decrease the >more rapidly pulses are coming into the circuit. But that is not a >requirement if it needs significant complexity.
NPN emitter follower driving R-C to ground, then a comparator. Use an opamp as the comparator. -- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Sat, 20 Jun 2015 09:08:31 -0400, bitrex
<bitrex@de.lete.earthlink.net> wrote:

>I have a need to take a square pulse of 0V/+5V and about 5-10ms >duration, and stretch it out long enough to flash a LED brightly enough >to be visible indoors under "ordinary" lighting conditions. > >I currently only have op-amps on the board and would rather not add any >logic ICs to do this. So using low-speed op amps and discretes would be >fine. The pulse source into the stretcher would be low impedance. > >An optional feature would be to have the "stretch" duration decrease the >more rapidly pulses are coming into the circuit. But that is not a >requirement if it needs significant complexity.
Supplies? ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | 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 6/20/2015 11:11 AM, John Larkin wrote:
> On Sat, 20 Jun 2015 09:08:31 -0400, bitrex > <bitrex@de.lete.earthlink.net> wrote: > >> I have a need to take a square pulse of 0V/+5V and about 5-10ms >> duration, and stretch it out long enough to flash a LED brightly enough >> to be visible indoors under "ordinary" lighting conditions. >> >> I currently only have op-amps on the board and would rather not add any >> logic ICs to do this. So using low-speed op amps and discretes would be >> fine. The pulse source into the stretcher would be low impedance. >> >> An optional feature would be to have the "stretch" duration decrease the >> more rapidly pulses are coming into the circuit. But that is not a >> requirement if it needs significant complexity. > > NPN emitter follower driving R-C to ground, then a comparator. Use an > opamp as the comparator. > >
I'm probably going to need to be using something like an LM324A. Will they work OK in that role?
In article <558565dc$0$23427$4c5ecfc7@frugalusenet.com>, 
bitrex@de.lete.earthlink.net says...
> > I have a need to take a square pulse of 0V/+5V and about 5-10ms > duration, and stretch it out long enough to flash a LED brightly enough > to be visible indoors under "ordinary" lighting conditions. > > I currently only have op-amps on the board and would rather not add any > logic ICs to do this. So using low-speed op amps and discretes would be > fine. The pulse source into the stretcher would be low impedance. > > An optional feature would be to have the "stretch" duration decrease the > more rapidly pulses are coming into the circuit. But that is not a > requirement if it needs significant complexity.
Inject the pulse via a diode to the (+) input of a op-amp. The (+) input will have a small cap on it going to common for the delay off with a R also going to common as part of the RC calculations. Put a voltage divider on the (-) input of the op-amp of lets say 2.0 volts, that will be your threshold for the comparator. You may also want to have a low current feed back from the output to the (+) input to aid in a little snap, hysteresis, for the off state. If for some reason your reference pulse appears to be very low current in nature, it could have issues driving the cap you select. If this is the case, buffer the pulse with another op-amp in unity mode or use a NPN trannie in emitter follower mode to drive it, in which case, you won't need the diode. Jamie
On 6/20/2015 11:42 AM, Jim Thompson wrote:
> On Sat, 20 Jun 2015 09:08:31 -0400, bitrex > <bitrex@de.lete.earthlink.net> wrote: > >> I have a need to take a square pulse of 0V/+5V and about 5-10ms >> duration, and stretch it out long enough to flash a LED brightly enough >> to be visible indoors under "ordinary" lighting conditions. >> >> I currently only have op-amps on the board and would rather not add any >> logic ICs to do this. So using low-speed op amps and discretes would be >> fine. The pulse source into the stretcher would be low impedance. >> >> An optional feature would be to have the "stretch" duration decrease the >> more rapidly pulses are coming into the circuit. But that is not a >> requirement if it needs significant complexity. > > Supplies? > > ...Jim Thompson >
Looks like it's going to be +5V virtual ground split into +2.5 and -2.5 at this point so they'll be low-voltage opamps.
In article <558597a3$0$6977$4c5ecfc7@frugalusenet.com>, 
bitrex@de.lete.earthlink.net says...
> > On 6/20/2015 11:11 AM, John Larkin wrote: > > On Sat, 20 Jun 2015 09:08:31 -0400, bitrex > > <bitrex@de.lete.earthlink.net> wrote: > > > >> I have a need to take a square pulse of 0V/+5V and about 5-10ms > >> duration, and stretch it out long enough to flash a LED brightly enough > >> to be visible indoors under "ordinary" lighting conditions. > >> > >> I currently only have op-amps on the board and would rather not add any > >> logic ICs to do this. So using low-speed op amps and discretes would be > >> fine. The pulse source into the stretcher would be low impedance. > >> > >> An optional feature would be to have the "stretch" duration decrease the > >> more rapidly pulses are coming into the circuit. But that is not a > >> requirement if it needs significant complexity. > > > > NPN emitter follower driving R-C to ground, then a comparator. Use an > > opamp as the comparator. > > > > > > I'm probably going to need to be using something like an LM324A. Will > they work OK in that role?
That will work just fine. Just keep in mind that a 324 gets closer to the bottom rail than it does the top rail. Infact, it can become detached but I don't think that should cause you any issues. Jamie
On 6/20/2015 12:49 PM, M Philbrook wrote:
> In article <558565dc$0$23427$4c5ecfc7@frugalusenet.com>, > bitrex@de.lete.earthlink.net says... >> >> I have a need to take a square pulse of 0V/+5V and about 5-10ms >> duration, and stretch it out long enough to flash a LED brightly enough >> to be visible indoors under "ordinary" lighting conditions. >> >> I currently only have op-amps on the board and would rather not add any >> logic ICs to do this. So using low-speed op amps and discretes would be >> fine. The pulse source into the stretcher would be low impedance. >> >> An optional feature would be to have the "stretch" duration decrease the >> more rapidly pulses are coming into the circuit. But that is not a >> requirement if it needs significant complexity. > > > Inject the pulse via a diode to the (+) input of a > op-amp. The (+) input will have a small cap on it going > to common for the delay off with a R also going to common > as part of the RC calculations. > > Put a voltage divider on the (-) input of the op-amp of > lets say 2.0 volts, that will be your threshold for the comparator. > > You may also want to have a low current feed back from the output > to the (+) input to aid in a little snap, hysteresis, for the off > state. > > If for some reason your reference pulse appears to be very low current > in nature, it could have issues driving the cap you select. If this is > the case, buffer the pulse with another op-amp in unity mode or use a > NPN trannie in emitter follower mode to drive it, in which case, you > won't need the diode. > > Jamie >
I'll explore that a bit in simulation, thanks.
On Sat, 20 Jun 2015 12:52:26 -0400, bitrex
<bitrex@de.lete.earthlink.net> wrote:

>On 6/20/2015 11:42 AM, Jim Thompson wrote: >> On Sat, 20 Jun 2015 09:08:31 -0400, bitrex >> <bitrex@de.lete.earthlink.net> wrote: >> >>> I have a need to take a square pulse of 0V/+5V and about 5-10ms >>> duration, and stretch it out long enough to flash a LED brightly enough >>> to be visible indoors under "ordinary" lighting conditions. >>> >>> I currently only have op-amps on the board and would rather not add any >>> logic ICs to do this. So using low-speed op amps and discretes would be >>> fine. The pulse source into the stretcher would be low impedance. >>> >>> An optional feature would be to have the "stretch" duration decrease the >>> more rapidly pulses are coming into the circuit. But that is not a >>> requirement if it needs significant complexity. >> >> Supplies? >> >> ...Jim Thompson >> > >Looks like it's going to be +5V virtual ground split into +2.5 and -2.5 >at this point so they'll be low-voltage opamps.
So your input pulse is -2.5V to +2.5V _relative_ to your virtual ground? ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: skypeanalog | | | 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.