How to make logic signal from amplifier output? (Need output offset voltage.)
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Posts: 46,084
Richard,
I think the way to go about it is look at the underlying circuit of a
Schmitt trigger - what makes it work?
The key is that is is a comparator with hysteresis. If you design your own
using an op-amp you can make it do whatever you want. The circuit should be
available in op-amp cookbooks, but I have seen it in The Art of Electronics
by Horowitz and Hill.
Regards,
Kyle
R. Kyle Schmidt, P. Eng.
Control System Specialist
Messier-Dowty Inc. "The Landing Gear Company"
kyle.schmidt@m...
>
Original Message
> From: Richard Warner [noparse]/noparse]SMTP:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=mvcLgVYSThVEq-WYVU2E89I_p8FLpB8cuJlLqXRfZIsati1AfHAjxThsP5ks2-gnzJkZXDc]rwarner@p...[/url
> Sent: Monday, October 16, 2000 1:13 PM
> To: basicstamps@egroups.com
> Subject: [noparse][[/noparse]basicstamps] How to make logic signal from amplifier
> output? (Need output offset voltage.)
>
> Hi all -
>
> I´m working on a BSII project that requires converting output from a
> sensor into a digital logic signal. It is easy to run the output into a
> schmitt trigger but this has several problems. The trigger turns on at
> 2.2v
> and off at 1.5v. My sensor output (through an amplifier) thus has to go
> all
> the way from zero to 2.2 to turn it on, and then all the way down to 1.5
> to
> change state. I lose a huge amount of sensitivity this way.
> The way I desire, and am trying to figure out how to do...is as
> follows.
> I want to be able to adjust an offset voltage to let´s say 1.3 volts. In
> such a way that the output from the amp adds to it and so only 0.9v from
> the
> sensor´s amp is required to output an ON. The adjustment would allow me
> to
> reduce sensitivity by lowering the offset voltage all the way down to zero
>
> volts as the minimum sensitivity. I can adjust the amp gain to set the
> sweet spot where I want.
> Even better would be a trick that would reduce the 0.7v range for
> changing state. Would be great if I could change state with only a 0.3v
> swing.
> Clues/hints for a low-power (let´s say 5ma) circuit would be greatly
> appreciated. Seems like would be a useful, general purpose circuit for
> many
> applications too.
>
> Thanks for the info
>
> Rich
> _________________________________________________________________________
> Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.
>
> Share information about yourself, create your own public profile at
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>
>
I think the way to go about it is look at the underlying circuit of a
Schmitt trigger - what makes it work?
The key is that is is a comparator with hysteresis. If you design your own
using an op-amp you can make it do whatever you want. The circuit should be
available in op-amp cookbooks, but I have seen it in The Art of Electronics
by Horowitz and Hill.
Regards,
Kyle
R. Kyle Schmidt, P. Eng.
Control System Specialist
Messier-Dowty Inc. "The Landing Gear Company"
kyle.schmidt@m...
>
Original Message
> From: Richard Warner [noparse]/noparse]SMTP:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=mvcLgVYSThVEq-WYVU2E89I_p8FLpB8cuJlLqXRfZIsati1AfHAjxThsP5ks2-gnzJkZXDc]rwarner@p...[/url
> Sent: Monday, October 16, 2000 1:13 PM
> To: basicstamps@egroups.com
> Subject: [noparse][[/noparse]basicstamps] How to make logic signal from amplifier
> output? (Need output offset voltage.)
>
> Hi all -
>
> I´m working on a BSII project that requires converting output from a
> sensor into a digital logic signal. It is easy to run the output into a
> schmitt trigger but this has several problems. The trigger turns on at
> 2.2v
> and off at 1.5v. My sensor output (through an amplifier) thus has to go
> all
> the way from zero to 2.2 to turn it on, and then all the way down to 1.5
> to
> change state. I lose a huge amount of sensitivity this way.
> The way I desire, and am trying to figure out how to do...is as
> follows.
> I want to be able to adjust an offset voltage to let´s say 1.3 volts. In
> such a way that the output from the amp adds to it and so only 0.9v from
> the
> sensor´s amp is required to output an ON. The adjustment would allow me
> to
> reduce sensitivity by lowering the offset voltage all the way down to zero
>
> volts as the minimum sensitivity. I can adjust the amp gain to set the
> sweet spot where I want.
> Even better would be a trick that would reduce the 0.7v range for
> changing state. Would be great if I could change state with only a 0.3v
> swing.
> Clues/hints for a low-power (let´s say 5ma) circuit would be greatly
> appreciated. Seems like would be a useful, general purpose circuit for
> many
> applications too.
>
> Thanks for the info
>
> Rich
> _________________________________________________________________________
> Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.
>
> Share information about yourself, create your own public profile at
> http://profiles.msn.com.
>
>
>
Comments
steps to work with, some have voltage reff pins for setting the upper
voltage so now you have 256 steps from 0 to 2.56 volts would this
give you the res your looking for
"Schmidt, Kyle" wrote:
>
> Richard,
>
> I think the way to go about it is look at the underlying circuit of a
> Schmitt trigger - what makes it work?
>
> The key is that is is a comparator with hysteresis. If you design your own
> using an op-amp you can make it do whatever you want. The circuit should be
> available in op-amp cookbooks, but I have seen it in The Art of Electronics
> by Horowitz and Hill.
>
> Regards,
>
> Kyle
>
> R. Kyle Schmidt, P. Eng.
> Control System Specialist
> Messier-Dowty Inc. "The Landing Gear Company"
> kyle.schmidt@m...
>
> >
Original Message
> > From: Richard Warner [noparse]/noparse]SMTP:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=wOVtgaiTZq3Rt503yn1wrnf8dzS5-UuPnW11GhvJQvQFJHEyv_LDN3xjWUXDvACjHkpnxxIJy38]rwarner@p...[/url
> > Sent: Monday, October 16, 2000 1:13 PM
> > To: basicstamps@egroups.com
> > Subject: [noparse][[/noparse]basicstamps] How to make logic signal from amplifier
> > output? (Need output offset voltage.)
> >
> > Hi all -
> >
> > I´m working on a BSII project that requires converting output from a
> > sensor into a digital logic signal. It is easy to run the output into a
> > schmitt trigger but this has several problems. The trigger turns on at
> > 2.2v
> > and off at 1.5v. My sensor output (through an amplifier) thus has to go
> > all
> > the way from zero to 2.2 to turn it on, and then all the way down to 1.5
> > to
> > change state. I lose a huge amount of sensitivity this way.
> > The way I desire, and am trying to figure out how to do...is as
> > follows.
> > I want to be able to adjust an offset voltage to let´s say 1.3 volts. In
> > such a way that the output from the amp adds to it and so only 0.9v from
> > the
> > sensor´s amp is required to output an ON. The adjustment would allow me
> > to
> > reduce sensitivity by lowering the offset voltage all the way down to zero
> >
> > volts as the minimum sensitivity. I can adjust the amp gain to set the
> > sweet spot where I want.
> > Even better would be a trick that would reduce the 0.7v range for
> > changing state. Would be great if I could change state with only a 0.3v
> > swing.
> > Clues/hints for a low-power (let´s say 5ma) circuit would be greatly
> > appreciated. Seems like would be a useful, general purpose circuit for
> > many
> > applications too.
> >
> > Thanks for the info
> >
> > Rich
> > _________________________________________________________________________
> > Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.
> >
> > Share information about yourself, create your own public profile at
> > http://profiles.msn.com.
> >
> >
> >
I´m working on a BSII project that requires converting output from a
sensor into a digital logic signal. It is easy to run the output into a
schmitt trigger but this has several problems. The trigger turns on at 2.2v
and off at 1.5v. My sensor output (through an amplifier) thus has to go all
the way from zero to 2.2 to turn it on, and then all the way down to 1.5 to
change state. I lose a huge amount of sensitivity this way.
The way I desire, and am trying to figure out how to do...is as follows.
I want to be able to adjust an offset voltage to let´s say 1.3 volts. In
such a way that the output from the amp adds to it and so only 0.9v from the
sensor´s amp is required to output an ON. The adjustment would allow me to
reduce sensitivity by lowering the offset voltage all the way down to zero
volts as the minimum sensitivity. I can adjust the amp gain to set the
sweet spot where I want.
Even better would be a trick that would reduce the 0.7v range for
changing state. Would be great if I could change state with only a 0.3v
swing.
Clues/hints for a low-power (let´s say 5ma) circuit would be greatly
appreciated. Seems like would be a useful, general purpose circuit for many
applications too.
Thanks for the info
Rich
_________________________________________________________________________
Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.
Share information about yourself, create your own public profile at
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scalable digital output from? If so, it's easiest to input your sensor to an
ADC then scale it to do whatever you want at the stamp output with your
program. I don't think you can do that with 5 mA, though....
Original Message
From: Richard Warner [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=FowpgxlGWZcU8P18b5eyo6_r3cODTLiL2oBymhy4Cs7RKFMGzhn7LMCbiD_VENAvPv7CVp8kiMl6]rwarner@p...[/url
Sent: Monday, October 16, 2000 12:13 PM
To: basicstamps@egroups.com
Subject: [noparse][[/noparse]basicstamps] How to make logic signal from amplifier output?
(Need output offset voltage.)
Hi all -
I´m working on a BSII project that requires converting output from a
sensor into a digital logic signal. It is easy to run the output into a
schmitt trigger but this has several problems. The trigger turns on at 2.2v
and off at 1.5v. My sensor output (through an amplifier) thus has to go all
the way from zero to 2.2 to turn it on, and then all the way down to 1.5 to
change state. I lose a huge amount of sensitivity this way.
The way I desire, and am trying to figure out how to do...is as follows.
I want to be able to adjust an offset voltage to let´s say 1.3 volts. In
such a way that the output from the amp adds to it and so only 0.9v from the
sensor´s amp is required to output an ON. The adjustment would allow me to
reduce sensitivity by lowering the offset voltage all the way down to zero
volts as the minimum sensitivity. I can adjust the amp gain to set the
sweet spot where I want.
Even better would be a trick that would reduce the 0.7v range for
changing state. Would be great if I could change state with only a 0.3v
swing.
Clues/hints for a low-power (let´s say 5ma) circuit would be greatly
appreciated. Seems like would be a useful, general purpose circuit for many
applications too.
Thanks for the info
Rich
_________________________________________________________________________
Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.
Share information about yourself, create your own public profile at
http://profiles.msn.com.