need help on op-amp design for ceramic gyro
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Posts: 46,084
I am using a tokin cg-16d on a project. I used a 741 op-amp in differential
mode with a gain of 20. A gain of 20 gives me a 5 volt swing over the speeds
that I am interested in. One input to the op-amp is the 2.5 volt reference
voltage from the gyro and the other input is the output of the gyro. The
gyro has 2.5 volts as its output for zero motion and swings 0.125 volts in
each direction. By using a differential mode I can amplify the signal to
the desired value. I thought that I could use the offset voltage terminals
on the op-amp to place the zero output of the amplified signal back at 2.5
volts. But it doesnt seem to work that way. My goal is to end up with signal
that varies from 0 to 5 volts and have its no motion output indicate 2.5
volts.
what have I done wrong ?
is there a better way to do this ?
thanks
Richard
mode with a gain of 20. A gain of 20 gives me a 5 volt swing over the speeds
that I am interested in. One input to the op-amp is the 2.5 volt reference
voltage from the gyro and the other input is the output of the gyro. The
gyro has 2.5 volts as its output for zero motion and swings 0.125 volts in
each direction. By using a differential mode I can amplify the signal to
the desired value. I thought that I could use the offset voltage terminals
on the op-amp to place the zero output of the amplified signal back at 2.5
volts. But it doesnt seem to work that way. My goal is to end up with signal
that varies from 0 to 5 volts and have its no motion output indicate 2.5
volts.
what have I done wrong ?
is there a better way to do this ?
thanks
Richard
Comments
Two suggestions. 1) Use a Burr-Brown INA105 instead of the 741 as a
"precision subtractor" (see application notes from Burr-Brown). It provides
internal laser trimmed 25K input and feedback resistors. 2) Use a second op
amp to add the 2.5 volts back in along with your sensor signal, after
amplification. A trim pot (about 5K) should be used to provide the
necessary voltage in a voltage divider circuit from one of the bias
voltages. Note that the trim voltage range should be about 2.5V/20, for
your required final gain of 20.
I'm using essentially the same circuit approach with a Murata sensor, which
is similar to the Tokin.
Dennis
Original Message
From: Richard Friedrich [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=sLQ_N1sOQMcblGogb74G_POXLAsbzW43yrttHO7Z-5wS872VetL8M0S4DIgkCtX7Pq4X93XvG2OZ00Bsd31_]rfriedrich@a...[/url
Sent: Wednesday, August 22, 2001 12:35 PM
To: basicstamps@yahoogroups.com; basicx@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] need help on op-amp design for ceramic gyro
I am using a tokin cg-16d on a project. I used a 741 op-amp in differential
mode with a gain of 20. A gain of 20 gives me a 5 volt swing over the speeds
that I am interested in. One input to the op-amp is the 2.5 volt reference
voltage from the gyro and the other input is the output of the gyro. The
gyro has 2.5 volts as its output for zero motion and swings 0.125 volts in
each direction. By using a differential mode I can amplify the signal to
the desired value. I thought that I could use the offset voltage terminals
on the op-amp to place the zero output of the amplified signal back at 2.5
volts. But it doesnt seem to work that way. My goal is to end up with signal
that varies from 0 to 5 volts and have its no motion output indicate 2.5
volts.
what have I done wrong ?
is there a better way to do this ?
thanks
Richard
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weight and space is at a premium. I solved my problem shortly after I made
my post. I just put a pot across the power supply and put the wiper to the
non-inverting terminal. The offset voltage is added to the reference voltage
and then the difference between that sum and the signal is amplified such
that you just dial in the amount of offset (with in reason).
I also converted it to a single power supply but that halfed my output in a
way that more gain doesnt help. I have a two volt swing rahter than a 5 volt
swing - still plenty of resolution with 12 bit a/d. I may use 10 or 15 volt
supply to op-amp (probably not).
I have used burr/brown instrumentation amps before - nice stuff!
thanks
richard
Original Message
From: "Dennis P. O'Leary" <doleary@h...>
To: <basicstamps@yahoogroups.com>
Sent: Wednesday, August 22, 2001 7:41 PM
Subject: RE: [noparse][[/noparse]basicstamps] need help on op-amp design for ceramic gyro
> Richard,
>
> Two suggestions. 1) Use a Burr-Brown INA105 instead of the 741 as a
> "precision subtractor" (see application notes from Burr-Brown). It
provides
> internal laser trimmed 25K input and feedback resistors. 2) Use a second
op
> amp to add the 2.5 volts back in along with your sensor signal, after
> amplification. A trim pot (about 5K) should be used to provide the
> necessary voltage in a voltage divider circuit from one of the bias
> voltages. Note that the trim voltage range should be about 2.5V/20, for
> your required final gain of 20.
>
> I'm using essentially the same circuit approach with a Murata sensor,
which
> is similar to the Tokin.
>
> Dennis
>
>
Original Message
> From: Richard Friedrich [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=O6riRf4UASliR3fvkP2tBN3xz4MuobkCO-qNEYWLLpAimKSVcxpZpZrwA1kG0xHQH9Z1EjEyoRW5XCIbCWnUUsmO]rfriedrich@a...[/url
> Sent: Wednesday, August 22, 2001 12:35 PM
> To: basicstamps@yahoogroups.com; basicx@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] need help on op-amp design for ceramic gyro
>
>
> I am using a tokin cg-16d on a project. I used a 741 op-amp in
differential
> mode with a gain of 20. A gain of 20 gives me a 5 volt swing over the
speeds
> that I am interested in. One input to the op-amp is the 2.5 volt
reference
> voltage from the gyro and the other input is the output of the gyro. The
> gyro has 2.5 volts as its output for zero motion and swings 0.125 volts in
> each direction. By using a differential mode I can amplify the signal to
> the desired value. I thought that I could use the offset voltage terminals
> on the op-amp to place the zero output of the amplified signal back at
2.5
> volts. But it doesnt seem to work that way. My goal is to end up with
signal
> that varies from 0 to 5 volts and have its no motion output indicate 2.5
> volts.
>
> what have I done wrong ?
>
> is there a better way to do this ?
>
>
> thanks
>
>
> Richard
>
>
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
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> Body of the message will be ignored.
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>
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>
>
MAX187 12-bit A/D converter. That provides a clean linear range of 4.096 V,
and also prevents overdriving the MAX187 at more than 5 volts, which can
blow it up.
Dennis
Original Message
From: Richard Friedrich [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=HZn--EIF_bSbXo-2Vk57VxMWJabJWZfhEhGnHyDWuHZdjwCDEz0JlZj6eva2rWFRgS5BP41FU8C083-ymPTAiB0]rfriedrich@a...[/url
Sent: Wednesday, August 22, 2001 8:27 PM
To: basicstamps@yahoogroups.com
Subject: Re: [noparse][[/noparse]basicstamps] need help on p-amp design for ceramic gyro
thanks for the help, I may do that. But since this is on a little helicopter
weight and space is at a premium. I solved my problem shortly after I made
my post. I just put a pot across the power supply and put the wiper to the
non-inverting terminal. The offset voltage is added to the reference voltage
and then the difference between that sum and the signal is amplified such
that you just dial in the amount of offset (with in reason).
I also converted it to a single power supply but that halfed my output in a
way that more gain doesnt help. I have a two volt swing rahter than a 5 volt
swing - still plenty of resolution with 12 bit a/d. I may use 10 or 15 volt
supply to op-amp (probably not).
I have used burr/brown instrumentation amps before - nice stuff!
thanks
richard
Original Message
From: "Dennis P. O'Leary" <doleary@h...>
To: <basicstamps@yahoogroups.com>
Sent: Wednesday, August 22, 2001 7:41 PM
Subject: RE: [noparse][[/noparse]basicstamps] need help on op-amp design for ceramic gyro
> Richard,
>
> Two suggestions. 1) Use a Burr-Brown INA105 instead of the 741 as a
> "precision subtractor" (see application notes from Burr-Brown). It
provides
> internal laser trimmed 25K input and feedback resistors. 2) Use a second
op
> amp to add the 2.5 volts back in along with your sensor signal, after
> amplification. A trim pot (about 5K) should be used to provide the
> necessary voltage in a voltage divider circuit from one of the bias
> voltages. Note that the trim voltage range should be about 2.5V/20, for
> your required final gain of 20.
>
> I'm using essentially the same circuit approach with a Murata sensor,
which
> is similar to the Tokin.
>
> Dennis
>
>
Original Message
> From: Richard Friedrich [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=HZn--EIF_bSbXo-2Vk57VxMWJabJWZfhEhGnHyDWuHZdjwCDEz0JlZj6eva2rWFRgS5BP41FU8C083-ymPTAiB0]rfriedrich@a...[/url
> Sent: Wednesday, August 22, 2001 12:35 PM
> To: basicstamps@yahoogroups.com; basicx@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] need help on op-amp design for ceramic gyro
>
>
> I am using a tokin cg-16d on a project. I used a 741 op-amp in
differential
> mode with a gain of 20. A gain of 20 gives me a 5 volt swing over the
speeds
> that I am interested in. One input to the op-amp is the 2.5 volt
reference
> voltage from the gyro and the other input is the output of the gyro. The
> gyro has 2.5 volts as its output for zero motion and swings 0.125 volts in
> each direction. By using a differential mode I can amplify the signal to
> the desired value. I thought that I could use the offset voltage terminals
> on the op-amp to place the zero output of the amplified signal back at
2.5
> volts. But it doesnt seem to work that way. My goal is to end up with
signal
> that varies from 0 to 5 volts and have its no motion output indicate 2.5
> volts.
>
> what have I done wrong ?
>
> is there a better way to do this ?
>
>
> thanks
>
>
> Richard
>
>
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
> Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
> To UNSUBSCRIBE, just send mail to:
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>
>
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