Using an ADC0831 with higher voltages
I have a circuit that makes use of a 741 OP AMP to provide
an output to a stamp. EXAMPLE: The op amp is feed with a reference
voltage of exactly 16 volts. When the battery voltage is compared and
falls below X value, the stamp sees a state change from the output of
the 741 and does it's thing.
I want to use the ADC0831 to monitor this voltage, which could be as
high as 14 volts if the string is under charge. Reading the specs for
this device, it appears that max input for Vin is VCC+ .3 volts
period.
I assume I need to create a voltage divider, but what I'd really like
to do is use the 0831 to look at 10 > 15 volts, and not the rest of
the scale, that is to say "0" decimal out would be <= 10 volts.
I'm sure I don't know the easiest way to approach this, and any hints
would be real welcome.
Thanks in advance,
gbrecke
an output to a stamp. EXAMPLE: The op amp is feed with a reference
voltage of exactly 16 volts. When the battery voltage is compared and
falls below X value, the stamp sees a state change from the output of
the 741 and does it's thing.
I want to use the ADC0831 to monitor this voltage, which could be as
high as 14 volts if the string is under charge. Reading the specs for
this device, it appears that max input for Vin is VCC+ .3 volts
period.
I assume I need to create a voltage divider, but what I'd really like
to do is use the 0831 to look at 10 > 15 volts, and not the rest of
the scale, that is to say "0" decimal out would be <= 10 volts.
I'm sure I don't know the easiest way to approach this, and any hints
would be real welcome.
Thanks in advance,
gbrecke
Comments
amp. Burr-Brown INA105 application notes describes a circuit (Figure
10) which does this.
Dennis
Original Message
From: George B. [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=HpGK7ynXKPayD-BGMlmqYnNCgoTvquVWh2AgbquOvp4delvGiXx8QCTZaYDcJRmhPhJ47Ck_-X6iEgU]gbrecke@y...[/url
Sent: Saturday, December 01, 2001 10:32 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Using an ADC0831 with higher voltages
I have a circuit that makes use of a 741 OP AMP to provide
an output to a stamp. EXAMPLE: The op amp is feed with a reference
voltage of exactly 16 volts. When the battery voltage is compared and
falls below X value, the stamp sees a state change from the output of
the 741 and does it's thing.
I want to use the ADC0831 to monitor this voltage, which could be as
high as 14 volts if the string is under charge. Reading the specs for
this device, it appears that max input for Vin is VCC+ .3 volts
period.
I assume I need to create a voltage divider, but what I'd really like
to do is use the 0831 to look at 10 > 15 volts, and not the rest of
the scale, that is to say "0" decimal out would be <= 10 volts.
I'm sure I don't know the easiest way to approach this, and any hints
would be real welcome.
Thanks in advance,
gbrecke
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Thank you both for help in this matter, I just received an additional
3 ADCs in the mail today, hopefully I won't smoke another one!
Best Wishes,
George B.
--- In basicstamps@y..., "peter verkaik" <peterverkaik@b...> wrote:
> Hi,
>
> One way is to feed a reference voltage to the negative input of an
opamp
> like this:
> Create a 2.5V reference voltage using a 1k resistor and reference
diode
> between
> VCC (+5V) and GND.
> Connect a resistor R1 between opamp output and opamp - input
> Connect a resistor R2 between opamp - input and diode 2.5V
> Make a resistor divider R2/(R1+R2) for the monitored voltage Vin
and connect
> the divider crosspoint to the opamp + input.
>
> The opamp now has the following output:
>
> Vout = (R2/(R1+R2))*Vin*((R1+R2)/R2) - (R1/R2)*2.5V
> = Vin - (R1/R2)*2.5V
>
> Let R1/R2 be 4, then Vout = Vin - 10V
> If Vin<=10V the opamp output will be pulled to ground
> For Vin>=15V the opamp output will be near VCC (+5V).
>
> The opamp can be opearated from a single 5V supply.
> The resistors R1 and R2 (two of each) should match as close
> as possible to get the above output function with minimal error.
> Hope this helps.
>
> Regards peter
>
>
>
Oorspronkelijk bericht
> Van: Dennis P. O'Leary [noparse][[/noparse]mailto:doleary@h...]
> Verzonden: maandag 3 december 2001 10:02
> Aan: basicstamps@y...
> Onderwerp: RE: [noparse][[/noparse]basicstamps] Using an ADC0831 with higher voltages
>
> A single-chip solution is to build a pseudoground generator using
an op
> amp. Burr-Brown INA105 application notes describes a circuit
(Figure
> 10) which does this.
>
> Dennis
>
>
Original Message
> From: George B. [noparse][[/noparse]mailto:gbrecke@y...]
> Sent: Saturday, December 01, 2001 10:32 PM
> To: basicstamps@y...
> Subject: [noparse][[/noparse]basicstamps] Using an ADC0831 with higher voltages
>
>
> I have a circuit that makes use of a 741 OP AMP to provide
> an output to a stamp. EXAMPLE: The op amp is feed with a reference
> voltage of exactly 16 volts. When the battery voltage is compared
and
> falls below X value, the stamp sees a state change from the output
of
> the 741 and does it's thing.
>
> I want to use the ADC0831 to monitor this voltage, which could be as
> high as 14 volts if the string is under charge. Reading the specs
for
> this device, it appears that max input for Vin is VCC+ .3 volts
> period.
>
> I assume I need to create a voltage divider, but what I'd really
like
> to do is use the 0831 to look at 10 > 15 volts, and not the rest of
> the scale, that is to say "0" decimal out would be <= 10 volts.
>
> I'm sure I don't know the easiest way to approach this, and any
hints
> would be real welcome.
>
> Thanks in advance,
>
> gbrecke
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@y...
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Subject
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One way is to feed a reference voltage to the negative input of an opamp
like this:
Create a 2.5V reference voltage using a 1k resistor and reference diode
between
VCC (+5V) and GND.
Connect a resistor R1 between opamp output and opamp - input
Connect a resistor R2 between opamp - input and diode 2.5V
Make a resistor divider R2/(R1+R2) for the monitored voltage Vin and connect
the divider crosspoint to the opamp + input.
The opamp now has the following output:
Vout = (R2/(R1+R2))*Vin*((R1+R2)/R2) - (R1/R2)*2.5V
= Vin - (R1/R2)*2.5V
Let R1/R2 be 4, then Vout = Vin - 10V
If Vin<=10V the opamp output will be pulled to ground
For Vin>=15V the opamp output will be near VCC (+5V).
The opamp can be opearated from a single 5V supply.
The resistors R1 and R2 (two of each) should match as close
as possible to get the above output function with minimal error.
Hope this helps.
Regards peter
Oorspronkelijk bericht
Van: Dennis P. O'Leary [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=x_s5fQsR_5boyOQ-JnREKAncqNXAGv6H23_yAw4C1XrvXeCz4wSJ5y2NidWbIGP7IWR_c0yke6WS]doleary@h...[/url
Verzonden: maandag 3 december 2001 10:02
Aan: basicstamps@yahoogroups.com
Onderwerp: RE: [noparse][[/noparse]basicstamps] Using an ADC0831 with higher voltages
A single-chip solution is to build a pseudoground generator using an op
amp. Burr-Brown INA105 application notes describes a circuit (Figure
10) which does this.
Dennis
Original Message
From: George B. [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=A8-fV2wzwa7LBbzCc-QtHuY4AHq_8ohuMvbYgWeoA-j8DBmZQV3UhGUVkvX6fXUwg6QJTA3fXFE]gbrecke@y...[/url
Sent: Saturday, December 01, 2001 10:32 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Using an ADC0831 with higher voltages
I have a circuit that makes use of a 741 OP AMP to provide
an output to a stamp. EXAMPLE: The op amp is feed with a reference
voltage of exactly 16 volts. When the battery voltage is compared and
falls below X value, the stamp sees a state change from the output of
the 741 and does it's thing.
I want to use the ADC0831 to monitor this voltage, which could be as
high as 14 volts if the string is under charge. Reading the specs for
this device, it appears that max input for Vin is VCC+ .3 volts
period.
I assume I need to create a voltage divider, but what I'd really like
to do is use the 0831 to look at 10 > 15 volts, and not the rest of
the scale, that is to say "0" decimal out would be <= 10 volts.
I'm sure I don't know the easiest way to approach this, and any hints
would be real welcome.
Thanks in advance,
gbrecke
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