BS2 Project and ADC''s
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Posts: 46,084
>Okay, let me try a different approach. Sometimes I don't give enough info
>and sometimes too much info.
>I would like to read a sensor with a BS2, I know I will need an ADC, which
>needs to be a 12 bit. Can anyone recommend an serial ADC with possibly a
>4.096 built reference? I've used the 1298 before but I wanted something a
>little more precise and since the 1298 uses the Vcc as it's reference I
>wanted to avoid it (Unless someone has a great method to make it very
>accurate and repeatable).
Do you need just one channel? You may need more sooner or later. I
like the TLC2543, which has 11 input channels.
<http://www.emesystems.com/OWL2face.htm#TLC2543> It needs an external
reference. Another series with good Stamp documentation is the
single channel MAX187 (with 4.096 internal reference) or MAX189
(external reference) or 8 channel MAX186 (4.096 internal) or MAX188
(external). One disadvantage of an internal reference is that they
are usually not very accurate (i.e. +/- 2%) , and you can't adjust
them with an external potentiometer. You end up having to do
corrections in software.
>
>The next part does not pertain to a stamp, but does have something to do
>with my project, if you can't help, at least try and point me in the right
>direction.
>
>The max my sensor puts out is 400mv, so I figured I would use an
>instrumentation amp to increase this signal by approx. 10 x with a small
>adjustment for calibration purposes. This would give me the full range of my
>ADC and the best resolution, I think. The amp needs to be a single
>voltage like + 5vdc and Grd. I was looking at the AD626 and I several
>LTC1052's but I never used them before. Can someone tell me if I'm on the
>right path or if they have another item which is easy to work with and is
>fairly accurate?
I use the LTC1051 (dual CAZ op amp) a lot when DC accuracy is
paramount--input offsets of less than 10 microvolts. I think the
LTC1052 is similar. Don't expect it to swing above 3.5 volts when it
has a 5 volt supply. Maybe you can power it from the higher
unregulated voltage. Or limit your amplification to x5 instead of
x10, and use a 2.5 volt reference on your ADC. Or just accept 11
bits resolution. I don't know of any rail to rail op-amps that are
terrifically accurate, but they would certainly work if you want to
adjust both the input offset and the scale factor with pots. Is the
Oxygen sensor really that accurate and stable? The op amp circuit
will be really simple, especially if you use the CAZ op amp. The
classic non-inverting amplifier.
>
>I don't mind learning by hard knocks, but I rather not do it a dozen times
>either.
>Throw me a bone please....
>Richard
Don't worry, you still get the hard knocks. The bone falling may hit
you on the head. A corollary of Murphy's law.
-- Tracy
>
>
>
Original Message
>From: "Richard Skinner" <rwskinner@w...>
>To: <basicstamps@yahoogroups.com>
>Sent: Monday, October 13, 2003 1:04 PM
>Subject: [noparse][[/noparse]basicstamps] Sensor project
>
>
>> I working on a small project which requires me to read a sensor which
>> outputs from 0 mv to 400mv +/- 40 mv full scale. It's almost linear but
>> does have a couple of items that could use some error correction. I have
>> several questions regarding the electronics end and some on the math end.
>> The sensor is an Oxygen sensor that reads from 0% to 25.5% o2. At 21% o2
>it
>> reads approx. 400mv.
>>
>> I don't know much about OP Amps but willing to learn. I figured I would
>use
>> an 8 bit ADC with a 4.096 reference, then use an OP Amp with a Gain of 10.
>> I thought about using a pot to slightly adjust the gain in order to
>> calibrate the sensor. The sensor always has zero output when it senses
>zero
>> input, so I was only going to adjust the high end. Would this be the
>proper
>> procedure?
>>
>> Next, the sensor exhibits a Temp Coefficient of 0.2% signal / Degree C so
>I
>> may want to perform a temp. correction for the temp at the sensor. The
>temp
>> would range from about Ambient (32F to 100F) to about 150 Degree F when
>> operating in it's environment. It's calibrated in an Ambient condition.
>I
>> was leaning towards using an Thermistor to measure the temp during
>> calibration, then correcting the displayed units for the operating temps.
>>
>> Any input would be greatly appreciated.
>> Richard
>>
>>
>>
>>
>> To UNSUBSCRIBE, just send mail to:
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>>
>>
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>>
>>
>
>
>To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
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>Subject and Body of the message will be ignored.
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>and sometimes too much info.
>I would like to read a sensor with a BS2, I know I will need an ADC, which
>needs to be a 12 bit. Can anyone recommend an serial ADC with possibly a
>4.096 built reference? I've used the 1298 before but I wanted something a
>little more precise and since the 1298 uses the Vcc as it's reference I
>wanted to avoid it (Unless someone has a great method to make it very
>accurate and repeatable).
Do you need just one channel? You may need more sooner or later. I
like the TLC2543, which has 11 input channels.
<http://www.emesystems.com/OWL2face.htm#TLC2543> It needs an external
reference. Another series with good Stamp documentation is the
single channel MAX187 (with 4.096 internal reference) or MAX189
(external reference) or 8 channel MAX186 (4.096 internal) or MAX188
(external). One disadvantage of an internal reference is that they
are usually not very accurate (i.e. +/- 2%) , and you can't adjust
them with an external potentiometer. You end up having to do
corrections in software.
>
>The next part does not pertain to a stamp, but does have something to do
>with my project, if you can't help, at least try and point me in the right
>direction.
>
>The max my sensor puts out is 400mv, so I figured I would use an
>instrumentation amp to increase this signal by approx. 10 x with a small
>adjustment for calibration purposes. This would give me the full range of my
>ADC and the best resolution, I think. The amp needs to be a single
>voltage like + 5vdc and Grd. I was looking at the AD626 and I several
>LTC1052's but I never used them before. Can someone tell me if I'm on the
>right path or if they have another item which is easy to work with and is
>fairly accurate?
I use the LTC1051 (dual CAZ op amp) a lot when DC accuracy is
paramount--input offsets of less than 10 microvolts. I think the
LTC1052 is similar. Don't expect it to swing above 3.5 volts when it
has a 5 volt supply. Maybe you can power it from the higher
unregulated voltage. Or limit your amplification to x5 instead of
x10, and use a 2.5 volt reference on your ADC. Or just accept 11
bits resolution. I don't know of any rail to rail op-amps that are
terrifically accurate, but they would certainly work if you want to
adjust both the input offset and the scale factor with pots. Is the
Oxygen sensor really that accurate and stable? The op amp circuit
will be really simple, especially if you use the CAZ op amp. The
classic non-inverting amplifier.
>
>I don't mind learning by hard knocks, but I rather not do it a dozen times
>either.
>Throw me a bone please....
>Richard
Don't worry, you still get the hard knocks. The bone falling may hit
you on the head. A corollary of Murphy's law.
-- Tracy
>
>
>
Original Message
>From: "Richard Skinner" <rwskinner@w...>
>To: <basicstamps@yahoogroups.com>
>Sent: Monday, October 13, 2003 1:04 PM
>Subject: [noparse][[/noparse]basicstamps] Sensor project
>
>
>> I working on a small project which requires me to read a sensor which
>> outputs from 0 mv to 400mv +/- 40 mv full scale. It's almost linear but
>> does have a couple of items that could use some error correction. I have
>> several questions regarding the electronics end and some on the math end.
>> The sensor is an Oxygen sensor that reads from 0% to 25.5% o2. At 21% o2
>it
>> reads approx. 400mv.
>>
>> I don't know much about OP Amps but willing to learn. I figured I would
>use
>> an 8 bit ADC with a 4.096 reference, then use an OP Amp with a Gain of 10.
>> I thought about using a pot to slightly adjust the gain in order to
>> calibrate the sensor. The sensor always has zero output when it senses
>zero
>> input, so I was only going to adjust the high end. Would this be the
>proper
>> procedure?
>>
>> Next, the sensor exhibits a Temp Coefficient of 0.2% signal / Degree C so
>I
>> may want to perform a temp. correction for the temp at the sensor. The
>temp
>> would range from about Ambient (32F to 100F) to about 150 Degree F when
>> operating in it's environment. It's calibrated in an Ambient condition.
>I
>> was leaning towards using an Thermistor to measure the temp during
>> calibration, then correcting the displayed units for the operating temps.
>>
>> Any input would be greatly appreciated.
>> 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:
> 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/