ADC08831 Help needed

Archiver

If anyone can help with sample programs using the ADC08831 Analog-to-
Digital IC, I would greatly appreciate it. I'm trying to get a
reading from an LM35DT teperature sensor (10mV/degree C) and I'm
having a little difficulty. When I do shiftin AD,CLK,MSBPOST,
[noparse][[/noparse]theData] I seem to lose the last bit while adding an extra 0 bit at
the beginning so I am doing shiftin AD,CLK,MSBPOST,[noparse][[/noparse]theData\9]. I'm
not exactly sure what I am doing wrong (if anything) so any help
would be GREATLY appreciated!

-special [noparse][[/noparse]k]

Archiver

Can you post a sample of the code?

---

Original Message

---

From: special_4k4 [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=2r0ZQ--MCTLWv6X-T6pwf41S85HgpCwPtAQ9ioHubSTaAnVoY5_Bsi012ipqFvm4wyaQhZm-6ye_npQ]special_4k4@y...[/url
Sent: Monday, January 07, 2002 10:48 PM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] ADC08831 Help needed

If anyone can help with sample programs using the ADC08831 Analog-to-
Digital IC, I would greatly appreciate it. I'm trying to get a
reading from an LM35DT teperature sensor (10mV/degree C) and I'm
having a little difficulty. When I do shiftin AD,CLK,MSBPOST,
[noparse][[/noparse]theData] I seem to lose the last bit while adding an extra 0 bit at
the beginning so I am doing shiftin AD,CLK,MSBPOST,[noparse][[/noparse]theData\9]. I'm
not exactly sure what I am doing wrong (if anything) so any help
would be GREATLY appreciated!

-special [noparse][[/noparse]k]


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Archiver

This is what I am doing now to measure the temperature (in C):

---

'LM35DT:
'Pin 1->5V
'Pin 2->GND
'Pin 3->Pin 2 on ADC08831
'
'ADC08831:
' Pin 0 1--U--8 5V
'Pin 3 of LM35DT 2 7 Pin 2
' GND 3 6 Pin 1
' GND 4

---

5 Ref. Voltage (2.55V using
potentiometer)

CS con 0
CLK con 2
AD con 1
theData var Byte
halfDegree var Byte

DIRA=%0101
convert:
pause 1000
low CS ' Select ADC
theData = 0 ' Clear data
shiftin AD,CLK,MSBPOST,[noparse][[/noparse]theData\9] ' Get data
high CS ' Deselect ADC
halfDegree=theData.bit0
debug bin8 theData, " | "
theData=theData>>1
debug dec theData
if halfDegree=1 then pointFive
debug ".0° C",cr
goto convert

pointFive:
debug ".5° C",cr
goto convert

---

--- In basicstamps@y..., "Dennie Bishop" <dbishop@e...> wrote:
> Can you post a sample of the code?
>
>

---

Original Message

---

> From: special_4k4 [noparse][[/noparse]mailto:special_4k4@y...]
> Sent: Monday, January 07, 2002 10:48 PM
> To: basicstamps@y...
> Subject: [noparse][[/noparse]basicstamps] ADC08831 Help needed
>
> If anyone can help with sample programs using the ADC08831 Analog-
to-
> Digital IC, I would greatly appreciate it. I'm trying to get a
> reading from an LM35DT teperature sensor (10mV/degree C) and I'm
> having a little difficulty. When I do shiftin AD,CLK,MSBPOST,
> [noparse][[/noparse]theData] I seem to lose the last bit while adding an extra 0 bit at
> the beginning so I am doing shiftin AD,CLK,MSBPOST,[noparse][[/noparse]theData\9]. I'm
> not exactly sure what I am doing wrong (if anything) so any help
> would be GREATLY appreciated!
>
> -special [noparse][[/noparse]k]
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@y...
> 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/

Archiver

The ADC0831 does require that you shift in 9 bits, because the first
bit out is a "dummy" bit. With a 2.55 volt reference, the
resolution should be 1 degree C. (2.56 volt/256 = 0.10 volt) I
think that if you want 0.5 degree resolution, you need a 1.28 volt
reference.

If you do use a 1.28 volt reference, then the formula to display with
0.5 degree resolution can be simplified, using the data just as it
comes from the shiftin command:
theData = theData*5 ' each bit represents 0.5 degree
debug dec theData/10,".",dec1 theData,cr

-- regards,
Tracy Allen
electronically monitored ecosystems
mailto:tracy@e...
http://www.emesystems.com


>When I do shiftin AD,CLK,MSBPOST,
> > [noparse][[/noparse]theData] I seem to lose the last bit while adding an extra 0 bit at
> > the beginning so I am doing shiftin AD,CLK,MSBPOST,[noparse][[/noparse]theData\9]. I'm
> > not exactly sure what I am doing wrong (if anything)
>....
>This is what I am doing now to measure the temperature (in C):
>
>

---

>'LM35DT:
>'Pin 1->5V
>'Pin 2->GND
>'Pin 3->Pin 2 on ADC08831
>'
>'ADC08831:
>' Pin 0 1--U--8 5V
>'Pin 3 of LM35DT 2 7 Pin 2
>' GND 3 6 Pin 1
>' GND 4

---

5 Ref. Voltage (2.55V using
>potentiometer)
>
>CS con 0
>CLK con 2
>AD con 1
>theData var Byte
>halfDegree var Byte
>
>DIRA=%0101
>convert:
> pause 1000
> low CS ' Select ADC
> theData = 0 ' Clear data
> shiftin AD,CLK,MSBPOST,[noparse][[/noparse]theData\9] ' Get data
> high CS ' Deselect ADC
> halfDegree=theData.bit0
> debug bin8 theData, " | "
> theData=theData>>1
> debug dec theData
> if halfDegree=1 then pointFive
> debug ".0° C",cr
>goto convert
>
>pointFive:
> debug ".5° C",cr
>goto convert
>

---

Archiver

The problem that I'm facing, however, is that I get the correct
temperature only by shifting the data >>1. It seems like the last
bit is representing half a degree... I get the correct temperature
when I capture only the first 8 bits, but it maxes out at 127 (When I
connect the V+ on the ADC to the ref voltage, which SHOULD give me
255). When I connect the V+ on the ADC to the ref voltage and
capture 9 bits (dropping the first), I get all 255 bits of
resolution. I'm confused.

-special [noparse][[/noparse]k]

--- In basicstamps@y..., Tracy Allen <tracy@e...> wrote:
> The ADC0831 does require that you shift in 9 bits, because the
first
> bit out is a "dummy" bit. With a 2.55 volt reference, the
> resolution should be 1 degree C. (2.56 volt/256 = 0.10 volt) I
> think that if you want 0.5 degree resolution, you need a 1.28 volt
> reference.
>
> If you do use a 1.28 volt reference, then the formula to display
with
> 0.5 degree resolution can be simplified, using the data just as it
> comes from the shiftin command:
> theData = theData*5 ' each bit represents 0.5 degree
> debug dec theData/10,".",dec1 theData,cr
>
> -- regards,
> Tracy Allen
> electronically monitored ecosystems
> mailto:tracy@e...
> http://www.emesystems.com
>
>

Archiver

Turns out that I WAS using a 1.28V reference voltage (stupid me) and
that's what my problem was. I checked with my voltmeter today and
saw the voltage was so low with the potentiometer, so I fixed that
and it fixed my readings! Thanks for all the help [noparse]:)[/noparse]

-special [noparse][[/noparse]k]

--- In basicstamps@y..., Tracy Allen <tracy@e...> wrote:
> The ADC0831 does require that you shift in 9 bits, because the
first
> bit out is a "dummy" bit. With a 2.55 volt reference, the
> resolution should be 1 degree C. (2.56 volt/256 = 0.10 volt) I
> think that if you want 0.5 degree resolution, you need a 1.28 volt
> reference.
>
> If you do use a 1.28 volt reference, then the formula to display
with
> 0.5 degree resolution can be simplified, using the data just as it
> comes from the shiftin command:
> theData = theData*5 ' each bit represents 0.5 degree
> debug dec theData/10,".",dec1 theData,cr
>
> -- regards,
> Tracy Allen
> electronically monitored ecosystems
> mailto:tracy@e...
> http://www.emesystems.com
>
>