Simple A to D

TechnoRobbo

This is a real simple A to D made from a Radio Shack Quad Comparator compatible to the LM339 and a BS2.

It uses an PWM command and RC circuit to create the reference voltage and a short and very fast successive approximation routine to read the input voltage. The result is very linear yielding a value from 0 (0v)·to 255 (5V).


the schematics and code are attached below.


' {$STAMP BS2}
' {$PBASIC 2.5}
IDX······ VAR Nib
X········ VAR Byte
LOW 7
INPUT 15
Main:···· 'Successive Aproximation Routine
DO
··· x=128
··· FOR idx=7 TO 0
····· X=X | DCD idx
····· PWM 7, X, 5
····· IF IN15=0 THEN
········ X=X ^ DCD idx
····· ENDIF
··· NEXT
··· DEBUG HOME,DEC3 X
LOOP
END
·····

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Have Fun


TR

Post Edited (TechnoRobbo) : 12/30/2006 4:29:45 PM GMT

TechnoRobbo

Found this article in nuts and volts - code is not as tight but the circuit draws less amps.

http://www.parallax.com/dl/docs/cols/nv/vol1/col/nv25.pdf

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Have Fun


TR

TechnoRobbo

Increasing the Resolution

Utilizing the other comparators on the chip you can increase the A/D resolution by using pull up and pulldown resistors in voltage dividing combinations - In the example below on comparator handles 0v to 2.5v and the other handles 2.5v to 5v.· I sum them together to double the resolution. This allows the stamp to read 1/100th of a volt (9 bit resolution). Sometimes the range of the sensor your using is to large and impractical -Using this technique to·adjust the your A/D reference voltage may yield even higher resolutions without the need for more pins or components.

' {$STAMP BS2}
' {$PBASIC 2.5}
IDX······ VAR Nib
X········ VAR Byte
stdout··· VAR Word
INPUT 15
INPUT 14
Main:···· 'Successive Aproximation Routine
DO
··· x=0
··· FOR idx=7 TO 0
····· X=X | DCD idx
····· PWM 7, X, 5
····· IF IN15=0 THEN
········ X=X ^ DCD idx
····· ENDIF
··· NEXT
··· stdout=x
··· 'double it
··· x=0
··· FOR idx=7 TO 0
····· X=X | DCD idx
····· PWM 6, X, 5
····· IF IN14=0 THEN
········ X=X ^ DCD idx
····· ENDIF
··· NEXT
··· stdout=stdout + x
··· DEBUG HOME,DEC3 stdout
LOOP
EN


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Have Fun


TR

Post Edited (TechnoRobbo) : 1/2/2007 3:51:59 AM GMT

sam_sam_sam

TechnoRobbo


Utilizing the other comparators on the chip you can increase the A/D resolution by using pull up and pulldown resistors in voltage dividing combinations


Can you give some·more details on how to do this what is in red

What i would like to do is have the following

comparator 1······· ·0 to 5 volts
comparator 2·········5 to 10 volts···· Any· ··s

comparator 3········ 10 to 15 volts


Please tell me if this can be done and how you go about doing this

·Have tried this part of what i am talking about before

Thank You for any ··that you have on how to do this

Sam

TechnoRobbo

Divide your input voltage with 3· resistor·10k like this - rest of cicuit is attached

use PWM 7, X, 10· instead of PWM 7, X, 5 (replace 7 with the pin your using)

·················






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TR

Post Edited (TechnoRobbo) : 1/5/2007 2:14:37 PM GMT

TechnoRobbo

sorry I had to repost the schematic I forgot the pullup on pin 13

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TR

sam_sam_sam

TechnoRobbo

Thanks for your post and your ·
·If I have time this weeken I will· built this and try it and let you how it works

I just want to make sure of one thing and that is that all "vdd"'s are 5 volts

Please let know if I sm right about this

Thank again for help and you time






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··Thanks for any··that you may have and all of your time finding them





Sam

TechnoRobbo

Yes Vdd's are 5volts but the Vin (pin 3 on comparator) must be more than 5 volts to resolve 5 volts.

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TR

sam_sam_sam

TechnoRobbo

Thanks for your reply

Thanks for telling about pin 3 on the LM339 and all of the VDD"s




·I will try to have some fun··········· ·· ·But these Guys are having way to much fun



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··Thanks for any··that you may have and all of your time finding them





Sam

sam_sam_sam

TechnoRobbo

How would you write the code for pins 13 and pin 5

' {$STAMP BS2}
' {$PBASIC 2.5}
IDX VAR Nib
X VAR Byte
stdout VAR Word
INPUT 15
INPUT 14
INPUT 13
Main: 'Successive Aproximation Routine
DO
x=0
FOR idx=7 TO 0
X=X | DCD idx
PWM 7, X, 5
IF IN15=0 THEN
X=X ^ DCD idx
ENDIF
NEXT
stdout=x··········· · '........................................
'double it
x=0

FOR idx=7 TO 0
X=X | DCD idx
PWM 6, X, 5
IF IN14=0 THEN
X=X ^ DCD idx
ENDIF
NEXT

' I am not sure what·is suppost to be here·...........>>>>>>>>

This

'stdout=stdout + x·········· ·'.......................................

·Or this

My thinking is that this is what go here

'stdout=x
'double it
'x=0
·
FOR idx=7 TO 0
X=X | DCD idx
PWM 5, X, 5
IF IN13=0 THEN
X=X ^ DCD idx
ENDIF
NEXT
stdout=stdout + x ......................................' Is this right
DEBUG HOME,DEC3 stdout
LOOP

LOOP
END

Thanks for all of the help and that·you given to me in this matter



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··Thanks for any··that you may have and all of your time finding them





Sam

Post Edited (sam_sam_sam) : 1/10/2007 3:03:45 AM GMT

TechnoRobbo

Add low then middle then high , use a duration of 10 due to highest resistance in voltage path. The stages will max out at 255 before the next stage rises from 0. The output is·cumulative therefore the range will be 0 to about 765 (0V to 15V). All 4 comparators together·will give you a 10 bit resolution but it uses up 8 Stamp IO pins.

·

' {$STAMP BS2}
' {$PBASIC 2.5}
IDX VAR Nib
X VAR Byte
stdout VAR Word
INPUT 15
INPUT 14
INPUT 13
Main: 'Successive Aproximation Routine
DO
x=0
FOR idx=7 TO 0
X=X | DCD idx
PWM 7, X,10
IF IN15=0 THEN
X=X ^ DCD idx
ENDIF
NEXT

stdout=x·············

x=0
·
FOR idx=7 TO 0
X=X | DCD idx
PWM 5, X, 10

IF IN13=0 THEN
X=X ^ DCD idx
ENDIF
NEXT
stdout=stdout + x

x=0

FOR idx=7 TO 0
X=X | DCD idx
PWM 6, X, 10
IF IN14=0 THEN
X=X ^ DCD idx
ENDIF
NEXT

stdout=stdout + x··········



DEBUG HOME,DEC5 stdout
LOOP

END






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Have Fun


TR

Post Edited (TechnoRobbo) : 1/27/2007 4:44:53 AM GMT

sam_sam_sam

TechnoRobbo
Thanks so very much reply this will help alot

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··Thanks for any··that you may have and all of your time finding them

·
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·
·
Sam

sam_sam_sam

TechnoRobbo

Here is the code for the Battery Tester

For some reason the Attachment Manager is not working very good to night





I put this together today the Simple A to D·this works very good thanks for posting it··I have not built the other one yet· but i will when i have some more time

·this what i came up with a battery tester and this is the little routine that i wrote for it

I will need use this routine when i built a project that i have in mind builting

· 'This Routine Displays The type of battery that is hook up

I add this to your routine



··· IF x > 50 AND x < 80 THEN
··· DEBUG "1.2 TO 1.5 Volts", CR
··· PAUSE 500···················· 'This is to clear the screen·· I am going to put leds instead of the debug statements this just to test it
··· EXIT

··· ELSEIF x > 120 AND x < 160 THEN
··· DEBUG " 2.5 TO 3.0 Volts", CR
··· PAUSE 500····················· 'This is to clear the screen
··· EXIT

··· ELSEIF x = 238 THEN
··· DEBUG "4.5 Volts", CR······· ' The range is N/A at this time will come latter
··· PAUSE 500························ ·'This is to clear the screen
··· EXIT

··· ENDIF


LOOP

DEBUG CLS, CR····················· 'This is the routine to clear screen
GOTO main




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··Thanks for any··that you may have and all of your time finding them

·
·
·
·
Sam

Post Edited (sam_sam_sam) : 1/16/2007 3:59:49 AM GMT

TechnoRobbo

Glad I could help.

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Have Fun


TR

darshanrt

Hey Guys,


I am going thorugh your conversations and I'm really amazed by your work... I have some similar question to continue if you guys can help me too... well suppose I have a battery outside and if I want to measure its voltage with the use of basic stamp, how can I go with it...??

again appriciated,

Regards,
Darshan

TechnoRobbo

from Private message:

a 12 bit A to D will give you 0 to 5 volt with 4096 step resolution
multiply your input x and multiply by */3125
volt=x*/3125
5 volts will read out as 49987
use the DIG command to format the output and add the decimal point
DEBUG DEC1 x DIG 4,".",DEC1 x DIG 3,DEC1 x DIG 2,DEC1 x DIG 1,DEC1 x DIG 0

http://www.parallax.com/detail.asp?product_id=604-00026

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Have Fun


TR

Luiz mauricio mion

The ne566 vco , works like a time lapsed A/D conversion,count the number of cycles square wave,and pre determine the amount of cycles to count.
I do not remenber how much speed this VCO work,but its good to obtain voltage meter or low sample rate audio,sampling.

po2le

Techno,

I've built and used the simple A to D converter using an LM 339, it works.· Thanks for the information.

Can I store the results of the A to D output in EEprom?· The results are shown as numbers up to 255, which indicates 5v, on the debug screen.· Can these results be stored as the same numbers in EEPROM?

Thanks

Patrick

Mike Green

po2le,
Read the Stamp Basic Manual sections on the WRITE, READ, and DATA statements to learn about the use of EEPROM for data storage.