Subject:
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Re: HB's analog inputs
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Wed, 26 Aug 1998 13:48:53 GMT
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Original-From:
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Dan White <dwhite@cybermetrix.=AvoidSpam=com>
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Reply-To:
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dwhite@^ihatespam^cybermetrix.com
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Viewed:
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1072 times
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edmund wrote:
>
> does anyone know if the handy board's analog inputs can accept analog
> current output(4-20mA) from a photo-electric distance sensor? (e.g. the
> sensor might return 4mA if the object is 1 ft away and 15mA if it's 3 ft
> away) or can it only accept analog voltage output(0-5V).
>
> if the function 'int analog()' is used and the analog input is 2.5V, would
> the handy-board return a value of 127? i believe the range of values is
> from 0-255 for 0-5V. what if the analog input is current?
>
> the distance sensor i'm going to buy comes with either a current or a
> voltage output and i don't know which will suit the HB best. can anyone
> help? thanks in advance.
>
> edmund
Edmund,
Typically the solution is to pass the 4-20 mA through a 250 ohm resistor
and measure the voltage across that resistor. As long as your A/D input
impedance is high, it can be ignored. A resistor is essentially a
current to voltage converter after all. You can use a 1% tolerance for
better accuracy. Keep in mind that you will never read zero because your
current never goes to zero. At 4 mA you will read one volt and at 20 mA
you will read 5 volt so now you have a 1-5 V transducer.
4-20mA ---------.----------- A/D +input
/
\ 250
/ ohm
\
4-20mA return---.----------- A/D -input (ground)
Good Luck,
Dan
--
/***********************************************************
* Dan White - National Instruments Certified Instructor *
* CyberMetrix,Inc. - National Instruments Alliance Member *
* <http://www.cybermetrix.com/ni> *
* dwhite@cybermetrix.com *
***********************************************************/
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Message is in Reply To:
 | | HB's analog inputs
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| does anyone know if the handy board's analog inputs can accept analog current output(4-20mA) from a photo-electric distance sensor? (e.g. the sensor might return 4mA if the object is 1 ft away and 15mA if it's 3 ft away) or can it only accept (...) (26 years ago, 26-Aug-98, to lugnet.robotics.handyboard)
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