Subject:
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Re: voltage/current monitors
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Tue, 4 Jun 1996 23:46:12 GMT
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Original-From:
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Chuck McManis <cmcmanis@netcom.com+nomorespam+>
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Viewed:
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1751 times
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Jeff Keyzer wrote:
> I'm interested in building a voltage monitor circuit for my robot's
> 6V battery, and a current monitor circuit for the motors. Is there
> an easy way to do this, with reasonable accuracy? I'd like to
> interface both of them to the analog sensors on the handy board.
Use a voltage divider (two resistors) to map the battery voltage to
a 0 - 5v signal for the A/D converter.
Depending on how much current your motors draw, you can put a .1 ohm
precision resistor in series with the motor and measure the voltage
drop across it. The voltage is equal to current * resistance so a
1amp current will create a .1v voltage drop, 5 amps appears as a .5v
voltage. Use an amplifier with a gain of 10 (any opamp can be used
for this) and that will convert a 1 - 5 amp current into a 1 - 5v
output.
Better solutions are to use one of the battery "gauge" ICs which
track the current flowing out of a battery to predict its current
capacity. These are made by Microchip, Maxim, and others. They are
used in laptops and portable electronics. They are better than a
voltage divider, especially for NiCds because the voltage output of
NiCds are nonlinear with discharge.
For the motor solution there are current sensors that simply wrap
a coil of wire around the motor supply lines. They then track the
changes in current as changes in voltage potential on the coil.
A bit more instrumentation but they avoid the resistor implementation
which tends to dissipate power on the order if I^2R or (.25 watts at
5 amps for a .1ohm resistor, 5 watts for a 1 ohm resistor)
--
Chuck McManis http://www.professionals.com/~cmcmanis
Director System Software, FreeGate Corp. cmcmanis@netcom.com
All opinions in the non-included text above are those of the author and
not of his employer or avocado plant.
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Message is in Reply To:
 | | voltage/current monitors
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| I'm interested in building a voltage monitor circuit for my robot's 6V battery, and a current monitor circuit for the motors. Is there an easy way to do this, with reasonable accuracy? I'd like to interface both of them to the analog sensors on the (...) (28 years ago, 4-Jun-96, to lugnet.robotics.handyboard)
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