Basic question from a Real Beginner
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Posts: 46,084
Hi All,
Sorry if the question seems basic, but I was wondering if the Stamp can
compare voltages that appear on the input pins. I have an application that I
need to compare several voltages to choose the lowest voltage. The highest
the voltage reaches curently is 6 volts, but can easily be reduced. Is this
possible with the Stamp????
Thanx in advance for the help.
Mike
Sorry if the question seems basic, but I was wondering if the Stamp can
compare voltages that appear on the input pins. I have an application that I
need to compare several voltages to choose the lowest voltage. The highest
the voltage reaches curently is 6 volts, but can easily be reduced. Is this
possible with the Stamp????
Thanx in advance for the help.
Mike
Comments
On Mon, 17 Jul 2000 HQ54@A... wrote:
> Sorry if the question seems basic, but I was wondering if the Stamp can
> compare voltages that appear on the input pins. I have an application that I
> need to compare several voltages to choose the lowest voltage. The highest
> the voltage reaches curently is 6 volts, but can easily be reduced. Is this
> possible with the Stamp????
The Stamp does not contain an A-to-D converter, which is what you will
require. Consider using a pair of ADC0831 8-bit A-to-D converter chips,
or a single LTC1298 12-bit 2-port A-to-D converter chip.
Both of these chips interface easily to the BS2 using an I2C interface.
See the www.parallaxinc.com webpage for applicable Application Notes (with
example software). You can get these chips from Parallax for $5 - $10
respectively.
--- Jay
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3:00am up 67 days, 8:53, 6 users, load average: 0.29, 0.06, 0.02
Furthermore you could scale your voltage thru a resistor divider to fit
this value.
ACJacques
HQ54@A... wrote:
>
> Hi All,
>
> Sorry if the question seems basic, but I was wondering if the Stamp can
> compare voltages that appear on the input pins. I have an application that I
> need to compare several voltages to choose the lowest voltage. The highest
> the voltage reaches curently is 6 volts, but can easily be reduced. Is this
> possible with the Stamp????
>
> Thanx in advance for the help.
> Mike
> Sorry if the question seems basic, but I was wondering if the Stamp
can
> compare voltages that appear on the input pins. I have an application
that I
> need to compare several voltages to choose the lowest voltage. The
highest
> the voltage reaches curently is 6 volts, but can easily be reduced. Is
this
> possible with the Stamp????
Hi Mike,
The stamp's RCtime command can be used to measure and compare voltages
and to achieve approximately the same repeatability as an 8 bit A/D
converter. It might be simpler to use an A/D converter with multiple
inputs, but maybe not. RCtime does take a resistor and a capacitor for
each pin input. An addtional resistor (to Vdd) is required if the minimum
input volage will be less than 2 volts.
100k 220
unknown V --/\/\---o--/\/\-P0
>2V |
=== 0.068uf
|
Vss
dut var word
low 0
loop:
RCtime 0,0,dut
low 0
debug dec dut
goto loop
That will give values of about dut=280 at 18 volts input and dut=2900 at
2.5 volts input. So to find the maximum voltage, you step through your
channels and pick the one that shows the lowest dut value. To get the best
results, adjust the value of the 100kohm or the 0.068uF to give readings of
about 200 at the maximum expected input voltage, 6V in your case. The dut
reading will be "noisy" when the value of DUT is larger than 1000, so you
may have to do some filtering on it for the best accuracy at the lower
voltages. Wire your system to bring the ground leads for your unknown
voltages in very close to the Vss pin of the stamp, to avoid extra ground
loop noise.
-- Tracy Allen
Electronically Monitored Ecosystems
http://emesystems.com/BS2misc.htm#battery voltage & RCtime
-- Tracy Allen