How to measure current with Stamp
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Can anybody tell me how to setup a current (0-125ma) measuring
system with a Stamp2? Thanks.
system with a Stamp2? Thanks.
Comments
system with a Stamp2? Thanks.
Take the 125mA and pass it through a resistor. V=IR
If you use a 33 Ohm, this will give approximatly 0-4.125V, which you
can use an A/D to measure.
-Martin Hebel
Electronic Systems Technologies
Southern Illinois University
http://www.siu.edu/~imsasa/est
--- In basicstamps@yahoogroups.com, "John Schwab
<johnschwab5678@y...>" <johnschwab5678@y...> wrote:
> Can anybody tell me how to setup a current (0-125ma) measuring
> system with a Stamp2? Thanks.
Jameco, less than $1.00 output changes as the flux field around the
wire changes. very simple. or if you want even cheaper, wrap a few
dozen loops around your wire, and measure the induced signal !
Dave
--- In basicstamps@yahoogroups.com, "Martin Hebel <martin@s...>"
<martin@s...> wrote:
> Yes, convert it to a voltage! [noparse]:)[/noparse]
>
> Take the 125mA and pass it through a resistor. V=IR
>
> If you use a 33 Ohm, this will give approximatly 0-4.125V, which
you
> can use an A/D to measure.
>
> -Martin Hebel
> Electronic Systems Technologies
> Southern Illinois University
> http://www.siu.edu/~imsasa/est
>
>
> --- In basicstamps@yahoogroups.com, "John Schwab
> <johnschwab5678@y...>" <johnschwab5678@y...> wrote:
> > Can anybody tell me how to setup a current (0-125ma) measuring
> > system with a Stamp2? Thanks.
the induced current into the sensor. A DC one is usually a linear
hall effect device.
Though the original post did not specify, I am assuming this is a DC
level from some type of sensor?
-Martin
--- In basicstamps@yahoogroups.com, "Dave Mucha <davemucha@j...>"
<davemucha@j...> wrote:
> Use a current transformer.
> Jameco, less than $1.00 output changes as the flux field around the
> wire changes. very simple. or if you want even cheaper, wrap a
few
> dozen loops around your wire, and measure the induced signal !
>
> Dave
>
>
>
> --- In basicstamps@yahoogroups.com, "Martin Hebel <martin@s...>"
> <martin@s...> wrote:
> > Yes, convert it to a voltage! [noparse]:)[/noparse]
> >
> > Take the 125mA and pass it through a resistor. V=IR
> >
> > If you use a 33 Ohm, this will give approximatly 0-4.125V, which
> you
> > can use an A/D to measure.
> >
> > -Martin Hebel
> > Electronic Systems Technologies
> > Southern Illinois University
> > http://www.siu.edu/~imsasa/est
> >
> >
> > --- In basicstamps@yahoogroups.com, "John Schwab
> > <johnschwab5678@y...>" <johnschwab5678@y...> wrote:
> > > Can anybody tell me how to setup a current (0-125ma) measuring
> > > system with a Stamp2? Thanks.
--- In basicstamps@yahoogroups.com, "Martin Hebel <martin@s...>"
<martin@s...> wrote:
> Current transformers measure an AC signal, since that is what
causes
> the induced current into the sensor. A DC one is usually a linear
> hall effect device.
>
> Though the original post did not specify, I am assuming this is a
DC
> level from some type of sensor?
>
> -Martin
>
>
> --- In basicstamps@yahoogroups.com, "Dave Mucha <davemucha@j...>"
> <davemucha@j...> wrote:
> > Use a current transformer.
> > Jameco, less than $1.00 output changes as the flux field around
the
> > wire changes. very simple. or if you want even cheaper, wrap a
> few
> > dozen loops around your wire, and measure the induced signal !
> >
> > Dave
> >
> >
> >
> > --- In basicstamps@yahoogroups.com, "Martin Hebel <martin@s...>"
> > <martin@s...> wrote:
> > > Yes, convert it to a voltage! [noparse]:)[/noparse]
> > >
> > > Take the 125mA and pass it through a resistor. V=IR
> > >
> > > If you use a 33 Ohm, this will give approximatly 0-4.125V,
which
> > you
> > > can use an A/D to measure.
> > >
> > > -Martin Hebel
> > > Electronic Systems Technologies
> > > Southern Illinois University
> > > http://www.siu.edu/~imsasa/est
> > >
> > >
> > > --- In basicstamps@yahoogroups.com, "John Schwab
> > > <johnschwab5678@y...>" <johnschwab5678@y...> wrote:
> > > > Can anybody tell me how to setup a current (0-125ma)
measuring
> > > > system with a Stamp2? Thanks.
>Can anybody tell me how to setup a current (0-125ma) measuring
>system with a Stamp2? Thanks.
What about a 25 Ohm resistor in series with what you want to measure
and then just use an ADC to pick off the voltage across the resistor?
An 8-Bit ADC would give you approx 488uA resolution. A 12-Bit ADC
would give you approx 30uA resolution, but it might be difficult
distinguishing this against the noise floor.
>Can anybody tell me how to setup a current (0-125ma) measuring
>system with a Stamp2? Thanks.
Ahem!.. or better yet a 40 Ohm resistor... Sorry!
What about a 25 Ohm resistor in series with what you want to measure
and then just use an ADC to pick off the voltage across the resistor?
An 8-Bit ADC would give you approx 488uA resolution. A 12-Bit ADC
would give you approx 30uA resolution, but it might be difficult
distinguishing this against the noise floor.
> system with a Stamp2? Thanks.
John,
If you're wanting to measure AC then the CT (current transformer)
would be ideal, as the other guys on this list already mentioned.
If you're measuring DC then you can use the series resistor like a
few of the other guys talked about. However, seems like you need to
take a look at the load your driving before arbitrarily picking some
resistor value out of the air like 33 ohms, or 40 ohms or whatever.
If you add a series resistor to the circuit, the total resistance
will go up making the current go down. You'll also be dropping some
of your voltage across the resistor and you will have less voltage
across the load.
Say your load is 50 ohms and you have a 12V power supply connected to
it. Your total current will be .24A. Now you start adding a 33 ohm
resistor in series, your total current drops to .144A. You'll then
only have 7.2V across your original load. Depending on the nature of
the load this may not be acceptable.
Hope this helps
controls a light output. It outputs 12 Volts DC and varies the
current between 0-125ma. What I want to do is test the current
without any lights (so no load) hooked up to test if it is outputting
very little, some medium amount of current, or something close to
maximum (125ma) current. I need to make a harness to test this
circuit, and I already have a Stamp2BSX in the system, so I am hoping
to use it to check this too.
/John
--- In basicstamps@yahoogroups.com, "Ron Jeremy <ronjeremy912@h...>"
<ronjeremy912@h...> wrote:
> > Can anybody tell me how to setup a current (0-125ma) measuring
> > system with a Stamp2? Thanks.
>
> John,
>
> If you're wanting to measure AC then the CT (current transformer)
> would be ideal, as the other guys on this list already mentioned.
>
> If you're measuring DC then you can use the series resistor like a
> few of the other guys talked about. However, seems like you need
to
> take a look at the load your driving before arbitrarily picking
some
> resistor value out of the air like 33 ohms, or 40 ohms or
whatever.
> If you add a series resistor to the circuit, the total resistance
> will go up making the current go down. You'll also be dropping
some
> of your voltage across the resistor and you will have less voltage
> across the load.
>
> Say your load is 50 ohms and you have a 12V power supply connected
to
> it. Your total current will be .24A. Now you start adding a 33
ohm
> resistor in series, your total current drops to .144A. You'll then
> only have 7.2V across your original load. Depending on the nature
of
> the load this may not be acceptable.
>
> Hope this helps
You should probably load your circuit so you know it really can
output the 12 volts and 125 ma. 96 ohms (=12V/0.125A) is the right
load for that. If you split the load into 2 resistors, 56 ohms
between the sense point and the 12v input and then 40 ohms between
sense point and ground, the sense point will go from 0 to 5 volts as
the load current goes from 0 to 125 ma. (Likewise the input voltage
will go from 0 to 12 volts at the same time because of the 96 ohm
total load). The 0-5 volt sense point voltage can be measured many
ways depending on the accuracy you need. An A/D gives best accuracy
but there may be a circuit somewhere to measure that voltage range
using RCTIME and another resistor or two and a capacitor.
Harry
Stamp Robotics to the next level
www.bluebelldesign.com
--- In basicstamps@yahoogroups.com, "John Schwab
<johnschwab5678@y...>" <johnschwab5678@y...> wrote:
> Here is exactly what I am trying to do: I have a device that
> controls a light output. It outputs 12 Volts DC and varies the
> current between 0-125ma. What I want to do is test the current
> without any lights (so no load) hooked up to test if it is
outputting
> very little, some medium amount of current, or something close to
> maximum (125ma) current. I need to make a harness to test this
> circuit, and I already have a Stamp2BSX in the system, so I am
hoping
> to use it to check this too.
>
> /John
>
>
> --- In basicstamps@yahoogroups.com, "Ron Jeremy
<ronjeremy912@h...>"
> <ronjeremy912@h...> wrote:
> > > Can anybody tell me how to setup a current (0-125ma) measuring
> > > system with a Stamp2? Thanks.
> >
> > John,
> >
> > If you're wanting to measure AC then the CT (current transformer)
> > would be ideal, as the other guys on this list already
mentioned.
> >
> > If you're measuring DC then you can use the series resistor like
a
> > few of the other guys talked about. However, seems like you need
> to
> > take a look at the load your driving before arbitrarily picking
> some
> > resistor value out of the air like 33 ohms, or 40 ohms or
> whatever.
> > If you add a series resistor to the circuit, the total resistance
> > will go up making the current go down. You'll also be dropping
> some
> > of your voltage across the resistor and you will have less
voltage
> > across the load.
> >
> > Say your load is 50 ohms and you have a 12V power supply
connected
> to
> > it. Your total current will be .24A. Now you start adding a 33
> ohm
> > resistor in series, your total current drops to .144A. You'll
then
> > only have 7.2V across your original load. Depending on the
nature
> of
> > the load this may not be acceptable.
> >
> > Hope this helps