Voltage and Current Measurement + Digital Pot.

Archiver

Hello,

I am working on a LCD display for voltage and current for a Car-Audio
project. My question is are there any modules out there that would
make this task easy? Or am I stuck using a regular ADC convertor with
a voltage divider to bring the voltage into the 5V range? Is using a
voltage divider the way one would normally measure a higher voltage?

For the current measurement, I can use one of the amploc sensors.
(http://www.amploc.com). Has anyone had experience with these?


Also, there is a control on one of the amplifiers which is just a
simple wired pot. I would like to incorporate this control into the
LCD display. I plan on using a xicor digital pot. The xicor unit will
exactly duplicate a mechanical pot, correct?

Thanks for any help.

-jr

Archiver

>I am working on a LCD display for voltage and current for a Car-Audio
>project. My question is are there any modules out there that would
>make this task easy? Or am I stuck using a regular ADC convertor with
>a voltage divider to bring the voltage into the 5V range? Is using a
>voltage divider the way one would normally measure a higher voltage?

If you want to do it on the cheap, you can use the RCtime command in the
Stamp. It requires a resistor and a capacitor. For the current you could
use something like the MAX471, which is a current monitoring IC from Maxim.
It too can be interfaced to the Stamp using the RCtime command. I am
assuming you are monitoring the power supply (battery) volage, not the
audio output voltage and current?

>control on one of the amplifiers which is just a
>simple wired pot..... I plan on using a xicor digital pot.
>The xicor unit will
>exactly duplicate a mechanical pot, correct?

You will have to be careful of the voltage ratings, especially if the
system you want to control runs on a different power supply. I think the
Xicor limit is something like 7 volts.

-- Tracy Allen
Electroncally Monitored Ecosystems
http://www.emesystems.com

Archiver

--- In basicstamps@egroups.com, Tracy Allen <emesys@c...> wrote:
> >I am working on a LCD display for voltage and current for a Car-
Audio
> >project. My question is are there any modules out there that would
> >make this task easy? Or am I stuck using a regular ADC convertor
with
> >a voltage divider to bring the voltage into the 5V range? Is using
a
> >voltage divider the way one would normally measure a higher
voltage?
> If you want to do it on the cheap, you can use the RCtime command
in the
> Stamp. It requires a resistor and a capacitor. For the current
you could
> use something like the MAX471, which is a current monitoring IC
from Maxim.

Tracy -- thanks for the reply.. .

I'll have to check out the RCtime command, I've seen it but never
actually used it. But, I don't mind the $$$ and think that using an
ADC would be a little more precise and cleaner. Are there any ADCs
which will accept a wider voltage range ie 10-20v? Or is it normal
practice to just use some 1% resistors to cut the voltage to the 0-5v
range?

I'll have to check out that maxim chip. The amploc device just clips
right over the wire and provides a voltage output which is related to
the current. Seems like a neat device. Need to order a few and see
what they are like...

> It too can be interfaced to the Stamp using the RCtime command. I
am
> assuming you are monitoring the power supply (battery) volage, not
the
> audio output voltage and current?

Yes, it is looking at the voltage and current on the input side of
the amp. (power supply side). It will also be monitoring temperature
of the amp. I plan on using a LM34 Percision temperature sensor
and another ADC to measure the voltage from the sensor.
What type of ADC should I be using for these "general" types of
measurement? I know a bunch of companies make ADCs. I think to
simplify things, it would be best to have an internal vref to
eliminate the external POT. Any recommendations on brand or model?

I suppose I could use a multi-channel one.. Would that be a bad idea?

> >control on one of the amplifiers which is just a
> >simple wired pot..... I plan on using a xicor digital pot.
> >The xicor unit will
> >exactly duplicate a mechanical pot, correct?
>
> You will have to be careful of the voltage ratings, especially if
the
> system you want to control runs on a different power supply. I
think the
> Xicor limit is something like 7 volts.

I'll have to look at this once I get the amp in my hands.

-jr

Archiver

> Are there any ADCs which will accept a wider voltage range
> ie 10-20v? Or is it normal practice to just use some 1%
> resistors to cut the voltage to the 0-5v range?

The resistor approach is is a good bet.

> The amploc device
> just clips right over the wire and provides a voltage
> output which is related to the current. Seems like a neat
> device. Need to order a few and see what they are like...

http://www.amploc.com -- looks interesting. I haven't ever tried them
either.
It looks like they generate about 40 millivolts per amp. So with a 12 bit
ADC that gives about 25 milliamps per bit. More sensitivity would require
an amplifier for the signal, but that might be pushing the 0.8% accuracy
specifications.

>It will also be monitoring temperature
>of the amp. I plan on using a LM34 Percision temperature sensor
>and another ADC to measure the voltage from the sensor.
>What type of ADC should I be using for these "general" types of
>measurement? I know a bunch of companies make ADCs. I think to
>simplify things, it would be best to have an internal vref to
>eliminate the external POT. Any recommendations on brand or model?
>I suppose I could use a multi-channel one.. Would that be a bad idea?

A multichannel one makes sense, given that you are already up to three
variables. The 2-channel LT1298 and the 8-channel MAX186 are popular here,
with info readily available about how to connect them to the Stamp. My own
favorite is the 11-channel TLC2543. Most of them have the option to use
the Vdd power supply as the reference.

-- Tracy Allen
Electronically Monitored Ecosystems
http://www.emesystems.com