Digital Voltage Meter For your Car......

Janitor Tzap · Post by **Janitor Tzap** » Sat Sep 13, 2008 8:54 am

There was an article in Nuts&Volts about adding a Digital Volt Meter to your car.
Well, now that DMM's are cheaper than a 4 digit digital panel volt meter.
{$6.96 from DesignNotes.com, $7.50 from Electronix Express.}
I was thinking of using the DMM instead of the panel meter.

Any one remember what issue of Nuts&Volts that was?

Signed: Janitor Tzap

MrAl · Post by **MrAl** » Sat Sep 13, 2008 9:45 am

Hi Janitor,

Just to note, although many DVM's are cheap they also run on batteries.
They are not all powered the same way either. Some are powered with
a battery that has to be 'floating' with respect to the ground of the test
lead so that you can not use the power from the auto (12v) and a small
regulator to power the meter.
Other meters, however, are powered with a battery that does connect
to the same ground as the test ground lead. This allows connecting
to the battery with a small regulator ic chip to power the meter when
the car is running or ACC switch activated.

Im not sure how to tell them apart anymore. The panel meters you
can buy for 7 dollars (USD) sometimes tell you up front if the meter
can be powered from a battery that shares ground with the test lead
input ground. It would probably be a good idea to get one of these.
If you get a regular DVM you may have to power it with a battery
which means you will have to turn it on and off everything you start or
turn off the car, unless of course you plan on adding a relay or
transistor to turn the power to the meter on (via battery) every time
you start the car. The drawback though is that the battery will be
draining whenever the car is running.

jwax · Post by **jwax** » Sat Sep 13, 2008 3:36 pm

Chances are, you could build one for less than this...
http://www.jcwhitney.com/CYBERDYNE-PLUG ... _10114.jcw

Janitor Tzap · Post by **Janitor Tzap** » Sat Sep 13, 2008 6:25 pm

Hmm........

I found that DigiKey carries one also for even cheaper than the one you have listed from JC Whitney jwax.
http://dkc3.digikey.com/PDF/T083/2486-2487.pdf

I'd still would like to find that article.
Just to see what all I would need.
And the totaling up the cost of building it, than buying a already manufactured unit.

Thanks thou!

Signed: Janitor Tzap

MrAl · Post by **MrAl** » Sun Sep 14, 2008 6:13 am

Hi again,

WOW, they are high priced! Check out AllElectronics or Jameco or
something like that, as some places like this typically have them for
12 dollars (USD) or less.

Janitor Tzap · Post by **Janitor Tzap** » Tue Sep 16, 2008 11:27 am

Thank you for that info MrAl.

Jameco doesn't carry any self-powered meters.

But AllElectronics carries one for $15.

But, I still would like to find that article.

Thanks.

Signed: Janitor Tzap

jollyrgr · Post by **jollyrgr** » Tue Sep 16, 2008 2:38 pm

I do not recall the project you are referring to. I do recall a tachometer project and an RC battery monitor.

I normally would use my battery powered multimeters to test automotive problems. I have a plug that goes into the accessory (cigarrette lighter) and is used for ham/CB radio. It has banana jacks on it and can be found at Radio Shack (Model: 270-1521). I put the probes in the jacks and monitor the battery and/or alternator voltages. This works great for any electronics test meter.

But for $14 at Walmart I finally bought a meter that monitors the battery, is self powered right from the lighter plug, is back lit, and also displays logos for BATTERY only and ALTERNATOR. It is similar to this one:

http://www.bhphotovideo.com/c/product/1 ... _with.html

I cannot find the one I got at Walmart online. But it is a very nice tool to have. I have several meters ranging from multiple Radio Shack hand helds, clamp on amp/multimeters, Fluke bench meters and so on. Monitoring battery and alternator function is easy enough to do using these meters and a break out plug. But I figured for the price the Walmart automotive dedicated meter was well worth it as it avoids the headache of batteries for the multimeters or building an isolation circuit.

Janitor Tzap · Post by **Janitor Tzap** » Tue Sep 16, 2008 9:31 pm

jollyrgr wrote:I do not recall the project you are referring to. I do recall a tachometer project and an RC battery monitor.

I normally would use my battery powered multimeters to test automotive problems. I have a plug that goes into the accessory (cigarrette lighter) and is used for ham/CB radio. It has banana jacks on it and can be found at Radio Shack (Model: 270-1521). I put the probes in the jacks and monitor the battery and/or alternator voltages. This works great for any electronics test meter.

But for $14 at Walmart I finally bought a meter that monitors the battery, is self powered right from the lighter plug, is back lit, and also displays logos for BATTERY only and ALTERNATOR. It is similar to this one:

http://www.bhphotovideo.com/c/product/1 ... _with.html

I cannot find the one I got at Walmart online. But it is a very nice tool to have. I have several meters ranging from multiple Radio Shack hand helds, clamp on amp/multimeters, Fluke bench meters and so on. Monitoring battery and alternator function is easy enough to do using these meters and a break out plug. But I figured for the price the Walmart automotive dedicated meter was well worth it as it avoids the headache of batteries for the multimeters or building an isolation circuit.

Hmm.....
I looked on Walmart as well.
Nothing.

Well If these Unit's are only $15.00, and I can get them locally.
It would probably cost less than trying to modify a DMM.

I want to use them on 2 boats.
Put one in the console of a Pontoon boat.
I'd set it up with a momentary push button on switch, so your not draining the battery all the time.

The other to monitor the two batteries in a 14 footer Bass boat.
The main battery that runs the lights, pumps, and depth finder.
The second battery for the Trolling Motor.
I'd set it up on the Bass boat with a three way toggle switch with a center off.

Well, I'll keep looking for now.

Thanks jollyrgr.

Signed: Janitor Tzap

Craig · Post by **Craig** » Wed Sep 17, 2008 6:34 am

Hi,

I think the article that you're looking for is called "Self Powered Digital Voltmeter", with the tagline "Build a Nive Add-On for Your Car or Truck and LEarn a New Opamp Trick". It was written by Fernando Garcia and is on page 52 of the July 2004 issue.

I can send you a copy of it if you like.

Craig

Janitor Tzap · Post by **Janitor Tzap** » Wed Sep 17, 2008 6:56 am

Craig wrote:Hi,

I think the article that you're looking for is called "Self Powered Digital Voltmeter", with the tagline "Build a Nive Add-On for Your Car or Truck and LEarn a New Opamp Trick". It was written by Fernando Garcia and is on page 52 of the July 2004 issue.

I can send you a copy of it if you like.

Craig

No need too Graig.
I've got the 2004 Nuts&Volts CD.
I just thought the article was in one of the newer issues.

Thanks!

Update:Yes, that is the article that I was looking for Graig.

After looking through the components, prices, and shipping costs.
It is cheaper to just get the $15.00 units, than building one.

Thanks for all the help everyone.

Signed: Janitor Tzap

MrAl · Post by **MrAl** » Wed Sep 17, 2008 1:27 pm

Hi again Janitor,

I just checked the ones at AllElectronics and it looks like they both
require separate power supplies. I dont know if you can use this or
not. I thought they had at least one where you could use the same
power to power the meter as what is being measured.
The problem is, you can not connect these to +12v of a car and
measure the +12v battery too.

Im sure i saw other meters for about the same price on the web
at a popular site so if you cant find any others i'll do some searching.

reloadron · Post by **reloadron** » Wed Sep 17, 2008 2:27 pm

Years ago I did that using a panel meter just like this:

http://www.allelectronics.com/make-a-st ... V/-/1.html

I literally taped a 7805 and a cap to the back of it to power it, it shared a common gnd so it could measure its own voltage. I think I placed a simple pot accross the input to serve as a divider and calibrated it. The resolution was .1 Volt.

That little meter outlived the old '78 Bonniville it was in. Total cost is under 20 bucks.

<EDIT> Oh yeah, mounting was done with Velcro! </EDIT>

Ron

MrAl · Post by **MrAl** » Wed Sep 17, 2008 3:04 pm

There it is!! ha ha. That meter can monitor it's own power supply because
it can share ground with it.

Janitor Tzap · Post by **Janitor Tzap** » Wed Sep 17, 2008 6:59 pm

Yes, I saw that meter at Allelectronics as well, it's $15.

But, if those units that jolly showed me are available at say NAPA, or some other local auto parts store.

I think I'll check there first.

Thanks for the help!

Signed: Janitor Tzap

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Digital Voltage Meter For your Car......

Digital Voltage Meter For your Car......

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