Need help .

[Endy]

Hey gang.
New to this site, looking for advice.
I've got an old volt meter from hikok that was made specifically for Packard auto. Both names appear on the volt meter. I would like to design a circuit powered by a 12v battery that would make the voltage spike or pulse making the needle pulse. It's a 6-20 volt meter, so the existing resistor (providing it works) should be sufficient. How do I get the voltage to fluctuate the meter ?

Bonus question, I have some other meters that measure greater voltages that I would like to do the same to. Given that they are old devices, I want to wire them to operate of of s 12 volt DC battery as well.
In these cases is it just as simple as replacing the existing resistor with one suited for a 12 volt DC circuit to make the needle move ?

Any ideas, names of products, or sage advice appreciated.

Thanks.

 

[spec]

Hy Endy,

Welcome to ETO.

I see from your profile that you are in the United States. Care to tell us which state and put your location in your identity window on the left so we can instantly see where you are from without having to check your profile. This information is not only interesting but it also helps us to know what component vendors you can deal with and also to know about mains supplies, safety standards, etc (don't include your exact address though).

I take it that by 'hikok' you mean 'Hickok Electrical Instrument Company'. http://www.stevenjohnson.com/hickok/history.htm

To answer your question- yes a simple circuit can be designed to pulse your meters and there are many members on ETO who would be able to post a suitable schematic.

First though, we would need to know how much current your meters take for a full scale reading: just measure the DC current going into the meter at any reading and post a list giving meter reading against current. The reason why this information is required is that some meters, especially car (automobile) types, are hot wire and take a high current which a timer circuit would need to supply. As hot wire meters operate very slowly they may not move as fast as you would like.

You are correct that to change the voltage sensitivity of a meter you would change the series resistor.

My feeling is that an LM555 timer chip will make a good basis for a circuit to meet your requirements. http://www.ti.com/lit/ds/symlink/lm555.pdf
Many manufacturers make the 555 timer, as it is generally known, but in practical terms they are all the same. http://en.wikipedia.org/wiki/555_timer_IC There is also a CMOS version (LMC555) which is probably not ideal for your application.

Alternatively, if you didn't want to build a circuit yourself, a wide range of 555 based modules are available quite cheaply, especially on eBay. As these modules invariably have a relay fitted there should be no problem driving any meter, within reason that is. By the way, you may hear a slight click as the relay operates. http://www.ebay.com/sch/i.html?_odkw=timers+555&_osacat=293&_from=R40&_trksid=p2045573.m570.l1313.TR6.TRC2.A0.H0.Xtimer+555.TRS0&_nkw=timer+555&_sacat=293

Velleman products are particularly good; they make a range of timer modules: **broken link removed**

spec

 

[shortbus=]

If it has a Packard car logo, it may be worth some money to a collector. Before "messing it up" I'd join one of the Packard collector forums and see how much it's worth. Some old Ford branded tools are real collectable and pricey. And Packard stuff even more so, due to the rarity.

If it is a Packard Electric item (I worked for them for 30 years) it won't be as rare or worth as much.