Amplifiers (and voltmeters)

I am working on this project where I plan to make an wall mounted weather panel, ocean temperature, air quality, UV index, whatever meter! Essentially, a bunch of voltmeters connected to the output pins of a microprocessor.
If I understand correctly, the output of my microprocessor (the arduino) is 0-5v. Most voltmeters I can find are made for cars, and range from 8-18v. Is there a way that I can amplify the PWM signal coming out of my microprocessor from 0-5v to 0-18v? Or do you know of a better way to accomplish what I am doing? Maybe a supplier of 0-5v gauges?


Go on over to Ebay, and in the Business and Industrial section, search on “panel meters”. See what’s cheap and etc. and note the various inputs. It’s been too long since I did electronics, but you should be able to drive various meters with an op amp or voltage divider/current shunt or whatever. Maybe you can get an old 0-1 milliamp meter out of something, or get one at Radio Shack cheap. Or maybe use something like this:

Maybe you can get one of the Harbor Freight digital voltmeters on sale for $2.99 and play around.

Here’s an article about interfacing an Arduino to a panel meter:

There are lost of other links there as well. Have fun

If I were going to do this project, I’d use one of the 161 or 20 1 LCD displays. The PIC chip has a serial port and these displays accept serial port imput. This would let you write:

Time 12:34 PM
Temp 72 F 22 C
Wind NNE 4 MPH
Rainfall 0.2 inch
and so on.

The LCD’s are super simple to write to and there are 100’s articles how to do it.

The displays are cheap, about $12-$20. You can get carried away and get the 4 line version and put all the data up at one time.

Digikey and other places carry them.

heh… However one of the purposes of this project was to make it look like an old barometer that people used to hang on their walls… I was going to customize the gauges with a backing suiting the information they display.
Thanks for all of the help!

And of all my luck, I can’t find that type of meter anywhere! I looked on amazon, froogle, etc… Nothing… Any links would be appreciated…

Many of the meters may be marked to show a certain value but the input value is something different. For example, some show the scale in pounds :smiley:

Here’s a really nice (new) old Weston 0-1 mA meter:

Just be advised that any analog (needle-type) meter can be made to display any range of voltage or current that you want.

All meter movements are essentially the same, using the D’arsonval movement. A typical meter may have a full scale sensitivity of 1 milliamp.

To convert this to a 0-5 volt voltmeter, you measure the raw voltage it takes to bring the meter to full scale. Let’s say it’s 1 volt (makes the math easier). You want to display 5 volts full scale. Using Ohm’s law V=I*R or V/I=R, we get 1/.001=1000 Ohms of internal resistance. So we put a 4000 Ohm resistance in series with the meter, 4/5 of the voltage is dropped by the resistor, 1/5 by the meter, so a 5 volt signal puts 1 volt on the meter for a full scale reading.

To use your automotive meter, open it up, pull out the existing resistor, measure the meter, and calculate a new resistor. (Automotive meters use a second resistance to set the bottom value, 8 volts for example. Write and I’ll explain it if you want)

To measure current, we do the same measurements on the meter, but now we put a smaller resistance across the meter, so most of the current goes through the shunt resistor and only a little through the meter. For example, for a 10 Amp fuss scale, we want 0.001/10 or .0001 (1/10000th) of the current to pass thru the meter, and 9999/10000th of the current to pass thru the resistor. in this case, an 0.1 Ohm resistance would make that meter read 10 Amps full scale. (A piece of 16 Ga wire serves as a decent shunt)

PM me if you don’t get something, I’m short on time tonight.


Just thought of somehting: A tiny servo motor would be able to display any angle using a PWM signal. Modern cars use tiny servo motors for the ‘analog’ gauges. Very cheap at a junkyard. Hmm, so are analog meter movements…


I have a few new old stock panel meters that I picked up years ago…I don’t think I’ve used any of them for anything. I wonder where they are? The only one that’s in the office here is a 4.5" rectangular Simpson, which measures 60 VDC full scale. (as Don mentioned, there’s gotta be a resistor in side that can be changed to make it read whatever you want)

going on a trip tomorrow, but if you can’t find anything in the next week, PM me and I’ll see if I can send you a meter or two.

Ahh so it’s more of a “steampunk” project than a digital weather station.

Cheap panel meters from Marlin P Jones Sales. His stock varies, but all he has right now are square ones. Call and he may have some others in smaller quantities. All Electronics has some interesting edge meters. Surplus Electronicsand the Surpls Sales of NE have been places to find other shapes and sizes.

Other resource would be a hamfest, you’ll find a variety of meters in different sizes and shapes. ARRL Hamfest locator will help with ham’s in your area.

I like the servo idea to move the indicator around. That way you could nest the pointers and make it exactly what you want the final product to look like.

Added bonus is the sound of the servo’s moving things around as it works.

Take a look at the bottom of the page for “Analog Milliamp Meter Used as Voltmeter”. It shows a milliamp meter being used as a voltmeter. This is what Don was talking about.

Also see:

And this is just pretty neat:

If you are in New York City, there should be a number of electronic/electrical junk places around. I used to see stuff like this in some of the surplus shops on Canal Street between Chinatown and Little Italy.

Another Sperry, $8.99 with shipping:

You might find that the cheapest way to get analog meter movements is to buy an entire voltmeter and gut it. For example, here’s a Sperry meter for $3.95. plus shipping. If you buy multiple units, there’s no extra shipping. Maybe you can buy one at Home Depot first to see if it is viable. It might be difficult or impossible to get the bezel off (intact) to put on your own scale.

Here’s another link to them:

Ehh, not any more, all those places are gone. Only a few were left 25 years ago, and in the meantime not one has survived.

There are a few surplus stores sprinkled around the country. I wish someone could compile them all, but most are only known locally. Skycraft Surplus in orlando is one, on Fairbanks at I-4. There’s also a place in New Hampshire, but I haven’t found it yet. (The state is bigger than it looks on a map). Maybe next kickoff I’ll go to Manchester and ask around.



If you’re expecting a true 0-5V swing on your PWM/DAC outputs, you’d be wise to use an op-amp to drive your gauges anyways. The sourcing/sinking current on the ATmega outputs drops fairly rapidly the closer you get to 0V or 5V. If you’re running onto an RC filter to get your nice analog voltage out, those nonlinear currents are going to play heck with your linearity. Plus you can use whatever filtering you want at that point.

Also, to Don:

In Houston, Electronic Parts Outlet (EPO) is a decent surplus store, and Ace Electronics is a decent part shop. So there’s definitely some good places left here and there.

I guess I’m dating myself a bit :smiley: I guess that was 1985-90 or thereabouts.