What is the smallest voltmeter?

Less than 1" wide:

Standard 200mV FSD, just make your own input scaler.

Dave :)

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Expensive little guy isn't it? My battery pack (12 C-cells) exceeds its [14VDC] voltage rating.

BTW, I'm also building a Pulse Width Modulation circuit so I don't fry my 12VDC lightbulbs. This voltmeter will monitor its input and output voltage.

Bruce,

If you need to do voltage monitoring and PWM at the same time, I might recommend a AVR for the whole job. There might be cheaper/better/faster ways to do it, but you can get AVR microcontrollers for a few bucks that have PWM and ADC right on them. Use the ADC and a little resistor voltage divider to monitor your power. All the software development tools for AVRs are free, and you can build a programmer for them out of a parallel printer cable and a pair of wire cutters :)

You may be completely familiar with AVRs and microcontrollers, but if not, feel free to drop me a line at snipped-for-privacy@vonnieda.org if you want some tips.

Jason

Here is the smallest I have used, from Digikey:

Pretty spendy, though. You would have to scale the voltage down with a voltage divider.

you got to be kidding me, the price will kill the budget before you even get started.

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What's your time worth? If it's worth nothing to you then yes, it's expensive, otherwise it's not so expensive. You might be able to get it cheaper elsewhere.

No problem, drop the voltage with a regulator

Dave :)

The OP did not specify any budget. He asked for the smallest panel mount LCD voltmeter. If that's the best available then he might just have to pay that.

Dave :)

Well, you might be able to use LEDs of different colors, or a small seven segment LED (or LCD) to indicate one of 10 voltage levels. Add an led to the display to get 20 levels.

But without more information on your constraints and objective function, we're just playing bring me a rock.

Chuck

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Of course, one can make a tradeoff. Go bigger, and the selection goes up and the prices drop. Low end DMMs have become so cheap that using one as a dedicated meter is not outrageous. But then, the original poster wants small.

Or get a cheap analog panel meter, even one of those surplus "tuning meters" that have a calibration that doesn't mean a thing. Make the scale. Put a zener diode in series to get expanded scale, so it reads the range you want.

The poster can figure out what they really need the meter for, and then come up with some scheme that does the job without overkill. Some LEDs and comparators, or one of those voltage level ICs (their proper name escapes me at the moment), so they get discrete steps. Maybe making sure the voltage is merely "good" and "too low" is sufficient, so two comparators driving two LEDs is sufficient, or there are neater schemes to have LEDs turn on at a given voltage.

Michael

Newarkinone shows the price as Can$27.52 - wonder what price units that Farnell site uses?

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I posted the link to the Australian Farnell site, so that price is in Aussie dollars

Dave :)

Why not re-engineer the whole system ! Replace the Headlight (bulb) with a Multi-Ultra Bright White LED Array. They don't burn out or drop filaments and require less battery power and will operate on weak batteries, thus eliminate the need to closely monitor the battery Voltage or troubleshoot a no Light Output Condition. Same story for the tail-light ! Multi Red LED Array. All for the price of any DVM. Yukio YANO

I'm with the others on this, re-thinking what you actually need is probably a good idea. I can't see any benefit of having an LCD display for the pack voltage, esp at night when you'll need to backlight it, and it could be distracting. If you simply what to know when the batteries are getting low then a simple single (or multiple) "low batt" LED will do. Use a DC-DC converter to give you a constant brightness on your lamp, and maximize the use of battery capacity. Are you using primary Alkaline cells or rechargables?

Dave :)

You can build one using one pic ADC ch. but you must set vref- 8V and vref+ 20V or you can just divide voltage range to 0-5 V. you can read the measurement with two 7 segment. google "voltmeter with pic" tags this shoud help.

Cheap and tiny, but requiring a bit of cobbling: Get a cheap DMM (often on sale at Harbor Freight for under $5). These have displays about 1/2" high and 2" long. (Hey. you have to be able to read the display! half-inch square would be tought unless you had really tiny digits..) Inside the case is a big rotary range selector switch and a little chip under a black blob. Just figure out which connections are made for the range you want, hot-wire those and eliminate the switch, and install in the smaller case of your choice.

Oh, the DMMs run on 9V, but they don't draw much juice so you can probably drop the 12V with a simple zener circuit.

Best regards,

Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, Signal Generator Science with your sound card!

Definitely inexpensive.

Some (many) DM's can't measure their own battery supply - something the op may run into with the meter he chooses.

The problem can be solved with some diodes to shift the ground reference, but that may make it necessary to change the voltage divider too.

This is for a bicycle lighting system? Needs the back light if it is LCD. I'd go with a color LED bar/dot display and just blink it twice a second. Turn the brightness up during daylight if it is needed, and way down at night.

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Do you mean LM3914

I used 2 of those and a pair of 10 LED bargraphs to make a very nice

20 LED analog voltmeter for my motorcycle, which has charging problems

The LM 3914 can be used anywhere from 3 to 18 volts or so with Very minimal support circuitry. Offhand, I believe the OP could make a 10 segment meter with: an LM3914, the LED bargraph and 2 or 3 resistors. If he needs to calibrate the upper and lower thresholds more precisely, he would need to add two pots to that.

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That's beginning to look like a good option. I really don't want to get into programming a pic chip. This is getting pretty complicated anyway. Maybe I'll just fix it at 13.2 volts and call it a day, and take along my mini RS multimeter.

There are some wonderful HID (metal halide) lights on the market but they cost big bucks.

For tail lighting I'm using a Cateye TL-LD1000 which is red LEDs and has its own AA batteries. This and an amber strobe (12 volts) from All Electronics, this will run off the battery pack (12 alkaline C-cells).

I'm using alkalines because I wouln't always have the ability to charge rechargeables, but you can always buy alkalines.

The headlights, at this time will probably be two 12 volt 10-watt MR16 bulbs (one flood, one spot). Though finding these bulbs is proving difficult.

If you're interested, here's some controllers:

You should look into a 3W Luxeon LED headlight.

I have a luxeon LED flashlight and it is much brigher than any other flashlight that I own.. It runs on 4 AA batteries for approx 4 hours.

- Mike