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Small LED voltmeter

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debe

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Purchased a few of these of Ebay for $1.36 + .81c frt. They are 3-30V DC digital volt meters, they come in red blue & green displays. Went for blue as they were advertised to draw the least current, this one draws 13ma reading an old 9v battery. On the back there is a pot for adjusting the accuracy of the reading if you aren't happy with it. In real life the colour of the display is even, just it was very difficult to get a picture due the multiplexing of the display, camera didn't like it.
DVM.1.13Ma.JPG
DVM.2. 13Ma.JPG
 
What is your question?

Or are you simply showing us the device? (Nice little rig for the price! Can you provide the site address?)
 
Here's one source. I'm going crazy at this site! Buying since August. Happy customer.
Edit: Seems I bought one :) Blue. As described. Works well at 4vdc.
Do not measure the supply voltage running the module!
Do not try to measure - voltage (with respect to the test leads) you will just see 0.00 volts.

**broken link removed**

Description :

MINI DC 0-32V 3-Digital LED Display Voltmeter

Features:

Low start-up voltage, the red minimum 2.5V, green minimum 2.7V, blue minimum 3.0V.
Supply voltage is lower than 3.5V, the only decrease in brightness, but does not affect measurement accuracy.
Has reverse polarity protection, reverse does not burn.

Specifications :

Measuring range : DC 0V--32V
Input range : DC 2.5V-32V(Max Input : DC 32V. The device can be damaged if input is over 32V)
Red DC2.50-32.0V, Green DC2.70-32.0V, Blue DC3.00-30.0V
Display : Three 0.36 "digital tube
Measurement accuracy : 0.1%
Refresh rate : about 300mS / times
Input impedance : About 100K
Operating Current : Red <23mA, Green <18mA, Blue <13mA
Dimensions : 33mm*15mm*10mm
pitch of holes : 28mm
aperture size : 2.8mm
Operation Temp : -10℃-+65℃
Display Color : Red, Blue, Green
Lead Length : 15cm
Wiring :
Red : power supply +
Black : power supply -, measure -
white : measure +

Package included :

1 x 3-Digital LED Display Voltmeter
 
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They are great little voltmeters, I bought 3 of them put one in the car and the other two on my battery chargers. They are very accurate and cost only a few dollars with free postage worldwide.
 
The low cost probably also describes the quality, accuracy and reliability.
 
Caveat Emptor.

Having said that, at that price range, one can purchase several and just discard the faulty ones.
 
Caveat Emptor.
Having said that, at that price range, one can purchase several and just discard the faulty ones.
I think that cheap junk is a problem waiting to happen, and again and again and again and again ......

I got a new job then bought a high quality Fluke multimeter for my projects at home. Then my new boss bought a cheap multimeter at Radio Shack for work. It lasted a few days but my Fluke still works perfectly 20 years later.
 
For that price I don't rely care, bought 6 of them & they were all within a range of .02V of each other. In most aplications that's good enough. Price these days seem to reflect volume production as well.
 
I researched the Holtek microcontroller in the photo.

It has 12 bit A/D converters, which is an overkill for 3 digits. However its reference is its own Vdd supply.
Therefore its accuracy is related the voltage regulator's accuracy (which is, I suspect, the reason for the trimpot).

Long term drift is another thing, but if one has a reliable meter (Fluke, for instance) to calibrate them against say, every 6 months, one should be ok.
 
I got a new job then bought a high quality Fluke multimeter for my projects at home. Then my new boss bought a cheap multimeter at Radio Shack for work. It lasted a few days but my Fluke still works perfectly 20 years later.
Mine too but almost 25 years
 
I researched the Holtek microcontroller in the photo.

It has 12 bit A/D converters, which is an overkill for 3 digits. However its reference is its own Vdd supply.
Therefore its accuracy is related the voltage regulator's accuracy (which is, I suspect, the reason for the trimpot).

Long term drift is another thing, but if one has a reliable meter (Fluke, for instance) to calibrate them against say, every 6 months, one should be ok.
I would not want to recalibrate them all the time.
Calibrating with that kind of pot is a joke.
 
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