Mini Digital Volt Meter Ideas  (Update available)  Superseded

I’ve got this homemade power supply that I’ve been wanting to put a meter on for a long time and in the past I had choices like analog meters and the they look like this minus the control down here. As you can see it’s just too big, they take up a lot of space and they are not all that accurate. and then there’s this bar type but the bar type well frankly it’ll also take a lot of space and to not all that accurate. So the other day these have been out for a while, but the other I found one of these Thought I would put it on here. Let me tell you a bit about them They are rather interesting, little self-contained digital volt meters This is a 3-wire system and what that means is that you power the meter with voltage between the red and the
black It can vary a lot. This particular one is between 3 and 30 volts it operates And that is these 2. And the sensing is a between the black wire over here
and the white wire and it will sense the voltage and that’s what comes out on the readout, what’s between the black and white wires and ths one they told me will sense between between 0 and 50 volts. Right now I’m
running it on a battery pack but by simply touching the white wire on the red wire I can measure the voltage of the battery pack which is showing 2.9 volts. I can power it with 1 power and
measure something completely different. I can show you and example of that with a quick and dirty volt meter. Also this is all self-contained very tiny you can see. I can mount it on the outside It’s got little ears. I’ve got lots of space for it right here. It not going to be an issue With the 2 wire system it takes about 3 volts before the display cames on So it obviously will not measure anything less than 3 volts but with this one I can measure, well right now I’m getting zero volts The power is on so clearly I can
measure measure a lower voltage than it takes to operate the display LEDs That is the benefit of the 3 wire system. I can read much much smaller voltages down to 0.1 volts in this case As an example of what you can do with these digital volt meter displays I taped one (you could mount it permanently) on to a battery holder, there are a couple of battieries in there turned it on and then just connect the common (black) and the sensing on to my target and 1.50 volts and that’s correct for this battery So now I have mounted this digital volt meter on to my power supply and it works very nicely. Just screwed it on the front, used some foam tape on the back to insulate it from the box and you can see I can pretty accurately
control the voltage much more convenient so yeah I’m really sold on these. Much better than the analog option or the the digital bar level option That’s it. Hope you found it interesting

15 thoughts on “Mini Digital Volt Meter Ideas (Update available) Superseded

  1. I have one that measures 0-100V, I haven't been able to find the current rating on it though, what can it intentionally handle?

  2. I don't know why but mine is not at all accurate. It's off by 0.15 volt or something like that. Do you have any tips on making it measure better?

  3. You can get 3D or injection molded bezels for these so you can make a rough cut with a dremel, then put the voltmeter in the bezel and bezel in the hold you cut and it looks much nicer! Just google .36" led bezel for the one you have, .28" for the smaller ones, and .5" and greater usually come with a bezel. Also, the different colors tend to have different threshold voltages. In my experience the red 2 wire ones come on with the lowest voltage.

  4. So if it has only two wires you just hook the meter wires to the voltage and it will read voltage? Or is it better to have a three wire meter?

  5. I killed this volt meter on a DIY battery adapter I made. I wanted to test the real time voltage of an 18V L-ion battery while in use on a jigsaw so that I could remove the battery before it discharged too far (the tool did not have any battery protection circuitry). It worked well showing 20.3 volts while the battery was connected but as soon as I used the tool the little volt meter died. I'm assuming that the current was too high under load or even just while running the motor. Can someone point me into the right direction to wire this properly or a better strategy to see battery volts of a drill battery? Thanks!

  6. So a bit more…these basic versions usually come with a unmarked microcontroller, but if you check the Vcc and ground pin locations you will clearly see the PIC configuration. Most of these are PIC16F683's these days. There used to be some that were sold with an STM8S103 MCU but that chip is usually only used on the larger dual volt/current meters these days. The manufacturer of these changes components and will periodically change some parts of the PCB design to accommodate cheaper parts availability.
    There are 2 common sizes for these cheap meters 0.28" and 0.36." Personally I find the 0.28" version is far more versatile. These meters are only as accurate as the resistor voltage divider and internal voltage reference of the PIC microcontroller and 10 bit ADC. There are 4 digit meters that use an external 12 bit ADC and, IIRC some of the 5 digit models come with a 16 bit external ADC. It's been awhile since I looked into the 5 digit version but I believe they are using a second sourced Maximum Integrated ADC. IIRC it's the cheapest high resolution instrumentation type ADC I could find. The 5 digit meters cost as low as just under $4 (AliEx) and the cheapest comparable chip (including searching for the one used on the meter) was $6+.
    Anyways… these are handy little devices.

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