Tiny led voltmeter - help needed in finding the smallest one


I want to put a volt meter in a light using 2S Li-ion. I remember a long time back, someone on CPF had come up with a tiny one and they used it in a Maglite body. I would love to find the smallest one possible, even if it's just something that would only light if the voltage dropped. I have seen some with led readouts, but they are just too big at 30mm or so.

Anyone have any suggestions on anything very small? (less than 20mm)


Saw some small ones

I’d say you want a 2s lipo alarm. Unfortunately most of the modern ones are built for connecting to the balance connector of a battery pack, you won’t have that (a tap between two two cells). It looks like this one is widely available though:
Doohan 2S Audible Voltage Lipo Alarm

Just remove any buzzers / LEDs you don’t want.

The first place I looked was at Hobbyking but it looks like they only carry the balance tap ones these days.

I use these, very good little voltmeters, won’t power up unless there is 3.2vdc however
I have one tied into one of those cheap portable power units to monitor the voltages going to the battery

https://www.fasttech.com/p/1222900 <-blue
https://www.fasttech.com/p/1222901 <-green
https://www.fasttech.com/p/1222902 <-red

31mm is too big…


For the smallest one possible you could have someone make you one using a dedicated voltage monitor chip. They can light up an indicator led when the voltage drop to the level the chip is preset for. 3.0v Voltage Monitor

Wow, that one’s really sweet Helios-. Where did you come across that?

Yeah they are…that’s pretty cool!

This is the one jayrob over at CPF uses on his mag mod with voltmeter in this thread


This is the voltage monitor used



I don’t recall. i came across it some time ago. Its sort of expensive for what it is IMO.

Thanks for the ideas. Helios- Love those links. AlexGT- Yep, that's the thread, Thanks.

These are what I use on some of my spotlight builds. They are smaller at 23mm X 15mm X 10mm, but might fit in a Maglite. They are cheap and work great.


For just a single 3-5mm panel led could you use an op amp and a few resistors? Might fit on a small board ~ 15mm.

Edit-Like this maybe Matt could help you with the board

seems these days programmable drivers offer a lot of flexibility…it might be possible to program one of these drivers to get the functionality needed
re. Star firmware: https://budgetlightforum.com/t/-/25032

Looked up the data sheet on the 3.0v voltage monitor linked by Helios and found this schematic

Looks pretty simple to use for just one led.

Thats whats so nice about them. Tiny, easy & uses very little current (0.5 uA typ). Also don’t need to be able to program chips. Just connect the voltage monitor chip, indicator led & resistor (aim for <50mA led current).
Haven’t ordered one yet since the attiny can do low voltage detection.


I ordered one weeks ago, I think it is the smallest, with digits

Whoa that is small - size of a sim card. I looked around - cheapest is $5 shipped for these (vs $1.40 for the bigger guy), quite a jump in price for tinyness.

Interesting why the red is always cheaper than green/blue version - easier to build due to Vf probably?

I like the readout style over the lights. It's larger, but if I can fit it in, I will use the readout style. I don't really need a low voltage warning, I just think a readout of voltage would be kind of different.

Cheapest I could find:

Starts as low as 2.5V

Starts at 2.6V