Electronics > Beginners
Trying to make an LED voltage meter (Dot mode)
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evglabs:
I'm trying to make a little project that would be an LED voltage meter, but I have a few requirements that I'm not sure how to implement:

I need all components to be surface mount, through hole is a deal-breaker.
Powered by 2 CR2016/CR2032's in series.
Between 10-20 LEDs BUT in dot mode, so if the 5th LED is on, 1-4 would not be.
And small, the circuit needs to fit on a credit card sized PCB.

I'm aware of the LM3914 but the only surface mount I can find is about $3 and that blows the budget.

I know I could do this with a microcontroller but the project is more for learning, so I figure there's got to be a way to do this without one.

I'm thinking the voltage signal would be coming from an opamp (so I can adjust the gain and offset) then to whatever circuit to drive the corresponding LED. If I adjust the gain and offset so the range would be 4.0V to 5.0V each LED would correspond to a 0.1V step.

Also the LED's do not need to be bright (in fact it would be better if they were more on the dim side for power consumption).

Thanks, I hope I explained myself (I'm still very much a beginner to electronics).

I should say, I don't really need the circuit designed, I just don't know WHAT to look for to design it.
MarkF:
Here are two options:

(However, I think you will end up spending more than you would with a LM3914, LM3915 or LM3916 in the long run.)

Bargraph with three LM339

Bargraph with transistors
evglabs:
Thanks, but I really need it in dot mode (so only one led is lit at a time). That's the main part I'm struggling with. I can't figure out how to turn off previous LEDs.
MarkF:
Oh, I missed that.
Just to confirm, the LM39xx series already does this?  You just want to cut cost?

You could setup voltage windows with the LM339.  But, six LM339's and logic chips would break the bank.
evglabs:
Well, cost and size. I want it to fit in my pocket without having the through-hole pins tearing it up.

Yeah, the LM391X can do either bar or dot modes.

But, VOLTAGE WINDOW! Thanks, I was missing that term! I may just have to go with a microcontroller for cost, but I knew there had to be a way to do it without one!
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