LED Voltmeter

[interestingfellow]

Ok, I'm off to build my first real mod, but do it my way and trying to church it up a bit.

I am a total noob at IEEE, and am trying to further my knowledge through application. NOOB, as in, pre electronics 101, jsyk.

I'm trying to build an LED voltmeter, similar to a stereo UV meter, but each led equals some step in voltage, of my choosing. Not to be vague, but I know the circuit could easily be manipulated to accommodate, 4-10 LEDs, ranging in voltage from 2.x volts to 3.7v (or 6v, 7.4v).I have a vague idea how to do it, with transistors (in a darlington? arrangement?). Anyway, I know this isn't an easy question to answer, and i've googled the hell out of it with only a little luck. If you have a link or know where I can look, that would be great too! OH, I would like to do it analogue, as I'm trying to start at the beginning.

I've been looking at the following two links trying to figure it out, just to give you some idea where my mind is at:Transistor Circuits and http://talkingelectronics.com/proje...nics.com/projects/StereoVUmeter/StereoVU.html

My original thought was to use a small version of this LED voltmeter as the "on" led when vaping, but know that power consumption would be an issue, so A)I would want to use low power LED's etc and/or B)I might just add it as a separate voltmeter with it's own button, so I could use it at will to get a better read on how much battery is left??? Plus, I could make it look cool as hell (let's face it, that's what this is all about).

TIA!

EDIT
Just found this. I'm getting closer

 

[interestingfellow]

And my answer is on the forum. The one place I didn't look at....er, the last place I looked.


For as smart as I am, sometimes I'm just a dumb bass.

Mod, feel free to just delete this "thread"

 

[jrm850]

A voltage ladder?
‪Circuit Analysis - R-2R Ladder Application - Digital-to-Analog Conversion‬‏ - YouTube

 

[interestingfellow]

Thanks for the link!

Q: If the same load were applied to each leg (where "i" was halfed) wouldn't it just be a voltage ladder (since it's not going to an IC)? Is that (the schema in the video) a daisy chained voltage divider?

 

[jrm850]

Thanks for the link!

Q: If the same load were applied to each leg (where "i" was halfed) wouldn't it just be a voltage ladder (since it's not going to an IC)? Is that (the schema in the video) a daisy chained voltage divider?

You are correct. That demo is good in a way because you do want to calculate max current across the LED. Limit the to no more than 20ma and you probably want a lot less than that to limit battery drain. Remember that LEDs are not self limiting so you always need a current limiting resistor if you don't want to let the magic smoke out.

 

[jrm850]

Voltage divider circuits : DIVIDER CIRCUITS AND KIRCHHOFF'S LAWS

This one should help you a lot.

 

[mj64]

So, you wish to build your first mod but actually wish to build your first circuit to go in your first mod as well? Why not baby-step it a little? There are voltage displays available like you describe.... Not criticizing, I tend to do things the hard way sometimes too, just a suggestion.

 

[NicksVap3]

yeah me too, more power to ya though. dont get upset on failure. keep trying. my VV9v is now going to be a TI booster module, with usb charging. back to the drawing board. and good luck to ya

 

[breaktru]

Check out Alan's Dot Graph: Dot Graph Mod

 

[interestingfellow]

Eh, I've built little circuits before as well as replaced a few components here and there.
Mainly, I recently toasted a Phoenix Gold MPS2500, and can't fix it (I'm sending it off):I"m really ...... about that fact, and am now overcompensating

I'm tired.... gonna check those links ya'll threw out, and go to sleep!

Thanks!

EDIT
@JRM
Holy canolies, batman! I googled voltage deviders, but got discouraged because I didn't know what to look for, so I didn't know what to look for. That link was perfect! Now, I just have to find some lower voltage LEDs in my box, and gettit goin!

 

[bstedh]

I think you could do the same thing with 2 or 3 Zener diodes of different values with an LED and resistor on each. The LED's would shut off as the voltage drops below each zener's rating.

 

[jrm850]

Eh, I've built little circuits before as well as replaced a few components here and there.
Mainly, I recently toasted a Phoenix Gold MPS2500, and can't fix it (I'm sending it off):I"m really ...... about that fact, and am now overcompensating

I'm tired.... gonna check those links ya'll threw out, and go to sleep!

If you are doing that kind of stuff then you might want to think about getting started in microcontrollers. You can get started for $20 or so and there are a lot of people willing to help on the web. I personally like the Atmel AVRs but Pics probably have a lot bigger fan base. The biggest expense will be a programmer. You can get a USB "ISP" In system programmer for under $20 on ebay or build your our own for a couple of bucks. You can download a free copy of Bascom AVR from www.MCSelec.com. It's a basic language compiler that I think is a lot easier to get started with than C or Assembly. Chips are pretty cheap. This circuit you want to build would be a great first project. Check out AVRFreaks or the forums at MCSelec to get aquainted if you are interested.

There is also the infamous "Basic Stamp". It is an entry level uC line that is geared towards the beginner and leaves no stone unturned. They sell kits at Radio Shack for around a $100 with everything one needs to get started or they have more options at the website - Parallax Home

Glad the link helped.

 

[interestingfellow]

I knoq me, better than only a few people. The way I learn, I have to understand the old school way of doing things before I move on the the new tech. I have looked at basic and ardueno before, and I have a ton of ideas, but I ain't there yet.

I'm looing at taking a 101 course, or something, so I can do these things.

remember, it ain't hard if you know how to do it.

 

[interestingfellow]

OK, this is just pissing me off!

Looked into voltage dividers, brushed up on ohm's law, got a breadboard and some other stuff, and sat down to do this; four times. And I can't get this thing to work.
I'm going off of an accurate external led voltmeter.

I set up the bread board with several LED's (in parallel) of different ratings, 50MΩ pot, 5v 700mah power supply and a switch. hook it all up, turn it on, and start creeping up the voltage till led's each led cuts on, and write it down. go back a voltage for a particular led, pop one of it's legs, insert my dmm/ammeter, and write it down.
run through some calcs (still not sure about that), redo the bread board with a voltage divider using 4 1kΩ 1/4watt resistors and 5 uv leds (cut on of 2.7v, current draw of 31uA each), and it just don't work right. @4v 1 led is full bright,and the next is just barely on, and the rest are off.


As badly as I just want the answer, I also want to learn how to do it and don't know enough to know what to ask. please help?

 

[mj64]

I'm just a little interested in your masochistic quest and am following along. I probably understand this less than you do, but I'm REALLY good at searching for things.

Maybe this will help.
Six-LED Bar Power Indicator - RED - Page102