# 0-6v LED Voltage Indicator

Discussion in 'The Projects Forum' started by slplsnts, Jun 25, 2008.

1. ### slplsnts Thread Starter New Member

Jun 25, 2008
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I have a 0-6v hand crank generator that I would like to wire to an LED voltage indicator. The ideal solution would not need a constant source voltage. I have found several schematics with LED's in parallel with resistors but unfortunately I do not have the know how to design this circuit.

An off the shelf purchased solution would be best. My kids and I don't need the experience of building this. I will build it if need be. I have purchased a small R/C battery (6v) testor but it does not give a real time indication. It does have several LED's from red, green, yellow which is effect I would like.

Thank you,

Ken

Apr 3, 2007
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3. ### Wendy Moderator

Mar 24, 2008
20,764
2,534
Are you wanting to make a resistor/LED only bargraph? I've done it, and designed it, for robotic batteries indicators. They work, but are very sloppy, one LED starts lighting before the one under it is fully lit.

I can talk you through it if this is what you want to do it. First thing is you have to have the individual voltage drop of each LED, hopefully they will be more or less the same value, but if not they can still be used. You put a resistor divider next to the string of LEDs, one resistor next to each LED. Figure out the voltage on the bottom resistor that matches the LED, the figure out what the second resistor has to drop, etc.

I'll through out a design when I have time. I even wrote a simple BASIC program to help calculate the values of the resistors, the bottom resistor has to be the biggest resistance, the second slightly less, etc.

There are better ways though, the resolution on this bargraph is pretty bad, about the voltage for each LED, more or less. The key question is whether you want the display powered by the same battery?

4. ### slplsnts Thread Starter New Member

Jun 25, 2008
2
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The idea is to show kids how much "work" it takes to light the LED's. The fact that one lights before the other is fully illuminated is fine.

Thank you for the help,

Ken

5. ### SgtWookie Expert

Jul 17, 2007
22,182
1,728
Attached is a schematic of a 0v to 5v 10-LED Bar Graph voltmeter made using a National Semiconducor LM3914 IC and a 10-segment LED bar display, with a couple of resistors and a capacitor.

To change it to read from 0v to 6v, replace R2 with a 4.6k resistor. That's it.

You can power the circuit with a 9v transistor battery.

It does not get a whole lot more simple than this to build a 10-segment voltmeter display at home.

The schematic came from page 2 of National's datasheet.
http://www.national.com/mpf/LM/LM3914.html
http://www.national.com/ds.cgi/LM/LM3914.pdf
Jameco supposedly carries the LM3914N-1/NOPB for around \$1.55, but their server is down at the moment.
Jameco does not have a minimum order like many suppliers do.

• ###### 0v to 5v Bar Graph Meter.PNG
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Last edited: Jun 26, 2008
6. ### bobank Member

Nov 19, 2005
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Thank you for that part of explanation, but there are few things to confuses me. Off course i am new in electronics, although my great assigments I was able to do it without problems, like to screw lightbulb without any failure. Other than that , I am doing mostly drivers and learing about drivers for, LEd, Luxeons, Rebels. Just short introduction, so you do not think you are actually talking to my great countryman Nikola Tesla ( I am Serb, too. He was Serb also, although he grew up in the part that today belongs to Croatia- what I do not have problem in whatever Nation group you put him as when I left Yugoslavia it was still great county without war).
So, to come to main subject, you can see that there are 2 red circles. Question is, where do I bring that supply to circuit- from one source or from 2 sources? ( it looks one source is 0-5V, the other 6.8 to 18V). As I am closer to seeing undertaker from bottom view than graduating from Electronics school, any help will be greatly appreciated. Also, as I couldn't get bargraph display today, I will order tomorrow from goldmine, but could I just use 10 leds, instead one bargraph????
Boban Klasnikov

7. ### SgtWookie Expert

Jul 17, 2007
22,182
1,728
The 0 to 5v source will be where you connect your generator to measure it's output voltage.

The 6.8 to 18v source is a 9v transistor battery - that powers the LM3914N circuit and the LEDs.

The generator doesn't power the circuit; it's output is merely measured by the circuit.

Certainly, you can use individual LEDs. It's quite a bit more compact if you use a bargraph LED though. Radio Shack used to carry them

Electronic Goldmine has a \$10 minimum order. You might try Digikey instead. They'll ship very small orders via 1st class mail, which will save you money.

8. ### bobank Member

Nov 19, 2005
21
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Thanks, I already ordered bargraph,2nd day shipping from goldmine.
I really like learning electronics but my low free time ( I am emergency automotive locksmith), and language barrier ( although I am still OK with English, till it comes to specific thematics) .On a few last schematics I have seen markings JP1, JP2, what looks to me more like some connectors, unless ir is some specific electronic elements i am not aware of it. It would help to know what is it before I make mistake on that field
CAPITAL LETTERS ARE FOR EASY NOTICE FOR SPECIAL ANOUNCMENT:
All other members, in a case that you read this part and that YOU like working with LED or Luxeon light, there is Smooth-on.com company in Easton, PA. They make casting material, so if you have an idea to make some producet with LEDs and need clear =glass look material in specific shape - not to look like plastic box from ULINE, you can check thier web site - do not be confused, they have so many products that you do not know what to buy. Any advice, I will be happy to write back as I have some experiance with thier products.
My plan is to make from 1 pc of luxeon rebel or K2 flasher to replace flare on the road when your car break down. Soon I am done with it ( and will take a month) I will post it so you can make some for your own use.
Thanks to everybody for help
Boban Klasnikov