Modifications to LED Bar Graph Volt Meter for 12volt batteries(and Battery banks)

Hi I found this LED bar graph voltmeter at

I want to understand how to build this voltmeter.But please read the solorb website page before posting, for more info.

1. What is an offset resistor???
2. What is a 'span'(see pic notes)
2. For 12v operation,short J2 and J5,but what to do to all the other unconnectd 'J 'wires, just join the wires or what?
3.To use without the Blue LEDs, just remove the two LEDs or any other connection/shorting is required????
4.What is switch S1 used for ???, I do NOT want to manually push switches while the meter is in operation.
5.How to stop the blink-LED mode, I want the constant display mode always.
6.There is also two arrows shorting two pins on the IC with words 'Adjust for 12v'?????????
7.How to calibrate the circuit accurately???

PS:- If you want to know more about a larger part of this project,visit


Picture of Modifications to LED Bar Graph Volt Meter for 12volt batteries(and Battery banks)
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I have to say thats one of the best documented projects I have seen quoted on here. I don't really see why you have any difficulty. Read the circuit theory. I think its a pretty neat little circuit. You'd improve the efficiency even more wih high efficiency Leds not ordinary ones. 1.) Offsets the bottom of the internal resistor chain so it starts at 10.5 V and not 0 2.) Makes sure the top LED lights at the right voltage (15.0) 3.) Do exactly what is says on the packet. Short J2 and J5. Clearly that means don't short the rest. 6.) Yes, so there are. 7.) Wonder what "adjust to 12V" has to do with calibration ?????? Could be more accurately drawn. Measure the voltage between pins 4 and pins 7 to, well, 12V 4.) Just remove the Leds DON'T short ANY connections. 5.) Like it says, it locks on the circuit
mhkabir (author)  steveastrouk8 years ago
Also, leave the J1,J3,J4disconnected,just like that,three disconneted wires sitting there?? It also shows, Pin 9 on the Ic is connected with Pin 11 , should I leave them as is,when removing the blue LEDs? Sorry,about my Qs, i'mpretty much a no brainer on advanced electronincs:(
If you look at it, and you're using it on only 12V, the regulator u3, r7,c3 and c4 are not needed, so there ARE no links J1, J3. Omit R6 as well. Leave 9 and 11 linked. Steve
mhkabir (author)  steveastrouk8 years ago
Thanks for the quick reply.But where is R6? PLEASE i beg you to show me what is a offset resistor!!
Have you read the 3914 data sheet ? Internally, the 3914 has a chain of resistors followed by a comparator. Each comparator measures a node on the chain of resistors. OK ? Now, if you fasten one end of the chain at 0V, and the other at 10V, you will get one LED switcing on at 1V, the next at 2V etc etc...which is not what you want, is it ? No, you need to OFFSET the bottom of the chain ! So that first LED in the 3914 sees 10.5 on it, the next 11.5 etc. This is trimmed with the span control.
Also, it appears that the blink mode is enabled by cycling power to the 3914, by turning Q1 on and bringing that rail to ground. If you removed Q1, U1, and the support circuitry for those two parts (lower left part of the chip), and jumpered Pin 2 of U2 to ground, it would always be on.
mhkabir (author)  steveastrouk8 years ago
Understood.But the variable resistor 3 has pins,right,but which pins to connect on the circuit? VR 2 has just '200' written on it?Is is 200K or 200 Ohm?Also why does only VR 3 have an arrow on it and why not VR 1 and 2?
VR3 is configured as a variable resistor, Vr2 and 1 are configured as potentiometers, so the RATIO of voltage across the terminals varies. Fasten the centre pin of Vr3 to one end - making it a two terminal device. Steve
mhkabir (author)  steveastrouk8 years ago
THANKS!!!!!!! Now Finally i have understood the mechanics of this circuit!!
mhkabir (author)  steveastrouk8 years ago
I did not understand about the offset resistor,how to they work ?*No Help In Googling*