# DC votmeter circuit design

Discussion in 'Electronics Homework Help' started by fromdawest, Nov 17, 2012.

1. ### fromdawest

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Nov 17, 2012
I want to design a circuit with a 7 segment display, which can show the voltage of a source connected to it . I saw many diagrams using ICL7107 for this but non of them exaplains the programming part . Could you please teach me how to make it step by step please ?

And the other thing is, if there is any posibility of using a LCD display to show the values, let me know the way i should follow .

many thanks,
from da west .

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,496
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Jan 21, 2010
There are as many ways as there are people who might offer you advice.

Basically, it will boil down to, do you want to use a migrocontroller or not.

If you do, then it is a simple case of doing some sort of A-D conversion (most probably using an ADC in the uC) and then writing code to convert this value into a pattern of outputs corresponding to the output device you've chosen.

The output device could be a meter (yes analogue!), a string of LEDs (although you wouldn't need a uC for that either), a single 7 segment display, several 7 segment digits, and LCD display, or almost anything else. The world is your oyster.

However the problem sounds like a school project, so perhaps you can tell us more about the constraints you're under?

If you're planning on using a uC, then the first thing you need to do is to learn how to program one (and there are millions to choose from, so even earlier you'll need to pick a family of devices).

Maybe a PICaxe would be suitable.

3. ### fromdawest

7
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Nov 17, 2012
Thanks and need more help on this

Hi Steve thanks for the reply ,

Yes its a highschool project which I should complete within next two weeks .

What I basically want is, to make a circuit which can sense the voltage and the current ( going through it that instance of time ) of a particular power cable ( like a twisted cable with live and neutral ) .

As an example, let say a INDUSTRIAL SOCKET with wire which is designed to send high currents and to work under high voltages ( 32A / 500V like range ) . So what I want is a device to measure the voltage and current of such a power cable . So you may think I can probably use a FLUKE multimeter, yes i can, but we are asked to make our own circuit to do this . Simply think we are installing this circuit to that industrial socket, so the socket has an indicator of voltage and current, and that should be digital .

Constraints are,

1. The circuit should have LCD ( 16x2 like lcd ) to show the voltage and current of the cable

2. The circuit should be based on a PIC micro controller . And for the PIC and the circuitary, the power must be obtained from the same power line we are measuring the voltage and current . ( as the circuit takes a very little current, i think that will not put a big impact of the load connected at the end of the power line, if I'm wrong please tell me )

3. The circuit should be able to measure votages from 0V to 600V ( atleast up to 500V ) AC voltage . And the current from 0A to 32A ( better if its possible to measure up to 60A or more ) .

4. When the cable is not connected to any source, the LCD display shows nothing and the circuit is in off state . But once when the cable is connected to a source and a load, that circuit gets power from it and indicates the voltage and current .

I have downloaded a PROTEUS files of a DIGITAL VOLTMETER from internet . But that can measure up to 30V maximum . So if its possible to increase this range up to 500V, please let me know the modifications .

http://www.electrosome.com/voltmeter-ammeter-pic/

From da west .

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4. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,496
2,837
Jan 21, 2010
You have an awful lot to do in 2 weeks. I suspect you had longer than this to work on it?

The circuit you refer to is for DC, and it sounds like you're talking AC which is a different kettle of fish.

Having this device line powered and measuring mains voltages on a PIC seems foolishly dangerous.

There are some hall effect current measuring devices, or you can use a current transformer to safely (relatively) measure mains current.

5. ### fromdawest

7
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Nov 17, 2012
Any help

Steve,

But could you please tell me a possible way to make this ? any tutorials ? could you please accept my request on skype then I can have easy help from u i guess .

Thanks,
Dileesha .

6. ### fromdawest

7
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Nov 17, 2012
I looked for sensors, and there are some sensors that can measure the current in the wire . but m not sure whether such sensing circuitary can be used with the pic . is it possible ?

7. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,496
2,837
Jan 21, 2010
My recommendation is to go back to your original idea for a single digit digital voltmeter.

It's safe and will provide almost all of the same learning opportunities without the danger and complexity.

Sorry, don't have time for skype right now.

8. ### fromdawest

7
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Nov 17, 2012
ok thanks steve ...