# AC Voltmeter

Discussion in 'General Electronics Chat' started by olvine, May 20, 2014.

1. ### olvine Thread Starter Member

Mar 10, 2014
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0
Hey

I want to make AC voltmeter using microcontroller. To feed this voltage to microcontroller first I need to scale this AC voltage to controller's input voltage range. For that what should be methods to do this. Or what are the options ?
voltage range: 0-500Vpp.
Method in consideration: Simple voltage divider.
what else ?

2. ### olvine Thread Starter Member

Mar 10, 2014
99
0
PIC16F887 or PIC16F1827 are available

3. ### inwo Well-Known Member

Nov 7, 2013
2,435
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What value and wave form do you want to measure?

4. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
515
The division ratio will depend upon frequency and may need compensation.
Have a look in the service manual for an oscilloscope and see how they do it.

5. ### olvine Thread Starter Member

Mar 10, 2014
99
0
range is 0-1000Vpp and sine wave

6. ### olvine Thread Starter Member

Mar 10, 2014
99
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Need to make a digital AC voltmeter. simple resistive network can do the task but I want to know other methods for scaling of AC signal

7. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
515
You may have misunderstood my comment, which is why you have not told us what frequency range you are working in.

A resistive divider may be appropriate, the actual topology will depend upon source and load (voltmeter) impedences.

But if your voltmeter is going beyond mains frequencies, even only audio, then you will need some compensation.

Last edited: May 20, 2014
8. ### olvine Thread Starter Member

Mar 10, 2014
99
0
This simple circuit works fine with 10kHz sine 1000Vpp.

But the frequency is 60Hz for which I would be designing a meter.

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9. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
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So what is the capacitor doing in your divider?

Is this a real exercise or just a theoretical one in a simulator?

10. ### olvine Thread Starter Member

Mar 10, 2014
99
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Kinda compensation.

and without capacitor I am getting the same results

11. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
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But wasn't that in a simulator?

12. ### olvine Thread Starter Member

Mar 10, 2014
99
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Yes it is in simulator.
I suppose proteus not a good simulator then

13. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
515
It is not that, it is that components, particularly resistors, are 'ideal' and the circuit cannot add a random amount of stray capacitance or lead capacitance.

Do you understand why (and therefore when) compensation is needed?

As already said, you will not need compensation at 60Hz.

14. ### olvine Thread Starter Member

Mar 10, 2014
99
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Yes understood. Thank you

Nov 9, 2007
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16. ### olvine Thread Starter Member

Mar 10, 2014
99
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transformer increase cost and that's why it can't be considered.

I have also considered capacitor voltage divider but may be we need to consider the frequency too.
Their are other methods like using thermocouple and hall effect sensor but I don't think they are good enough to implement.

17. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
515
How about a valve voltage follower with fractional gain?

18. ### olvine Thread Starter Member

Mar 10, 2014
99
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This is something new...lemme check this

19. ### studiot AAC Fanatic!

Nov 9, 2007
5,005
515
This was a common trick in the old days using a cathode follower probe.

You could do it a transistor, but 1000volt transistors are not so cheap.

20. ### olvine Thread Starter Member

Mar 10, 2014
99
0
Are you considering that I need to make a digital AC voltmeter and for that some analog external circuit is required to attenuate the AC signal of higher voltage to microcontroller's allowable voltage ?