AC Voltmeter

Thread Starter

olvine

Joined Mar 10, 2014
99
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 ?
 

studiot

Joined Nov 9, 2007
4,998
Method in consideration: Simple voltage divider.
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.
 

Thread Starter

olvine

Joined Mar 10, 2014
99
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.
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
 

studiot

Joined Nov 9, 2007
4,998
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:

studiot

Joined Nov 9, 2007
4,998
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.
 

Thread Starter

olvine

Joined Mar 10, 2014
99
Yes understood. Thank you

Can you please help me out with some other method to attenuate the AC signal to controller's ADC input level ?
 

Thread Starter

olvine

Joined Mar 10, 2014
99
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.
 

studiot

Joined Nov 9, 2007
4,998
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.
 

Thread Starter

olvine

Joined Mar 10, 2014
99
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 ?
 
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