7968 Views 5 Replies Latest reply: Jun 2, 2014 11:07 AM by baycollie
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# VA Meter thru MCU

Hi guys. I'm trying to make a VA Meter by getting real time data from a rectifier using a microcontroller. The circuit uses a voltage divider to get voltage (A0 Pin) and the drop accross the shunt  resistor for current (A1 Pin). When I apply a rectifier though only the A1 Pin gives a signal, I don't get a reading from A0.

Any idea on why this is?

I attached a snap shot of the circuit, it's pretty basic.

Edit: i attached the image

Attachments:
• 13 posts since
May 21, 2014
Currently Being Moderated
May 29, 2014 5:26 PM (in response to JohnDavis)
VA Meter thru MCU

Hey John,

I don't see your attachment circuit. . .

would you mind re-submitting it?

Thanks

• 9 posts since
May 29, 2014
Currently Being Moderated
May 31, 2014 1:37 PM (in response to JohnDavis)
VA Meter thru MCU

The description of what you are doing is vague. It appears that when you say "1A read 2A" it means that 2 amperes are measured flowing through the .47 Ohm (R3) resistor. In other words, using OHm's law .47 Ohms times 2 Amps equals .94 volts across R3. Is this what you are measuring ???

Again using Ohm's law, A0 would then read ' .94 volts times 100k divided by 105k equals .895 volts ' ???

It would help if you could tell what you are measuring ( volts, Amps, Ohms) and how you are measuring it (with a meter ??).

• 13 posts since
May 21, 2014
Currently Being Moderated
Jun 2, 2014 10:28 AM (in response to JohnDavis)
VA Meter thru MCU

John,

Sorry it took me a while to reply.  What type of microcontroller are you using?  Can we see a snippet of the code?  Your system looks very simple, which makes me assume that your issue might actually be a coding problem. . .

Instead of doing RTM on the system, you might just do an intterupt that periodically samples and records the voltage and curent on pin A0 and A1. . .

If you can tell me the controller/code or both, I can only reccommend checking your code to make sure your not lossing the voltage data.

• 9 posts since
May 29, 2014
Currently Being Moderated
Jun 2, 2014 11:07 AM (in response to JohnDavis)
VA Meter thru MCU

Not to leave the uanswered questions about what was being measured hanging. The point is: That there is nothing wrong. If current was being measured at A0, then 0 is the measurement that a meter would show, if it was on the same setting used to measure  the 2 amps at the .47 Ohm shunt resistor,  since only .00000895 amps would be flowing through the 100k resistor.

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