PIC 16f877 A/D conversion Allegro ACS712

[DavyJones]

It does not use an ACS712 in that circuit.

I'm showing the LTC1966 RMS convertor, which is needed whether the signal comes from a current transformer, a hall-effect sensor, or just a BIG honken resistor that would heat your toaster oven.

It's the RMS conversion that matters.
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I am sorry I am not trying to tick you off or anything but I have to question this one last time. What is pumping the same signal through the LTC1966 going to give me that I can't figure out myself? I guess that is the part I am having trouble comprehending. The ACS712 data sheet says it's good for sensing current for motor control, load detection, etc... No matter what the ACS712 is going to output a voltage that is in direct proportion to the current it senses. Granted it's going to follow the wave form of the AC current it's still going to be proportinate to the peak current arghhhhh I need to go do something else for a while and stop thinking about this.
I'm not giving up on this I know I will get it.

[Darrel Taylor]

I must sound terrible in my replies.
Everyone thinks I'm getting ticked off.

Tuff!

But when I see someone going down the same bad path I took, I'll just keep tugging on your belt trying to pull you back, saying ... Duuude, there's a cliff up there. Don't go that way.

Let's see here ...

The ACS712 data sheet says it's good for sensing current for motor control, load detection, etc...

It IS!
As long as you know how to compensate for the type of load you are measuring.

No matter what the ACS712 is going to output a voltage that is in direct proportion to the current it senses. Granted it's going to follow the wave form of the AC current it's still going to be proportinate to the peak current arghhhhh

Not at all.
With RMS the peak doesn't matter anymore. The entire waveform is averaged over time, to represent the amount of current that flowed during a specified time period.

Small motors will generate fairly high peaks, but since there's not much load it can overcome each magnetic pole fairly quickly. So a short duration current flow over the course of 1 AC cycle will average out to maybe one fifth of what you would read from a "Peak value".

I'm not giving up on this I know I will get it.

I hope not. You've already ordered the parts.

When you get down to doing the math. Come back and describe the parameters. I got that part down.
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[DavyJones]

No your posts don't sound horrible I'm just anticipating or hearing you in my head "What don't you get you idiot!" I'm just struggling with this my knowledge about electronics is below novice. I'm having trouble though locating the op am you mentioned TLV324 it looks like that comes up as a switch of some sort not an op amp.
Thanks
David

[Darrel Taylor]

Oops, that would be a TLV274.

I knew I should have checked that.

TLV274 is a rail-rail version of the LM324.
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[DavyJones]

Oops, that would be a TLV274.

I knew I should have checked that.

TLV274 is a rail-rail version of the LM324.
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Wouldn't you know it Digikey doesn't stock any.... argh

[DavyJones]

Wouldn't you know it Digikey doesn't stock any.... argh

How about the TLV271 I only need one for my test. I think I will ultimatley need the TLV272 because I am controlling and trying to read the current from 2 pumps.

[Darrel Taylor]

Yeah, only available in the TSSOP package.

I agree, those are good alternates.
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[DavyJones]

Darrel, I think I might understand now I know that we are off subject from a general pic discussion but I'm going to keep going in this thread it does pertain to working with a pic ultimately so....

I think I am picturing this correctly now. If I take a thousand readings from the PIC and just keep track of the max at some point I will get a peak let's say it's 12 amps. But like you are pointing out that is truly a peak if we were able to get a sample at the top of each waverform over time it would average out to 9 amps which is the true power. The fact that when I sample the A/D I have know idea were in the wave form I am at, at any given point in time, makes it impossible to do just sampling the ACS712 by itself. If I could get a reading form the ACS712 at the top/bottom of each wave then it could be done but then that is what the RMS to DC is going to do for me give me a nice straight DC line.

Did I get it?