Log analog data from Kill-a-watt?

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Luke7
 
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Log analog data from Kill-a-watt?

Post by Luke7 »

Hi, looking for help.

Trying to log analog voltage & current values directly from the LM2902N chip without using an x-bee. Is this possible?

I've tied into pins 1, 4, 11, 14 and tried process of elimination with a multimeter and cannot find any link between the values measured by the kill-a-watt & the multimeter.

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Franklin97355
 
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Re: Log analog data from Kill-a-watt?

Post by Franklin97355 »

Luke, since you are not trying to use the xbee this post would be better suited for the general projects forum. Are you measuring AC voltages?

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adafruit_support_bill
 
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Re: Log analog data from Kill-a-watt?

Post by adafruit_support_bill »

[moved to General Project Help]

Luke7
 
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Re: Log analog data from Kill-a-watt?

Post by Luke7 »

franklin97355 wrote:Luke, since you are not trying to use the xbee this post would be better suited for the general projects forum. Are you measuring AC voltages?
I was/am trying to measure VDC signals directly off the LM2902N chip. Looking to get one signal that represents AC voltage & another that represents current.

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Franklin97355
 
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Re: Log analog data from Kill-a-watt?

Post by Franklin97355 »

I was/am trying to measure VDC signals directly off the LM2902N chip.
the outputs of an opamp with ac inputs will be an ac output.

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zener
 
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Re: Log analog data from Kill-a-watt?

Post by zener »

Right. So if you set your meter to read AC volts then you might find something useful, assuming the meter doesn't interfere with the circuit.

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greyf350
 
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Re: Log analog data from Kill-a-watt?

Post by greyf350 »

There are 3 points of interest on the KAW. There's a voltage divider stage that is a divide-by 100 or 122 depending on how recent your KAW is, and there are 2 current measurement stages, one with a gain of 40 and the second with a gain of 400. All 3 opamp outputs have a dc-offset of approx 2.3V. The 2 current stages are used for a coarse and fine current measurement by measuring the voltage drop across a 21 milliohm shunt. Only the voltage and coarse current opamp outputs are used by the TAW example

Since there's a 4.7K/10K divider in front of the XBee ADC input used for level shifting on the TAW, you'll need to factor that in as well.

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