tweet-a-watt--> data logger

[pherzmar]

I want to combine the Tweet-a-Watt kit with the Data Logger kit. Instead of tweeting the output of the Kill-a-Watt I want to record it with the Data Logger.

My problem is I don't get a voltage out of the Kill-a-Watt that varies with the current of the device plugged into it. I want the Data Logger to read that voltage.

The Tweet-a-Watt instructions say:
Connect Kill-a-watt LM2902N chip pin 1 (current sensor ) to the XBee AD4
Connect Kill-a-watt LM2902N chip pin 14 (voltage sensor) to the XBee AD0

I want to connect the pins 1 and 14 to the data logger analog read inputs.

The voltage on pin1 (compared to the ground on pin 11) should vary when I plug different appliances into the Kill-a-Watt. It doesn't. It should reflect the different current draw. All I get is 2.344V on my volt meter no matter what I plug in, and no matter if the appliance is turned on or off.

The voltage on pin 14 should remain constant since the voltage is always 120V. It does. it reads 2.334V and is unchanging. But how can I change the voltage to see if pin 14 is varying with the line voltage?

In summary:
Why does the voltage on pin 1 not change with the appliance current?
How can I change the line voltage to see if the pin 14 voltage changes?

Any suggestions?

Paul Herzmark
Berkeley, CA

[adafruit_support_bill]

The signal ground in the Kill-A-Watt unit is NOT an earth ground and directly connecting wires to the outside can mean exposing potentially lethal (to you and your Arduino) voltages

The Tweet-A-Watt project is safe as designed because the XBee module sends the data out by radio. No internal voltages are exposed outside of the case.

[pherzmar]

OK, I am convinced that it is a bad idea to run wires outside the Kill-a-Watt. Now I want to do the project with the Xbee as designed.

That still leaves the question of why the voltage from pin 1 of the LM2902N chip doesn't change with the amperage of the appliance plugged into the Kill-a-Watt. I am concerned that I have done something wrong and it won't work for the tweet-a-watt.

Shouldn't the voltage be changing?

[adafruit_support_bill]

It is curious that your voltage and current pins are reading the same down to the millivolt level (both are 2.344V). Are you sure you are connecting to the right pins?