Serial port for Kill A Watt - Tweet A Watt compatible

[kshyamchandar]

d

[oPossum]

ADC conversion time is 2 microseconds.

There are two samples (voltage and current) taken every 984 microseconds.

Timer2 is configured to increment every 8 microseconds, and the Timer2 preset is 123.
So, the Timer2 interrupt flag will be set every 8 * 123 = 984 microseconds.

[kshyamchandar]

d

[kshyamchandar]

d

[oPossum]

It is logic level serial, so a USB to logic level (3.3V or 5V) serial cable like this is required. Do not use a USB to RS-232 cable.

[wukongnyc]

I am trying to make Xbee based Tweek A Watt and brought all the components needed. I have the same issue that Kill A Watt device that I brought recently (2012) has different board than the original instruction, it seems event different than the one in this thread, but it seems that originator of this thread suggest using optisolator that will make the solution independent of varieties of board. I am new to electronic components/circuits. My questions are:

1) what is optisolator? what are the key functions of it?
2) where I can get one to build the solution as suggested here? are there different types of optisolator?

[adafruit_support_rick]

An optoisolator essentially uses LEDs to transmit signals from one electrical circuit to another, such that the two electrical circuits are isolated from each other.

The OP was using this optoisolator device:
http://www.fairchildsemi.com/ds/6N/6N138.pdf

[satu1991]

For the serial cable, do we have to connect Tx to serial data & Gnd to Ground.