Have you ever wondered how much power different operations on your Duo consume? How much battery life you really gain by dimming the screen? How much extra power the modem uses? This program will help you answer those questions.
This started out as a simple little background window that showed two interesting items: the battery voltage (in volts) and the power consumption (in watts). But then I got totally carried away and added a detailed information window that tells you just about everything you might ever want to know about the Duo power system...
The heart of this program is the extended Power Manager, currently only found in the Powerbook Duo computers. Besides monitoring battery voltage, the extended Power Manager monitors actual power consumption and a wealth of other data.
Most of the items in the Detailed Power Information window are self explanitory. The one non-obvious item is "Usage." This is a power consumption counter maintained by the Power Manager, incremented as fixed amounts of power are consumed from the battery. When the Power Manager has seen a battery charge fully, it sets the counter to zero. The theory is that each battery stores so much power, so by watching this counter, you can accurately tell how much power you have left at any time. In practice, it doesn't work so well, for a number of reasons. If you charge a battery externally, the Power Manager can't tell it's at full charge when you insert it, so the counter isn't zeroed. Similary, if you remove a battery, then immediately reinsert it, the Power Manager doesn't know if maybe you really did discharge it some, so invalidates the counter. Finally, the total amount of power available from a battery varies between batteries, and also depends on temperature during consumption. But the usage counter is still useful, especially if you always charge a battery in the Duo.
Battery ID is a serial number stored within the battery itself, and unique for each battery (it is not releated to the serial number printed on the battery).
A couple of icons are displayed for various operating states. They are displayed in place of the "power" value in the voltage/power window when the Duo is plugged in.
Battery is charging:
Duo is plugged in:
Battery is dead (won't charge):
The data is updated every 5 seconds, but you can change this rate through the "Set Update Rate" dialog. Since the power and voltage measurments are averaged through a sliding 8-second window by the Power Manager, there's no need to update any faster, but you might want to slow it down.
Power is only displayed when operating off of a battery (i.e. not plugged in).
You can change the maximum and minimum limits of the voltage and power graphs through the "Set Graph Limits" dialog.
The state (open or closed) and the position of the two windows is stored, along with the update rate and graph limits.
If you have any other battery utilities, you may notice that they report a much lower battery voltage than DuoMon. This is because the Power Manager doesn't return an absolute voltage, but rather a percentage between two limits. The limits that Apple published in Inside Mac volume 6 are valid for the PB-1xx series, but are incorrect for the Duos. The voltage that DuoMon reports is the correct value. (Note to developers - the limits for the Duo are 7.0 through 22.0).
Drop me a line if you find this program useful or interesting. Let me know what features you'd like to see. Also, let me know where you found this.
Mike Blackwell
The Robotics Institute, Carnegie Mellon University
