Card Access
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Registered: Sep 2000
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Posts: 33 |
If you're interested about Power consumption and the Thinmodem, here's the basic scoop:
First of all, as far as generated heat is concerned, you'll want to read my response in a thread some time ago:
http://discussion.visorcentral.com/...?threadid=10267
As far as power consumption, let me lay some numbers on you:
Power consumption of Thinmodem while fully connected (at V.34 or V.90) = 45mA or 0.045 Amps, at 3.3V which = 150mW
For those who want a point of reference for this, consider the following:
1. A 'typical' modem (in today's technology) consumes about 150mA at 3.3V or (in energy) about 500mW. Typical 'low-power' modems consume about 100mA at 3.3V or 330mW. Low power modems worth mentioning for the HS are the Xircom and HS modems, which consume in the 100+mA range, hence the need for external batteries. You can usually see this spec on the modem's box.
2. Your Visor itself consumes about 20-30 mA while sitting ON (staring at the screen). If you happen to hold the stylus on the screen (which makes the processor work), or are doing computations or action games, the power draw for the Visor only jumps to about 70mA.
3. A Visor Prism is in an entirely different category. The backlight is extremely power hungry, and will consume on the order of 1000mW+ or 300mA! To handle this, the Prism's battery has about 2-3 times the capacity of a set of alkalines.
4. Since a modem must 'work' for the entire time it is connected (online), performing modulation and demodulation, the power draw is constant, and this is the toughest type for a set of batteries to deal with.
5. All batteries have an internal resistance which causes a bettery, regardless of how much energy it still contains, to 'sag' when it is under load. The smaller the battery, the worse the effect (generally). AAA's are SMALL batteries. This is why you'll see a recovery effect after the load is removed.
6. The power supply on the HS units also conributes to the sag factor and power consumption in two ways:
a. A load on the Springboard slot causes the 'battery gauge' circuit to overestimate the drain on the batteries.
b. Since the Visor runs on 2AAA batteries, which is always 3.0Volts or LESS, it requires a internal charge pump to pump up the voltage to 3.3V for all of the internal electronics. There is an inefficiency to doing this. So, if the SB module pulls, say 50mA at 3.3V which is 165mW, the drain to the battery might well be 80mA at 2.9V or 230mW (about a 70% efficiency). This efficiency, by the way usually goes DOWN as the batteries drain further.
7. Most people underestimate the amount of work a modem must perform. Yes, they're slow compared to a fancy DSL, etc., but a typical V.34/V.90 modem requires about 40-50 MIPS (yes MIPS) of processing power to maintain a modem connection. Your Visor, in comparison, offers about 2-5 MIPS of horsepower (not really fair to do a direct comparison), and the DSP in a modem can generally run circles around this.
8. If you want to void your Thinmodem warranty  , remove the coner and run it with the covers off. You'll note that the DSP chip will stay completely cool, while two transistors on the DAA circuit (the part that connect to the phone line) will get HOT. These parts are actually dissipating heat from MA Bell's phone line, NOT the batteries. This is normal for ALL modems and phones, but is usually unnoticed due to case sizes, etc. (See the other thread for more than you wanted to know on this).
9. Finally, drawing power from the phone line is a GREAT idea. In fact, Thinmodem does just that for a portion of the DAA circuit. This saves about 10mA of power from being drawn from the Visor batteries. We'd love to draw more, but the FCC won't allow it. Besides, phone lines would vary too much for this to be practical.
Okay, I've said enough. But a techno-geek just simply can't resist! Besides, it served as a nice break.
Have a great day!
-Card Access
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07-07-2001 04:57 AM
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