BT headsets and...

At 07:12 PM 6/2/2005, John Barnes wrote:
>However, I have a question about the assertion that Bluetooth necessarily
>requires high power consumption;
>
>How well do coin cell powered ear piece/microphone device extensions for cell
>phones work if the power consumption is such a problem?

My remarks were made comparing the power use of advertised BT chips vs 
900-MHz and 2.4 GHz RF chip sets based on what was available a couple of 
years ago.

To answer your question about headsets, I will speculate since I don't 
really know. But I'd wager a (good) beer that these guesses are pretty 
accurate. If anyone else knows more, they can chime in and correct me.

1) use lithium batteries, which are much more expensive than NiMH, 
generally too expensive for robotic use, but have better power density. All 
our cell phones use Li batteries.
2) lower bit rate. Mono phone audio only needs 64 kbits or less, vs 720 
kbits for full bore BT. This alone can provide a huge power savings.
3) lower power. Range on a headset needs to be what - 3 feet, or about 1/10 
the full BT range. Some headsets do advertise up to 10 meters of range. But 
is their battery life less at that range?
4) special power reduction modes. The headset doesn't need to be "on" 
unless a call is in progress. So they have typically 30X longer standby 
than talk time. Presumably in standby they are just listening, or sleeping 
and listening every second or so.

For wireless embedded systems, 8-240 hours of active battery life would be 
considered unusable. Systems I've been reading about try for at least a 
year of battery life, and even that is marginal.

BT was not designed with such embedded use in mind. PC peripherals and 
phones can be charged every day or few.

1000 sensors spread around a bridge or in a forest or oil field are another 
story.

Some robots could be charged every day, others not. But if you want your 
robot collecting data from battery operated sensors, you want your robot to 
use the same RF as the sensors. Currently, that would rule out BT.

Bruce