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Survey : Weight vs. battery life for bike computer?



 
 
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  #1  
Old July 10th 03, 06:39 AM
Doug
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Default Survey : Weight vs. battery life for bike computer?

On Tue, 08 Jul 2003 20:42:12 GMT, "Cleanbean"
wrote:

I'm working on designing a "next generation" bike computer. We're
trying to figure out what would be the optimal tradeoffs for the
batteries. We are looking at the following options (With


I wouldn't use a computer with the weight of a AAA or AA. Consider using 2
large watch type batteries.


Funny how non-engineer types so blithely recommend something. I got a
real kick out of this one.

Doug
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  #2  
Old July 10th 03, 06:39 AM
Doug
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Default Survey : Weight vs. battery life for bike computer?

On 8 Jul 2003 16:02:56 -0700, (Reza Naima) wrote:

Another option is to go with an optional 1 or 2 battery design. The
DC-DC voltage converter will work with voltages as low as .85 volts.
Thus, we can put the space in the device and let the consumers decide
if they want to have 1 or 2 batteries inside it.


Nice option.

A final option is to reduce the sampling rate. This can be configured
on the fly to give the user control over battery life.


Nice too.

Our calculations are for one sample per second. By going to one
sample every 2 seconds (gps only), then we can greatly increase
the power while sampling other metrics at higher rates.


What about adaptive GPS sampling rates? The idea of adding more
features makes the project more fun to do, so of course I'd like that.
But seriously, wouldn't it be cool to simply read the speed off the
cyclocomp and adjust the sampling based on that? Of course zero speed
and low speeds can quickly turn to high speed on a bike, so tests
would need to determine what rates in those areas. But that's what
engineering for power saving is all about, so hey.

Or are you planning to derive speed from GPS? As a user, I'd worry
about accurate speed readings in that case, due to signal lock loss.
Have you considered some field tests to see if 1 sec sampling is
overkill? I've never used GPS while cycling, so I can't say what 1
sec sampling would do. I'd think you need to look at the data to see
what sampling rate gives a good course profile. At the speeds bikes
travel, I can't guess. A twisty road, darting around city blocks, and
up and down canyon roads would all be interesting to see in GPS data
at bike speeds.

1) What is the maximum weight you would accept for a device like the
one Doug mentioned below?


this is a GPS/HRM/cyclocomp with a dot matrix LCD? Good luck with it.


I'd have to weigh my current separate units and go from there. If a
combo unit weighed roughly the same or less I'd be happy. But really,
I'd consider GPS for low speed touring, mountain biking, or training
with the need to have heart vs. climbing info. In those 3 cases,
weight would not be a prime consideration.

2) What is the maximum you would be willing to pay?


There are other considerations for me. I prefer separate units
because I use them for other activities. My wris****ch HRM gets used
in the gym and on runs, a GPS gets used on hikes and while driving,
and the cyclocomp is perpetually mounted. An all-in-one would have a
strike against it in my book for that reason. I also like being able
to replace a failed unit separately. Losing the cadence feature in an
all-in-one due to a balky pickup would be aggravating to no end, and
worrying about getting future replacement parts instead of replacing a
whole unit is troubling. But maybe that's just me. I know a lot of
people like the idea of combining gadgets. I for one would not buy a
combo DVD-VCR for example.

But assuming it had kick butt features, like data download, a dot
matrix LCD display with gobs of info (I'm a sucker for dot matrix
LCDs, played with a 640x200 for my senior EE project), high end HRM
functions with data storage, and cadence for the cyclocomp, I'd pay
what 3 separate units of comparable features cost. If the LCD went
further and showed all sorts of data, like altitude, graphical ride
profile over the last x distance, current HR, avg HR over the last x
minutes, cadence, speed, avg speed, speed over waypoints, HR over
waypoints, distance, ride time, clock, etc, with possibly a fully user
configurable display to move fields, make things bigger/less info,
smaller/more info, well, then I'd be sorely tempted just for the play
factor. You did say "next gen" after all. But I practically
described the display a PC would give analyzing the data, so perhaps
that's unrealistic.

3) What would you like to pay?


Depends what my income is. It'll be going down in the coming 2 or 3
years, so that's a good Q. I wouldn't buy a gadget like this at this
time. I just got a new HRM and cyclocomp.

What processor is driving all this? How many pixels in the LCD?
Programming in assembly? How much code? Tell us more. This is great
stuff, where fun and enjoyment of a passion (cycling in this case)
meet the nitty gritty of engineering.

Doug
  #3  
Old July 10th 03, 01:02 PM
Jasper Janssen
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Default Survey : Weight vs. battery life for bike computer?

On Thu, 10 Jul 2003 05:39:58 GMT, Doug wrote:
On 8 Jul 2003 16:02:56 -0700, (Reza Naima) wrote:


Or are you planning to derive speed from GPS? As a user, I'd worry
about accurate speed readings in that case, due to signal lock loss.


Ooh, Shiny! I just got an idea: If you have GPS anyway, and a wheel-rev
counter, you can derive the wheel diameter automatically. A few miles in
should be enough to get at least as close as regular bike comps will, and
if conditions change (say, you let your tire go flatter or a bigger rider
is on) it adapts to that. Dunno if it's computationally feasible, though.
Probably is. Just every mile or so (either GPS indicated or revcounter
indicated) adjust the wheeldiameter value to match the two. Though there
is one problem I can see: If you're, say, doing circles in a parking lot,
the GPS, especially at multiple seconds sampling rates, won't be accurate
at all. The same goes for if you round a corner: the GPS trail will take
the straight diagonal from last-point-before-corner to
first-sample-after-corner, whereas you would have had to go around.
Perhaps you should just have it as a special "calibrate wheeldiameter now"
function to be used in initial setup with a long (nearly) straight piece
of road, in addition to the option of setting wheeldiameter manually.

For the shinyness factor, flightdeck style gear indications are of course
also cool. I wonder if you could make your computer compatible with a
flightdeck wiring harness? That'd give you cadence and wheelrev sensors as
well as (perhaps most importantly and very hard to do any other way) gear
sensors and a couple of control buttons in a useful place, if I remember
that wiring harness right. Dunno if that's either practically or legally
feasible, though, they probably have patents. Ask your lawyer.

factor. You did say "next gen" after all. But I practically
described the display a PC would give analyzing the data, so perhaps
that's unrealistic.


Well, I dunno what chip they're gonna use, but with their energy budget
they should have room for one hell of an embedded risc CPU. Certainly on
the level of what a Palm uses, possibly on the level of a PocketPC, even.
With that kind of processing power, what you just said should almost all
be eminently feasible IMHO, up to at least the display resolution of a
Palm or pocketPC screen. Various numbers and average of them over last x
minutes should be trivial, grahical ride height profile, well, slightly
less trivial but should be doable just the same. GPS style mapping would
probably be fairly hard, mostly for storage space reasons. OTOH, painting
your trail on the map should again be trivial compared to doing the map
itself.

The user configurable screen layout would probably be best done with the
associated PC software -- like the Philips Pronto universal remote
controls.

What processor is driving all this? How many pixels in the LCD?


Indeed. If you wanna do it for a shoestring price, you might need to
consider using LCDs from other massmarket appliances and developing your
own driver hardware if that's not usable. The cost there is that
development costs go way up. Graphical LCDs in the black/white 128x64
pixel format are available pretty cheaply, but relatively small (as a
direct relationship, of course).


Jasper
  #4  
Old July 10th 03, 01:05 PM
Jasper Janssen
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Default Survey : Weight vs. battery life for bike computer?

On Thu, 10 Jul 2003 05:39:58 GMT, Doug wrote:
On Tue, 08 Jul 2003 20:42:12 GMT, "Cleanbean"


I wouldn't use a computer with the weight of a AAA or AA. Consider using 2
large watch type batteries.


Funny how non-engineer types so blithely recommend something. I got a
real kick out of this one.


My cyclocomp does just fine on one large watch type battery, for years on
end. This seems to be a simple case of a misunderstanding of the type of
device being discussed (which isn't hard to do from the opening post),
rather than any profound misunderstanding.

So don't be a selfrighteous prick about it.

Jasper
  #5  
Old July 10th 03, 03:45 PM
Nick Burns
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Default Survey : Weight vs. battery life for bike computer?


"Cleanbean" wrote in message
.. .
I wouldn't use a computer with the weight of a AAA or AA. Consider using

2
large watch type batteries.

John in Texas


Why? You don't even know what features it would have. I suppose the original
article should have at least hinted at what was on offer for the proposed
costs. I did not answer because for me it would really depend on what I am
getting. I would like to see a modular system. The disply could be designed
like the SRM head unit and it could have some kind of open standards bus to
add on peripherals. Let's say you have something comparable to the 710 but
with a superior pixelated display. The add ons could incluse power from any
of the systems currently available (or at least more than one). A GPS unit
could be added for certain applications and otherwise left at home.



"Reza Naima" wrote in message
om...
I'm working on designing a "next generation" bike computer. We're
trying to figure out what would be the optimal tradeoffs for the
batteries. We are looking at the following options (With
non-rechargeable batteries you can get 2x the performance):

1 AAA NiMh Rechargeable Battery : 2 hours, 12 grams
2 AAA " : 5 hours, 24 grams
1 AA " : 4.5 hours, 27 grams
2 AA " : 10 hours, 34 grams


Note that the product is designed to store ride information to be
downloaded to a PC. Thus you would want the batteries to last the
entire trip. However, you could always carry extra batteries with you
in a separate pouch for extended trips.

Let me know what you think...
Reza





  #6  
Old July 12th 03, 10:56 AM
Reza Naima
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Default Survey : Weight vs. battery life for bike computer?

Let's say you have a reasonable NiMh AA cell, say 1600 mah.
You have to draw 180 ma to run it down in 10 hours. That's
a lot of current.


1600mah at 1.2volts. Most electronics want 3.3v, so you're looking at
581mah at 3.3v, which at a burn rate of 150ma comes to 3.8 hours based
on our initial calculations. Since then, we've started doiong some
measurements, and we're looking at a more reasonable 70-80mah
including the LCD display. This doubles the expected time to ~8 hours
which we think is sufficient for most riders.

The big catch is that enthusiasts with high disposable income
will view this as too heavy. An easy fix is to have an initial
version with 2 D cells. Then switch to AA's and advertise "xx grams
lighter."


True Or, we can post the device weight w/o batteries and state it
as such.

Seriously, you need to budget power way better. Where is it all
going? Are you using a linear regulator?


Into the FLUX CAPACITOR!! I did mention the device is capable of time
travel, right? We've made improvements from the 1.31 gigawatts
required

More seriously, a DC-DC voltage converter. Linear regulators can only
reduce voltage.


And finally, if you use USB for PC downloads you can sponge off of USB
power and save or recharge the internal batteries.


And that was the design before we consulted FCC regulations. Seems
that it becomes much more complicated once it is attached to a PC.
Having removable flash makes it save us lots of time and money in FCC
testing. Plus, the smallest flash size is 32Megs!! That's a lot of
data you can save!

A future version might include a camera to snap a picture every so
minutes. And the device is designed to be expandible via a
multi-master bus system.

So, who wants to buy some vapour-ware now? If not now, check back
around xmass-time...

Reza


New Question : if the device could have any one "cool" feature, what
would it be?
  #8  
Old July 14th 03, 04:28 PM
Lindsay
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Default Survey : Weight vs. battery life for bike computer?

On Mon, 14 Jul 2003 10:56:58 -0400, archer
wrote:

In article ,
says...

...

New Question : if the device could have any one "cool" feature, what
would it be?


The ability to import your ride data into one of those PC mapping
programs, and plot your times and average speeds along the displayed map.


And the ability to show you sprinting from the Yellow Jersey group at
the end of the ride to leave them in your dust. Even though your ave
MPH is only 18.5!! ;-)

Lindsay
----------------------------
"One of the annoying things about believing in free
will and individual responsibility is the difficulty
of finding somebody to blame your problems on. And
when you do find somebody, it's remarkable how often
his picture turns up on your driver's license."

P.J. O'Rourke
 




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