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'[PIC] Bike Light Design'
2006\06\07@001627 by scott larson

picon face
Hello All,
Riding my bicycle home tonight, I decided I ought to make a bike light
controlled by a little 10F pic. I have a 9.6V NiMH rechargable battery
that I think would be perfect for the job, and I'll get some super
bright LEDs, but i wasn't sure how to best regulate the voltage (LDO?
something more efficient?) to the PIC or how to best control the LEDs
(pwm?). I think I need about 5 white LEDs for a "continuously on"
headlamp, and 4 or 5 red LEDs for a flashing tail light.
Should I charge up capacitors for the LEDs or something else??

I'm just an undergraduate, thus I don't have much experience in
designing things like this.
Any and all suggestions would be appreciated.

Thank you,

Scott Larson
1136 W. Oakdale Apt. 1
Chicago, Il, 60657
619-400-9775
http://goldscott.com

2006\06\07@023508 by Jinx

face picon face
Hi Scott,

I would have suggested something like the S81250 or
LP2950CZ5.0, as here

(16F88-based, a very high power bike lamp indeed)

http://home.clear.net.nz/pages/joecolquitt/luxeon_lamp.gif

from

http://www.siliconchip.com.au/cms/A_106372/article.html

s/w is downloadable from elsewhere on the site

Because of the generous overhead betwen battery voltage and 10F,
the parameter you'd be looking at would be quiescent current, rather
than LDO

I've used white LEDs for a bike lamp

http://home.clear.net.nz/pages/joecolquitt/bikelamp.html

and prefer them flashing. You do stand out more. Red rear lamp
is particularly more noticeable when flashed, compared to other
vehicles' non-flashing. For mine I used a basic bistable

http://www.play-hookey.com/digital/experiments/rtl_bistable.html

Companies like Maxim and Philips have a range of white LED
drivers too. These include DC-DC converters so that you can
run them off of just one or two cells

2006\06\07@024409 by Jinx

face picon face
Scott, my apology. I referred to a bistable in previous post. I got
sidetracked on the page and meant astable

http://www.play-hookey.com/digital/experiments/rtl_astable.html

2006\06\07@075805 by Gerhard Fiedler

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Jinx wrote:

> (16F88-based, a very high power bike lamp indeed)
>
> http://home.clear.net.nz/pages/joecolquitt/luxeon_lamp.gif

Is there a purpose in the fuse F2 being between one cell and the other
three? It looks purposeful, but I can't really see one.

Gerhard

2006\06\07@083018 by Jinx

face picon face
> > home.clear.net.nz/pages/joecolquitt/luxeon_lamp.gif
>
> Is there a purpose in the fuse F2 being between one cell and the
> other three? It looks purposeful, but I can't really see one

AFAICS F2 isn't mentioned in the Part 1 text, which covers the
technical/how-it-works. Although, as luck would have it, I can't
find my May issue, which has the constructional details and may
refer to F2. I wanted to find it anyway to pass on the windings
of the step-down transformer T1, based on an FX2240 pot
core/bobbin, as is L2

If you go to April 2006 of Silicon Chip's download page

http://www.siliconchip.com.au/menu_1701/cms/attachments/index.html

you can download the .hex and .asm for the project. The asm is
commented and will give you some idea of the capabilities and
functions of the driver circuit

2006\06\07@084300 by Spehro Pefhany

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At 08:57 AM 6/7/2006 -0300, you wrote:
>Jinx wrote:
>
> > (16F88-based, a very high power bike lamp indeed)
> >
> > http://home.clear.net.nz/pages/joecolquitt/luxeon_lamp.gif
>
>Is there a purpose in the fuse F2 being between one cell and the other
>three? It looks purposeful, but I can't really see one.
>
>Gerhard

Obviously there is no electrical difference in the circuit as shown, since
the four are all in series. No difference under fault conditions seems
likely. So maybe it's a mechanical issue.

I don't have the article, but I am imagining a battery holder with two
links to connect the three C cells together, and wires or a snap coming
off the remaining two connections. Now replace one of the links with a fuse.

>Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
spam_OUTspeffTakeThisOuTspaminterlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
->>Test equipment, parts OLED displys http://search.ebay.com/_W0QQsassZspeff


2006\06\07@091909 by M. Adam Davis

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On 6/7/06, Gerhard Fiedler <.....listsKILLspamspam@spam@connectionbrazil.com> wrote:
> Jinx wrote:
> > http://home.clear.net.nz/pages/joecolquitt/luxeon_lamp.gif
>
> Is there a purpose in the fuse F2 being between one cell and the other
> three? It looks purposeful, but I can't really see one.
>
> Gerhard

Thermal fuses in rechargable battery packs are wired this way.
Rechargable battery packs (that I've seen for nimh and nicd) don't
typically have current fuses, since you may need to pull several amps
from a pack.  Li-Ion packs usually have several forms of protection
since overcurrent conditions can result in a volatile situation
immediately.  NiCad and NiMH are much more tolerant to over current
conditions.

Still, the thermal fuse acts as a slow current fuse since drawing too
much current (or charging too much) for too long will overheat the
pack and open the fuse.

By placing it between two batteries in the schematic it is explicit
that it be placed in the pack rather than relegated to a seperate
board where it would be ineffective.

The fuse is marked as a current fuse though, so I too am curious about
the designer's intent.  Either they knew a fuse of some sort went
inbetween the cells, and picked a current fuse suitable for their
project, or they aren't specifying that the fuse is also a thermal
fuse.  If it only reacts to current, then it doesn't need to be
inbetween the cells.

-Adam

2006\06\07@093104 by Peter

picon face

Jinx <joecolquitt <at> clear.net.nz> writes:

> http://home.clear.net.nz/pages/joecolquitt/luxeon_lamp.gif

Is that circuit fairly efficient ? Also, the voltage/current metering device
using Q3 and Q4 looks like it would introduce the Vgs of the open 2N7000s in
series with the measured voltage. No ?

Peter



2006\06\07@104438 by scott larson

picon face
Thank you Jinx for the links your provided. The circuit from Silicon
Chip is a bit more complicated than what I want to do, but I'll try
out an astable multivibrator.



On 6/7/06, Peter <plpspamKILLspamactcom.co.il> wrote:
{Quote hidden}

> -

2006\06\07@112508 by Dwayne Reid

flavicon
face
At 07:30 AM 6/7/2006, Peter wrote:

>Jinx <joecolquitt <at> clear.net.nz> writes:
>
> > http://home.clear.net.nz/pages/joecolquitt/luxeon_lamp.gif
>
>Also, the voltage/current metering device using Q3 and Q4 looks like
>it would introduce the Vgs of the open 2N7000s in
>series with the measured voltage. No ?

Assuming (from the voltage divider ratios) that the voltage at AN2 is
less than 3V and given that Vgs for a 2n7000 is less than 2V (1.3V
for some variants), there should be no problem.  This also assumes
that the voltage drop across the current sense resistor is low enough
that the body diode of the inactive 2n7000 does not conduct.

It actually looks like a competent design.

dwayne

--
Dwayne Reid   <.....dwaynerKILLspamspam.....planet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax

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2006\06\07@162443 by Peter

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On Wed, 7 Jun 2006, Dwayne Reid wrote:

> At 07:30 AM 6/7/2006, Peter wrote:
>
>> Jinx <joecolquitt <at> clear.net.nz> writes:
>>
>> > home.clear.net.nz/pages/joecolquitt/luxeon_lamp.gif
>>
>> Also, the voltage/current metering device using Q3 and Q4 looks like it
>> would introduce the Vgs of the open 2N7000s in
>> series with the measured voltage. No ?
>
> Assuming (from the voltage divider ratios) that the voltage at AN2 is less
> than 3V and given that Vgs for a 2n7000 is less than 2V (1.3V for some
> variants), there should be no problem.  This also assumes that the voltage
> drop across the current sense resistor is low enough that the body diode of
> the inactive 2n7000 does not conduct.
>
> It actually looks like a competent design.

I would use a tc66 gate to do this or two mosfets back to back. Maybe it
works as shown but I would be worried about reverse leakage and such
when a mosfet is closed.

Peter

2006\06\07@184217 by Jinx

face picon face

> Thank you Jinx for the links your provided

You're welcome. Russell posted a link for LED circuits earlier
this week. Quite a few LED flashers

http://www.hobbyprojects.com/L/LED_(Light_Emitting_Diodes)_Circuits.html

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