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'[EE]: Modulating a headlight'
2001\06\28@191429 by Miles McKinnon

picon face
I am building a motorcycle headlight modulator using a PIC to monitor
ambient light and a few other things.  Anyway, the PIC has to modulate the
headlight ( ~ 4Amps) at a arount 240Hz or so.

There are a few legal stipulations.  They say that you cannot switch the
ground, you must switch the +12V to the headlight.  I want to use a low Rds
HEXFET or simular transistor, but I think I would need a P-Channel device.

Is a P-Channel Mosfet difficult to drive from a TTL logic level, such as a
PIC.

Thanks for any help.

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2001\06\28@200059 by Dan Michaels

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Miles McKinnon wrote:
>I am building a motorcycle headlight modulator using a PIC to monitor
>ambient light and a few other things.  Anyway, the PIC has to modulate the
>headlight ( ~ 4Amps) at a arount 240Hz or so.
>

Miles, 240 hz is a little high, if your intent is to have
people see the flicker as a warning signal. The flicker
fusion frequency of humans is about 20 hz, so even 24 hz
may be too high. Might be good for insects however.

I think somewhere around 4 hz is the most noticeable to
humans. You might do a web search on "psychophysics".

good luck,
- dan michaels
http://www.oricomtech.com
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2001\06\28@204318 by Robert A. LaBudde

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At 08:00 PM 6/28/01 -0400, Dan wrote:
>Miles McKinnon wrote:
> >I am building a motorcycle headlight modulator using a PIC to monitor
> >ambient light and a few other things.  Anyway, the PIC has to modulate the
> >headlight ( ~ 4Amps) at a arount 240Hz or so.
> >
>
>Miles, 240 hz is a little high, if your intent is to have
>people see the flicker as a warning signal. The flicker
>fusion frequency of humans is about 20 hz, so even 24 hz
>may be too high. Might be good for insects however.
>
>I think somewhere around 4 hz is the most noticeable to
>humans. You might do a web search on "psychophysics".

Check it out on yourself, first!

This frequency can induce epilectic seizures. It's also commonly used in
inducing hypnosis. Neither of these bode well for the motorcycle driver.

================================================================
Robert A. LaBudde, PhD, PAS, Dpl. ACAFS  e-mail: spam_OUTralTakeThisOuTspamlcfltd.com
Least Cost Formulations, Ltd.            URL: http://lcfltd.com/
824 Timberlake Drive                     Tel: 757-467-0954
Virginia Beach, VA 23464-3239            Fax: 757-467-2947

"Vere scire est per causas scire"
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2001\06\28@205420 by Miles McKinnon

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240 cycles (+-40) per minute is the recommended rate:

See:
http://www.tc.gc.ca/securiteroutiere/mvstm_tsd/tsd/1080-m.htm#_Toc%20S5.6


That is a link to the Canadian law for motorcycle headlight modulators.
American law is the same.

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2001\06\28@222114 by jim

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Miles,

If you want a low RDSon, shouldn't you use an N channel device?
And I have had no problems driving a FET if I use a pullup resistor,
(or pulldown if that's what I need).

                                                           Regards,

                                                               Jim
{Original Message removed}

2001\06\29@025406 by Miles McKinnon

picon face
The reason to modulate the headlight is for visability.  If you see
something in your rearview mirror flashing at 240 cycles per minute, it will
stand out.  That makes motorcyclists safer.  This isn't a new idea.

Jim, I could use an N-Channel, but if my load is connected between source
and ground, the gate turn on voltage will be (if it is a logic level FET) ~
12V + 5V.  Without using a charge pump IC, 17V isn't available easily on a
standard automotive application.  That is the reason of a P-Channel.




{Original Message removed}

2001\06\29@055801 by jeethur

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Dan,

I guess you did'nt quite understand Miles' plans.
I guess, he wants to control the brightness of the Headlight with PWM.
And if that is the case  I suggest that Miles can go for an even
higher frequency. May be a couple of Khz. Since as a rule, the Higher
the frequency, the greater the efficency.

Jeethu Rao
http://www.jeethurao.com

{Original Message removed}

2001\06\29@074654 by Bob Ammerman

picon face
> Jim, I could use an N-Channel, but if my load is connected between source
> and ground, the gate turn on voltage will be (if it is a logic level FET)
~
> 12V + 5V.  Without using a charge pump IC, 17V isn't available easily on a
> standard automotive application.  That is the reason of a P-Channel.

That's what your PIC is for. How about a PIC12C508A.

One software oscillator to drive a voltage doubler to get the hi voltage for
the NPN FET.

Another one to blink your headlights.

Maybe even use PWM to softstart the light and reduce stress on the filament?

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

>
>
>
> {Original Message removed}

2001\06\29@090719 by Olin Lathrop

face picon face
> I am building a motorcycle headlight modulator using a PIC to monitor
> ambient light and a few other things.  Anyway, the PIC has to modulate the
> headlight ( ~ 4Amps) at a arount 240Hz or so.
>
> There are a few legal stipulations.  They say that you cannot switch the
> ground, you must switch the +12V to the headlight.  I want to use a low
Rds
> HEXFET or simular transistor, but I think I would need a P-Channel device.
>
> Is a P-Channel Mosfet difficult to drive from a TTL logic level, such as a
> PIC.

You wont be able to drive it with 0-5V when it is sitting at 12V.  However,
it should be rather easy to generate the 0 to 12V gate drive.  Most FETs
will fully switch with 12V gate drive.


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Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, .....olinKILLspamspam@spam@embedinc.com, http://www.embedinc.com

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2001\06\29@090728 by Olin Lathrop

face picon face
> And if that is the case  I suggest that Miles can go for an even
> higher frequency. May be a couple of Khz. Since as a rule, the Higher
> the frequency, the greater the efficency.

Lower frequencies are more efficient because the switching elements spend a
higher portion of the time either fully on or fully off.  You can think of
it as a fixed amount of energy lost at each switch transition.  Therefore,
the slower the rate of transitions, the lower the power loss.

The reason for higher PWM frequency is so that the load "sees" the average
on not the individual pulses.  A few 10s of Hz is sufficient for an
incandescent light bulb, a few 100Hz for most motors, but you need close to
100KHz if you are trying to produce high fidelity audio.


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(978) 742-9014, .....olinKILLspamspam.....embedinc.com, http://www.embedinc.com

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2001\06\29@092144 by t F. Touchton

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part 1 1674 bytes content-type:text/plain; charset=us-ascii
Back it down to 14hz and you can trip all the Priority Green systems here
in the US... have a green light everywhere you go!!! (and alot of other mad
drivers!!!).  Of course, this is probably illegal.

Scott F. Touchton
1550 Engineering Manager
JDS Uniphase



                   Dan Michaels
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Miles McKinnon wrote:
>I am building a motorcycle headlight modulator using a PIC to monitor
>ambient light and a few other things.  Anyway, the PIC has to modulate the
>headlight ( ~ 4Amps) at a arount 240Hz or so.
>

Miles, 240 hz is a little high, if your intent is to have
people see the flicker as a warning signal. The flicker
fusion frequency of humans is about 20 hz, so even 24 hz
may be too high. Might be good for insects however.

I think somewhere around 4 hz is the most noticeable to
humans. You might do a web search on "psychophysics".

good luck,
- dan michaels
http://www.oricomtech.com
========================

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part 2 3124 bytes content-type:application/octet-stream; (decode)

part 3 136 bytes
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2001\06\29@110231 by Dan Michaels

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Jeethu Rao wrote:
>Dan,
>
>I guess you did'nt quite understand Miles' plans.
>I guess, he wants to control the brightness of the Headlight with PWM.
>And if that is the case  I suggest that Miles can go for an even
>higher frequency. May be a couple of Khz. Since as a rule, the Higher
>the frequency, the greater the efficency.
>

Jeethu, I think he wants to modulate it at 4 hz [240 cpm],
which is a rate the human eye can perceive. He can either
turn it on and off completely at this rate, which might
shorten the life of the lamp, or modulate a high frequency
PWM at 4 hz, as you suggest, to control intensity.

- dan
================

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2001\06\29@113501 by Roman Black

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Yep, I have to throw my reliability 2 cents in here,
if you are gong to modulate a motorbike headlight,
typically a 4 amp to 6 amp 12v filament, you need
to keep it warm in the off periods. And at 4Hz it
will not turn off completely anyway as they take 0.5
sec to cool and "turn off".

My suggestion is to run the thing with some current
in the "off" period, maybe 1.5A, then bump it to the
full 4A for the "on" period. This might simplify the
circuit a bit as the semi device only has to switch
2.5A. Anyone who built a light chaser or other
incandescent bulb flasher knows the failure rate of
the bulbs if you don't keep the filament hot. :o)
-Roman



Dan Michaels wrote:
{Quote hidden}

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2001\06\29@120329 by Dan Michaels

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Roman.B wrote:
.......
Anyone who built a light chaser or other
>incandescent bulb flasher knows the failure rate of
>the bulbs if you don't keep the filament hot. :o)


And, of course, my 100W GE light bulbs always seems to
go pffffft right when I turn on the light switch. I am
sure that GE designs the cold resistance of the filaments
in such as way as to maximize the retirement payoff for
Jack Welch.

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2001\06\29@121139 by Roman Black

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Dan Michaels wrote:
>
> Roman.B wrote:
> .......
>  Anyone who built a light chaser or other
> >incandescent bulb flasher knows the failure rate of
> >the bulbs if you don't keep the filament hot. :o)
>
> And, of course, my 100W GE light bulbs always seems to
> go pffffft right when I turn on the light switch. I am
> sure that GE designs the cold resistance of the filaments
> in such as way as to maximize the retirement payoff for
> Jack Welch.


Hi Dan, yep Jinx had an excellent chart of bulb
life and voltage. I posted some calcs here a while
back showing that in 240vac countries the 60w globes
get 4x or more the startup current than in 110v countries,
and why adding a 5% volts drop resistor gives almost
infinite bulb life.

I have an incubator here, with a 100w bulb as the heater,
and it has survived months of controlled switching a
couple of times per minute to maintain temperature.
I dropped 7% across a resistor before the bulb.
:o)
-Roman

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2001\06\29@130921 by Dan Michaels

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Roman wrote:

>> And, of course, my 100W GE light bulbs always seems to
>> go pffffft right when I turn on the light switch. I am
>> sure that GE designs the cold resistance of the filaments
>> in such as way as to maximize the retirement payoff for
>> Jack Welch.
>
>
>Hi Dan, yep Jinx had an excellent chart of bulb
>life and voltage. I posted some calcs here a while
>back showing that in 240vac countries the 60w globes
>get 4x or more the startup current than in 110v countries,
>and why adding a 5% volts drop resistor gives almost
>infinite bulb life.
>

Roman, fantastic, so 5% is all it takes?

And I wonder - are the guys selling bulbs outside the US
mainly subsidiaries of american conglomerates like GE?
This would explain a lot.

- dan

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2001\06\29@131534 by michael brown

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> And, of course, my 100W GE light bulbs always seems to
> go pffffft right when I turn on the light switch. I am
> sure that GE designs the cold resistance of the filaments
> in such as way as to maximize the retirement payoff for
> Jack Welch
Part of the problem is that the vacuum "leaked out ;-D" the last time you
turned it off and it cooled, breaking the seal.  BTW I had a bulb around
here that got water in it due to a busted pipe in the ceiling and it still
lit up until the leak stopped and the bulb sucked air instead of water.
Pretty weird, huh?

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2001\06\29@132242 by Roman Black

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Dan Michaels wrote:
{Quote hidden}

Ha ha! Remember their income comes from selling
you replacement light bulbs...

I measured some 60w 240vac bulbs here, their cold
resistance was 50 to 60 ohms. You work it out! :o)
-Roman

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2001\06\29@161109 by David VanHorn

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At 12:13 PM 6/29/01 -0500, michael brown wrote:
> > And, of course, my 100W GE light bulbs always seems to
> > go pffffft right when I turn on the light switch. I am
> > sure that GE designs the cold resistance of the filaments
> > in such as way as to maximize the retirement payoff for
> > Jack Welch
>Part of the problem is that the vacuum "leaked out ;-D" the last time you
>turned it off and it cooled, breaking the seal.  BTW I had a bulb around
>here that got water in it due to a busted pipe in the ceiling and it still
>lit up until the leak stopped and the bulb sucked air instead of water.
>Pretty weird, huh?

They don't actually have a vaccum.
Argon or nitrogen I think, but there's no nothing there.

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2001\06\30@042721 by Roman Black

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David VanHorn wrote:
>
> At 12:13 PM 6/29/01 -0500, michael brown wrote:
> > > And, of course, my 100W GE light bulbs always seems to
> > > go pffffft right when I turn on the light switch. I am
> > > sure that GE designs the cold resistance of the filaments
> > > in such as way as to maximize the retirement payoff for
> > > Jack Welch
> >Part of the problem is that the vacuum "leaked out ;-D" the last time you
> >turned it off and it cooled, breaking the seal.  BTW I had a bulb around
> >here that got water in it due to a busted pipe in the ceiling and it still
> >lit up until the leak stopped and the bulb sucked air instead of water.
> >Pretty weird, huh?
>
> They don't actually have a vaccum.
> Argon or nitrogen I think, but there's no nothing there.


Low pressure nitrogen in most bulbs. It is less than
atmospheric pressure but far from a "vacuum".
Put a light bulb in a water filled container and pop
it? Should give a rough idea of the pressure inside.
-Roman

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2001\06\30@044405 by Peter L. Peres

picon face
You can use a N-VFET (cheap, easy to get) and a charge pump and level
converter to shift the 12V to something the high side mounted FET can use.
I did it that way once and it works well. The charge pump used an existing
square wave signal and a number of CMOS gates in parallel. The level
shifter was a section of a LM324 opamp wired as DC amp with gain x10 or
so. My switching frequency was 1000Hz. This was for a motor. The noise was
a welcome addition (warning noise).

Peter

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2001\06\30@060713 by Jinx

face picon face
> >> And, of course, my 100W GE light bulbs always seems to
> >> go pffffft right when I turn on the light switch. I am

> Roman, fantastic, so 5% is all it takes?

An update - it's been around 5 months since I added 47R 10W
resistors to my 240VAC wall lights, and so far not one has blown.
Based on the previous couple of years by now I would have
expected several, if not all, of them to have popped at turn on.
The ones with 2x47R resistors are only very slightly yellower but
you can't really notice that because of the shades

http://home.clear.net.nz/pages/joecolquitt/0bulblife.html

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2001\06\30@072649 by jeethur

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That sounds like a good addition to my Car.

The only question, Does it work only in the US or the whole of the World ?
Because I live in India.

Jeethu Rao

{Original Message removed}

2001\06\30@072657 by jeethur

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Hi Bob,

Is'nt 12 volts sufficient to drive the MOSFET ?

How about the PIC driving a small NPN transistor like BC548 or 2N2222
And you can connect the collector to the 12 v supply and drive the Gate
of the FET through a 10 Ohms Resistor ?

I had posted a message yesterday with a similar schematic.
Its titled "Re: [EE]: Driving a BUZ10 Mosfet"

Is there something wrong with this method ?

Jeethu Rao


{Original Message removed}

2001\06\30@074728 by Peter L. Peres

picon face
> bulb with water still working

Bulbs are not 'filled' with vacuum, but with a mixture of non-active
gases, among them Argon and Nitrogen, at low (but not vacuum) pressure. As
long as there is no Oxygen in the bulb the filament will continue to work,
but the heat losses will become enormous so it will be much dimmer. This
is not true for very small bulbs which are indeed vacummed.

Peter

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2001\06\30@100846 by Chris Carr

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> That sounds like a good addition to my Car.
>
> The only question, Does it work only in the US or the whole of the World ?
> Because I live in India.
>
> Jeethu Rao
>
Well it won't work in the UK as a different method is used which doesn't
involve light.

Chris Carr
>
>
>
> Back it down to 14hz and you can trip all the Priority Green systems here
> in the US... have a green light everywhere you go!!! (and alot of other
mad
> drivers!!!).  Of course, this is probably illegal.
>
> Scott F. Touchton
> 1550 Engineering Manager
> JDS Uniphase
>
>

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2001\06\30@102811 by Anders_Mejl=E6nder_Jakhelln?=

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I don't know if this has been suggested, but you can try to drive the P-Channel FET via Opto Coupler, and in the "off period" simply use PWM so that the filament will stay a bit warmer than turning it completely off.

Anders

{Original Message removed}

2001\06\30@152155 by George Tyler

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Be careful: Halogen light don't like to run to cold!

----- Original Message -----
From: Anders Mejlænder Jakhelln <spamBeGoneandersSTOPspamspamEraseMEJAKHELLN.NO>
To: <KILLspamPICLISTspamBeGonespamMITVMA.MIT.EDU>
Sent: Saturday, June 30, 2001 4:26 PM
Subject: Re: [EE]: Modulating a headlight


I don't know if this has been suggested, but you can try to drive the
P-Channel FET via Opto Coupler, and in the "off period" simply use PWM so
that the filament will stay a bit warmer than turning it completely off.

Anders

----- Original Message -----
From: "Miles McKinnon" <EraseMEmiles.piclistspamEraseMEhome.com>
To: <@spam@PICLIST@spam@spamspam_OUTMITVMA.MIT.EDU>
Sent: Friday, June 29, 2001 12:27 AM
Subject: [EE]: Modulating a headlight


> I am building a motorcycle headlight modulator using a PIC to monitor
> ambient light and a few other things.  Anyway, the PIC has to modulate the
> headlight ( ~ 4Amps) at a arount 240Hz or so.
>
> There are a few legal stipulations.  They say that you cannot switch the
> ground, you must switch the +12V to the headlight.  I want to use a low
Rds
{Quote hidden}

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2001\06\30@210717 by Olin Lathrop

face picon face
> An update - it's been around 5 months since I added 47R 10W
> resistors to my 240VAC wall lights, and so far not one has blown.
> Based on the previous couple of years by now I would have
> expected several, if not all, of them to have popped at turn on.
> The ones with 2x47R resistors are only very slightly yellower but
> you can't really notice that because of the shades

You could try compact flourescents.  They take much less power for the same
light output, last about 9 times longer, and they are actually cheaper.  I
knew they were more efficient and lasted longer, but I was surprised to find
they were actually cheaper when I worked it out.  It turns out the bulk of
the cost of an incandescent is the electricity it uses.  Even 9 incandescent
bulbs are cheaper than one compact flourescent, but cost much more in
electricity.  I was using $.11 per kilowatt-hour as the price of
electricity, so your milage may vary, but at that price it wasn't even
close.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, TakeThisOuTolin.....spamTakeThisOuTembedinc.com, http://www.embedinc.com

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'[EE]: Modulating a headlight'
2001\07\01@004630 by Jinx
face picon face
> You could try compact flourescents

Olin, I considered replacing filaments with fluorescents for just
the reasons you outlined. It does make sense (although some
people just don't like them). I have to admit to some out and
out bloody-mindedness with the filament bulbs - I just got so
sick of the damn things blowing I just had to try something and
"get my own back". So far the resistors have been a very good
investment

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2001\07\01@110927 by Alexandre Domingos F. Souza

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>And I wonder - are the guys selling bulbs outside the US
>mainly subsidiaries of american conglomerates like GE?
>This would explain a lot.

       Yep...GE, Philips, Sylvania, etc.


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2001\07\01@122810 by michael brown

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You all might be interested in this info.  http://www.kisantech.com has headlamp
modulators and they claim to use a P-channel mosfet using current regulation
for the modulation.  150 watts maximum.  It's a very small package that
modulates current between 100% and 13% (I guess so the filament doesn't cool
too much)  It also has a light sensor to deactivate the modulation upon
entering a tunnel or darkness.  Pretty neat product, but cost's way too
much. $100.00 for single bulb setup.

You might also be interested in the tireAlert pressure monitoring system.
Uses unpowered device that is attached to the wheel to sense tire pressure.
They claim 1 psi accuracy.  I think that you would have to have the tires
rebalanced after installation.

Any ideas on how the unpowered sending unit functions?  I'm guessing some
kind of internal coil or LC resonant tank.

There's a pretty good market for these kinds of "gadgets".  Bikers love to
spend money on bike toys.  Toys that help you to be seen are very popular.

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2001\07\01@124050 by Spehro Pefhany

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At 11:25 AM 7/1/01 -0500, you wrote:
>You all might be interested in this info.  http://www.kisantech.com has headlamp
>modulators and they claim to use a P-channel mosfet using current regulation
>for the modulation.  150 watts maximum.  It's a very small package that
>modulates current between 100% and 13% (I guess so the filament doesn't cool
>too much)  It also has a light sensor to deactivate the modulation upon
>entering a tunnel or darkness.

If you read the relevant standard that someone posted a link to, the
light sensor is a required feature. It must also have a way of bypassing
the modulator (presumably a mechanical switch) in case of failure.

Best regards,


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2001\07\01@142218 by Bob Ammerman

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To bring this thread closed to where it started...

While playing with me son with his model railroad I noticed the unusal
headlamp modulation on the locomotive. It uses what is called a MARS light
which alternates between a left and a right filament and appears to shift
back and forth.

Something like this on a motorcycle would certainly be noticed by day (and
then perhaps just turn on both at night.)

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\07\01@145116 by Chris Carr

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> >And I wonder - are the guys selling bulbs outside the US
> >mainly subsidiaries of american conglomerates like GE?
> >This would explain a lot.
>
>         Yep...GE, Philips, Sylvania, etc.
>
>
Actually the headquarters of Philips is not in the United States of America
but in the United States of Socialist Europe, to be more precise Holland. So
it's a European not an American Conglomerate.

8-)

Chris Carr

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2001\07\01@210423 by Robert A. LaBudde

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At 07:48 PM 7/1/01 +0100, Denis wrote:
>Actually the headquarters of Philips is not in the United States of America
>but in the United States of Socialist Europe, to be more precise Holland. So
>it's a European not an American Conglomerate.

I thought, as Hercule Poirot might have said, "It's a Belgie, not a Dutchie!"

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2001\07\01@222427 by Russell McMahon

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> > >And I wonder - are the guys selling bulbs outside the US
> > >mainly subsidiaries of american conglomerates like GE?
> > >This would explain a lot.
> >
> >         Yep...GE, Philips, Sylvania, etc.
> >
> >
> Actually the headquarters of Philips is not in the United States of
America
> but in the United States of Socialist Europe, to be more precise Holland.
So
> it's a European not an American Conglomerate.


Excuse the probably incorrect spelling - it was (is?) "Philps Gloeilampen
Fabriken" so the link to lightbulbs is a time honoured one.

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2001\07\02@132831 by D. Schouten

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> > Actually the headquarters of Philips is not in the United States
of
> America
> > but in the United States of Socialist Europe, to be more precise
Holland.
> So
> > it's a European not an American Conglomerate.
>
>
> Excuse the probably incorrect spelling - it was (is?) "Philps
Gloeilampen
> Fabriken" so the link to lightbulbs is a time honoured one.

'Philips Gloeilampen Fabrieken'. Philips HQ is in Eindhoven The
Netherlands. Although I'm quite sure the lightbulbs aren't
manufactured in The Netherlands anymore (only special products) due to
high production costs. I know Philips makes lightbulbs in France and
Eastern Europe.

Daniel... (from Philips land :-)

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'[EE]: Modulating a headlight'
2001\09\02@201431 by Spehro Pefhany
picon face
At 03:27 PM 6/28/01 -0700, you wrote:

>Is a P-Channel Mosfet difficult to drive from a TTL logic level, such as a
>PIC.

It will be "off" when the gate voltage is at 12V (13.8V), so you can drive it
easily with an open-collector driver (eg. 2N4401) with a base resistor and a
pullup resistor. You may want to use a zener from source to gate and an
additional
series resistor to prevent punchthrough of the gate oxide on spikes in the
supply voltage.

Best regards,

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2001\09\02@233636 by Gennette, Bruce

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Sorry to put a dampener on you all but technology is a-changin'

The 'next generation' of headlamps (already available on some models) are
short arc lamps in tiny tubes operating at 36 volts or so.  They have
drivers in their bases to create the startup and run voltages/currents from
12V.  They even compensate for 'aging' by adjusting the inputs over time.

They *DO NOT* like to be restarted hot nor ramped up and down.

The 'next generation' of vehicles are going to operate with 36 volt
batteries (alright 42 volts fully charged) to keep the size of voltage
losses, cables and electric motors down.  Many 12V appliances will still be
used on a legacy 12V circuit that will be avaliable, but a lot of devices
will be changing over to 36V (headlamps certainly).

So be prepared.  Do your homework; it may be worthwhile developing a device
for older style headlamps (after all there are a lot of them), but it also
may not be worth it.

Bye.

{Original Message removed}

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