Headlamp modulator scheme

Electrical issues
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haggis
Posts: 158
Joined: Fri Mar 19, 2004 3:35 am
Location: Maine USA

Headlamp modulator scheme

#1

Post by haggis » Thu Jan 15, 2004 2:52 am

kell,
have you got a stashed away anywhere?
Cant find the one I thought I'd saved..thanks, Haggis



kell
Posts: 369
Joined: Sat Jun 19, 2004 2:58 am

Re: Headlamp modulator scheme

#2

Post by kell » Fri Jan 16, 2004 1:38 am

I searched google and found an explanation of the law:
http://www.hydra-glide.com/docs/49CFR_s ... S7.9.4.pdf" onclick="window.open(this.href);return false;
looks like for a modulator that's completely legal you'd almost need a commercial unit.
I've never built a circuit to flash the headlight. You could use a regular flasher unit, but according to that link you need 240 cycles per minute (federal law). Could be done with a 555 timer chip I guess. I haven't made a study of the legal requirements, just took a quick glance at that website.
Was just looking at a website the other day with a sort of tutorial about how to use the 555 timer, since I haven't used one in a circuit yet (although I got one with my last order of parts). Will try to post the link later.

kell
Posts: 369
Joined: Sat Jun 19, 2004 2:58 am

Re: Headlamp modulator scheme

#3

Post by kell » Fri Jan 16, 2004 2:19 am

You could set the frequency and duty cycle, and use it to trigger a power mosfet or the like. I think there's a requirement in the law that you have a light sensor to turn the modulation off automatically at night. They would have to throw a requirement like that in there, PITA.

haggis
Posts: 158
Joined: Fri Mar 19, 2004 3:35 am
Location: Maine USA

Re: Headlamp modulator scheme

#4

Post by haggis » Sat Jan 17, 2004 1:13 am

Kell,
thanks for the help. the 555 timer I'm familiar with...kinda reminds me of the flip-flops we used to build back in 74LS land... think i can figure something out with MOSFETS. I read up on the law too...seems like you do need some kind of ambient light over ride.
Would look real cool on the hotrod ...definitely see it coming!! Haggis

kell
Posts: 369
Joined: Sat Jun 19, 2004 2:58 am

Re: Headlamp modulator scheme

#5

Post by kell » Sun Jan 18, 2004 2:29 pm

This should make it easier: http://www.buchanan1.net/modulator.shtml" onclick="window.open(this.href);return false;

I just typed "headlight modulator" into google, and that came up first.
His circuit has two timers. The modulator circuit is not supposed to turn the filament all the way off according to the regulations. So one of the timers has a rapid on-off duty cycle that has the effect of dimming the filament. The other timer accounts for the visible modulation of the light. Per regulations, the modulator only acts on one filament. And you're not supposed to put it in the ground connection, apparently for that reason. Buchanan did, but it's a simple matter to tie any circuit grounds together and isolate them from the chassis so as to be able to wire it in the hot side of one of the headlight filaments.
The regulations also state that you must have a light sensor (like the photosensitive eye on an outdoor light or streetlamp) that will turn the modulator off automatically at night and they specify the light level it has to react to in lux or candles or something. Like nobody has the smarts to flip a switch at dusk. That's the biggest PITA about this in my opinion. I didn't really take a good look at the buchanan circuit but it may not have that electric eye. However I think the fella that sent in an improved circuit to that website with mosfets instead of bipolar transistors also might have put a photosensor in.
But the thing to worry about is cops. Most of them probably don't know squat about headlight modulators and you don't want a tik, so you'd want to carry a copy of the law.

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