light intensity based modulator design advice desired

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Tumbleweed_Biff
 
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light intensity based modulator design advice desired

Post by Tumbleweed_Biff »

Hello,

I don't think I even qualify as a novice in this arena and I am hoping for some specific help/guidance.

Item I am trying to create: motorcycle headlight modulator
I ride a motorcycle and the biggest danger in doing so is visibility to "cage" drivers - cars, vans, etc.
A proven method of accomplishing this task is a headlight modulator which flashes the headlight back and forth from low to high beam. Per DOT requirements, it can only do so during daylight hours and at/after dusk, the light must stop modulating. There are commercial products which perform this task available for obscenely ridiculous amounts of money, starting at about $80, with most of them over $100. I know that this can be made with less than $10 of parts and not having been able to find gainful employment for an extended period of time, $80+ is a large amount of money I don't have. The problem is that I do not understand electronics and its lingo enough to figure out which parts I need and how to wire it up.

Essentially, the design is this:

12V DC in -> Bypass switch ----> Light Sensor ---> Daylight ---> Flasher relay---> 12v out ---> Low beam
l l l---> 12v out --->> High beam one cycle per second (.5 second low, .5 second high)
l l ---> Dusk ---l
l-------------------------------------------------l---> 12v out ---> Normal high/low beam switch control.

My biggest question is what the best item is to use as the light sensor: a photodiode like: http://www.adafruit.com/products/161 or would this be better: http://www.adafruit.com/products/439
Beyond that I need the idiots guide to wiring. I assume I also need some sort of switch after the light sensor that determines light/dusk dependent upon output from the sensor? Also, am I correct that 25 lumens would be a good decision point to switch between dusk and light? I saw a chart somewhere that dusk could be as low as 5 lumens, but I am don't know what DOT considers it to be ... it might be ideal to have a way of adjusting the light sensitivity level, but not if it adds significantly to the complexity or cost.

The bypass switch is simply a mechanical on/off switch that I can use externally to circumvent the modulator should the need arise (bulb out or some other malfunction).

If not obvious, it needs to be solid state and I need to be able to package it in a fairly small "water proof" package. I believe the headlights are on a 15amp circuit, but it may be 20amp.

Some of the commercial products have more advanced features such as detecting if a bulb is out and automatically switching to the working bulb and staying there, but I really don't need that degree of complexity. Other features are flashing the headlight if the horn is honked,

Thank you so much for your time and advice,
Mike

Tumbleweed_Biff
 
Posts: 3
Joined: Wed Apr 04, 2012 1:21 am

Re: light intensity based modulator design advice desired

Post by Tumbleweed_Biff »

Nuts, the posting eliminated my spaces for the diagram.

a) 12v in --> bypass switch --> off --> light sensor --> if daylight --> flasher --> 12v out --> modulate high and low beams -
cycle rate - 1/second (.5sec low / .5sec high)

b) 12v in --> bypass switch off --> light sensor --> if dusk > x >dawn --> 12v out to bike high/low beam switch

c) 12v in --> bypass switch ---> on ---> 12 v out to bike high/low beam switch.

Probably a better design would be to use the 12v output of the low beam switch into the box, so that switching to high beams automatically circumvents the modulation. If the bypass switch is on, or if it is dusk>x>dawn, then it simply skips the flasher and sends the 12v out to the low beam. That would make it so you don't have to wire to the bar high/low beam switch.

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zener
 
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Re: light intensity based modulator design advice desired

Post by zener »

This a fairly ambitious project for someone with no experience. There are a lot more issues than the light sensor. Once you did it, if you ever succeeded, you would realize that 80.00 for a finished one is a BANNED. I would suggest that this is not a good first DIY project.

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philba
 
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Re: light intensity based modulator design advice desired

Post by philba »

I have to agree with zener - a fairly big bite to chew on for a beginner. Also, be very careful about building life/safety equipment. The device failing at the wrong time could put you and others in jeopardy and insurance companies are not your friend under those kind of circumstances.

Tumbleweed_Biff
 
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Joined: Wed Apr 04, 2012 1:21 am

Re: light intensity based modulator design advice desired

Post by Tumbleweed_Biff »

I won't be by myself. I have a friend who is good at soldering and has made things before.

What is so ambitious about it? It would seem to be relatively simple: manual on/off switch, light sensor, voltage activated switch, and then a flasher

My main problem is that i don't know which specific devices will be best to use. Logic design is something I have done for years as a software developer.

I have attached a flow chart created with Diagram Designer. It really seems rather simple to me? Wherein lies the difficulty or complexity?

Thanks,
Attachments
Motorcycle Headlight Modulator.gif
Motorcycle Headlight Modulator.gif (12.44 KiB) Viewed 1549 times

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adafruit_support_mike
 
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Re: light intensity based modulator design advice desired

Post by adafruit_support_mike »

Bulletproofing it, mostly.

You're right that the basic signals aren't all that exotic, and if this were a battery-operated porch light, it wouldn't be such a big deal. In this case, the question is, "why would it be a big deal to have your bike's electrical system go wonky while you're driving down the highway in the dark?"

This doesn't just need to work, it needs to work all the time, in all sorts of weather, in an environment with lots of vibration. If it does fail, it needs to fail in a way that doesn't put your life in danger or leave you stranded until dawn. Those are the parts that take the extra work.

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philba
 
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Re: light intensity based modulator design advice desired

Post by philba »

what he said...

To amplify, you need to understand that hobbyist components are generally not designed for extended temp/harsh environments. You need really good automotive quality connectors, extended temperature range components, waterproof case (and techniques), shock mounting for the pcb. Fail safe design can be tricky. This isn't just about understanding how to solder. Personally, I've got plenty of experience and could probably do a good job on something like that but would gladly pay $80 for the peace of mind.

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zener
 
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Re: light intensity based modulator design advice desired

Post by zener »

The difficulty is in knowing which specific devices to use and how. There is a lot to this project and everyone is telling you why. You think it is easy because you admit that you know nothing about it. If you want to do it then post your proposed schematic and we will critique it. You will need the bike's electrical schematic first of course. Then once we get that squared away post what parts you would like to use and we will critique that. In the end it will have been far easier and about the same price to buy the one off the shelf. The difference is you won't have to worry about the one off the shelf. So I would say if you just want to learn stuff about it then build one. If you just want one then buy it. No one here with any sense is going to say this is a good plan for a beginner to install on the safety system of a motorcycle and then drive it around.

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