# Constant brightness how to needed



## tkruger (Jan 18, 2009)

I run Athearn Blue Box locos for the most part. Does anyone have a simple materials list and wiring diagram to make a light that remains at the same brightness regardless of the throttle position? I would like to use grain of wheat bulbs as I have allot of them currently.


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## gunrunnerjohn (Nov 10, 2010)

Well, I recently found some neat 20ma constant current sources that will handle up to 90V, which should make them more robust.

Mouser has them for .44/ea. They're the top ones on this page: http://www.mouser.com/Search/Refine.aspx?Keyword=689-CL2N3-G The data sheet is available on the same page in the description.


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## NIMT (Jan 6, 2011)

That easy Tim It called DCC :laugh::laugh::laugh: Sorry could not resist!
Here is one way to do it.


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## gunrunnerjohn (Nov 10, 2010)

Sean, that's an interesting idea for the lighting, I've never seen that suggested before.  It does siphon power away from the max speed of the engine, not sure if this is an issue or not. One other issue is the lights go out when you stop the locomotive...

Tim, did I mention that you can parallel those constant current chips for more current?


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## T-Man (May 16, 2008)

Sean. I don't think the circuit runs to the motor but off one motor lead. If you know what I mean? Plus three diodes per light( ebay in bulk).

That mouser chip will work. For 44 cents ! Four to eight LEDs per coach.
I would run an on board power supply for 12 bucks. That's a cost saver!!


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## NIMT (Jan 6, 2011)

T-man I totally agree! After relooking at what I gave him to look at, it's not the best choice at all!:thumbsdown:
The only problem that I see with the CL-2 is that the bottom voltage is 5 volts, you could compensate this with 4 AAA rechargeable batteries on a charging circuit, and a voltage comparator to turn it on at .5 volts or greater and off .3 volts and lesser.


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## gunrunnerjohn (Nov 10, 2010)

Well, since I deal in O-gauge, if the train is running, we see more than 5V.  In addition, I'm running TMCC, so I always have 18VAC available.


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## tankist (Jun 11, 2009)

frankly i don't see the variable brightness as big issue compared to the kind light itself - cabfryer. to start off it should be made into normal headlight fisrt, then we can start talking brightness.


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## tkruger (Jan 18, 2009)

tankist said:


> frankly i don't see the variable brightness as big issue compared to the kind light itself - cabfryer. to start off it should be made into normal headlight fisrt, then we can start talking brightness.


I am attempting to get all the parts in place first and then add it all at once. I an Athearn BB F7 I too a piece of cardboard and placed it in the cab so only the light shows through the two headlights. I plan to do something simular with my DD40 but would use two lights, one for the number boards and one for the nose light. 



> T-man I totally agree! After relooking at what I gave him to look at, it's not the best choice at all!
> The only problem that I see with the CL-2 is that the bottom voltage is 5 volts, you could compensate this with 4 AAA rechargeable batteries on a charging circuit, and a voltage comparator to turn it on at .5 volts or greater and off .3 volts and lesser.


I attempted this and found that at the slow speeds that I prefer to run at will not turn on the light. Also at slow speed the diods tend to get real hot (given an extended period of run time.


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## gunrunnerjohn (Nov 10, 2010)

Why would diodes get hot with low current?


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## tkruger (Jan 18, 2009)

gunrunnerjohn said:


> Why would diodes get hot with low current?


I wish I knew. Maybe I had a bad one or something.


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## gunrunnerjohn (Nov 10, 2010)

I'm just wondering exactly how you have that wired.


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## T-Man (May 16, 2008)

For me constant brightness is achieved by leaving the throttle alone.

I have collected old Peter Thorne books that have circuits for constant lighting. One had to do with higher frequency. The information is almost outdated and parts may not be produced anymore. Current books aren't cheep either.


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## T-Man (May 16, 2008)

The constant brightness for HO is a high frequency AC output , around 7 volts on DC track. That way you get lights when the motor is off. Four books were written by the author. Most of the books have track detection, throttles and sound projects.


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## gunrunnerjohn (Nov 10, 2010)

I'm not familiar with DCC, I run O with TMCC, different animal.

If you have 7 VAC all the time, a diode & resistor should give you the constant brightness.


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