I am trying to come up with a way to make a circuit for a tail light on my motorcycle. My idea comes from seeing tail lights on a Lexus SUV I just cant figure out how to do it.

What I want is a tail light with three sections. Middle section for use as brake light always then left and right sections to work as a brake light and as blinkers.
I want all three sections to light when I use my brakes but when I turn on the turn signal switch I want the corresponding side of the light to blink as a blinker even when I am applying my brakes or not.

I have an old motorcycle that did not originally come with turn signals and
I do not want to buy some ugly turn signals that bolt to the fender I have 6 volts available for power.

 

I hope your motorcycle is not one of those extremely noisy ones with pipes instead of mufflers that disturb everyone for blocks around and wake everybody all night long???

I live 3 blocks from a major road and can't hear any cars (just the tiny noisy ones with kids driving them) and I hardly hear a truck (some also don't have mufflers). But I hear every motorcycle and the exhaust sounds like a machine gun. Horrible noise!

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Uncle $crooge

 

I know what you mean...I actually do live by a pretty busy road...and at 2 in the morning you can just hear them come roaring by for a while...I really don't see the point of having them that loud.

 

If you do a search on this forum, there must be atleast 50 topics on this subject.

I agree about the loud bikes! Same with the pickups the kids take the mufflers off of cause they think it sounds cool. It really gets me when I am taking a walk with my wife, and a bike or truck goes past and we can't even continue our conversation until it is a quater mile away!

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Wow thanks for hijacking the thread.

If you could show me a post about what I want, I would be glad to read it.
Everything I found was for blinking brake lights not what I want to achieve. That is a very basic circuit. I guess I asked the wrong group.

 

I would assume that the tail light fixture is going to have three bulbs. There will be 4 wires to feed the fixture. 1 common, 1 left turn, 1 brake, and 1 for right turn. Is this right?

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Assuming that the answer to this question is yes, then what you need are 2 Schottky diodes.

You will have to buy diodes that can withstand the current through the filament when it is cold.

So measure the resistance of the filament with an Ohmmeter and calculate the current that will flow initially. The current will reduce as the filament warms up, but you need to be sure that the diodes won't blow on the initial current.

I suggested Schottky diodes as they have less forward voltage drop than Silicon ones.

For example, the 1N5819 is rated at 1 Amp max continuous, but if you look at its data sheet, it will tell you what the allowable max peak current is.

However, I suspect (without looking at the data sheet) that the 1N5819 won't be able to withstand the current, so you will have to look for one that will.

Assuming that your bike has a negative earth, connect the anodes of the diodes to the brake wire and the cathode of one to the left side lamp and the cathode of the other to the right side lamp.

The diodes will prevent the centre brake lamp and right blinker from glowing when you turn on the left blinker, and vice versa if you turn on the right one.

But when you apply the brakes, both diodes will conduct and all three lamps will glow.

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Len

 

Hi Len,

I don't understand how this will let the turn signal blink if the brakes are applied. It seems to me that this configuration should make the brake light turn on all lights, regardless of the state of either turn signal.

I would think you'd need something like an NPN transistor with collector to the diode cathode, base to the turn signal line via a current-limiting resistor, and emitter to the lamp. Maybe a pulldown on the base too. Does this make any sense or. . .

Am I right and if not what am I missing?


Torben

 

I did not think about the need to make the blinkers work while the brakes are on, but obviously, it is necessary.

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Len

 

What the OP needs to buy is one of those adapters for connecting trailer lights to a car. Or he can make his own with a couple of relays:
http://www.designnews.com/contents/i...n%20Signal.pdf
http://www.designnews.com/contents/i...0schematic.pdf
The first design relies on the tow vehicle's existing light bulbs to provide a current path for the relays. The second circuit is a little more complex, but is better suited for the OP's application.

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I could not open the first link posted by kchriste.

The second one only has two lights on the trailer. The Op needs 3.

So here is my suggestion. The relay contacts are connected in the exclusive OR configuration. Thus if a blinker only is required, the respective relay blinks and energises the respective lamp.

If the brakes are applied, all 3 lamps glow.

If the brakes are applied and say the left blinker is selected, the left lamp blinks and the other 2 glow continuously.

Diodes D1 ~3 protect the switches from the back EMF of the relay coils, ie. the diodes clamp the back EMF to about 0.7 Volt.

Virtually any diode can be used, it only has to withstand is the coil current when the switch is opened.

I have assumed that the bike has a negative ground. If it has a + gnd, then reverse the diodes.

Attached Images

Blinker circuit.png (85.9 KB, 49 views)

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Len

 

Torben,
This would only blink the lights if the brakes are applied. Also, if the brakes only were applied, only the centre lamp would glow.

You need exclusive OR gates, ie. the electronic equivalent of the relay version I posted above.

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Len

 

I have now studied the second link posted by kchriste in more detail.

It can be altered to include the brake lamp and has an advantage over the one I posted above as it does not need the battery connection.

So I have attached it re-drawn so that even I can understand it.

I've added diodes to protect the switches as before. Again, reverse the diodes if the bike has a + gnd.

Attached Images

Blinker circuit 2.png (85.1 KB, 30 views)

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Len

 

Why not use a 12F629 PIC and 3 logic level mosfets?
Use 3 of the inputs for your switches, and the remaining 3 for driving the mosfets and the individual bulbs..
Writing the code for the PIC, and sorting a schematic will be a simple task.
If I remember, I'll try and knock something together tonite..

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I actually just found those trailer adapters and was thinking of going that route and moding it to my needs. Does anyone know if those trailer adapters will work on just 6vdc because that is what I have to work with. The ideas you guys have posted are looking like other options I may have to go with and they do look promising for me.