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knight rider led modifications????


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Hi, I'm kinda new at this but very enthusiastic about learning so please be patient..
I have built a knight rider led flashing light. Instead of the led's I have hooked up 12 volt relays to run 12 volt lights of course. Will the type of relays that mount on a circuit board carry 12 volt? Is there any way to modify the speed of this flasher by a variable resistor of some sort? And how would I make it so I could get power from my parking lights ( 12 volt ) without burning up the IC? I have tried it as it is and the ic gets very hot... Would just a resistor limit the flow of power from 12 to 6 or 9 volt?
Thanks , Jamie

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New,
Which circuit did you build?
Is it the one in our Projects Section, titled "Knightrider Lights for Model Cars", that uses a 4017 counter chip?
If you connected relays without using anti-spike diodes across them, then you probably blew that chip. Besides, the 4017 doesn't have enough current from its outputs to directly drive relays. It can drive transistors that have a series resistor to their bases, and the transistors drive the relays that have diodes across them.

If you can tell us the spacifications of your 12V relays and the current rating of your lights then we can determine whether your relay is suitable, and we can select a suitable transistor for you.

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As audioguru has suggested, you should post the specs for the 12V relays. Also, what are you using for a power source?
Right off, I do not see diodes across the relay coils to protect the chip against spiking when the relay activates. It is also not a good idea to connect a chip directly to the base of a transistor.

MP

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New,
Your circuit is not a Knightrider, it is a simple chaser. The lights in a Knightrider go back and forth, counting forward and then reverse.
This circuit is designed for an electronic relay that doesn't have a coil. The coil in a relay produces a high voltage spike that destroys ICs and transistors. The spike is arrested with a diode across the relay coil. Your relay coils probably didn't have diodes.
The electronic relays have a small activation current that the small 2N3904 transistors are able to drive. Your big relays require a high current to drive their coils. I am surprised that the transistors didn't melt.
So your 4017 and transistors may be damaged. A good 4017 runs cold when driving a load within its ratings.
Why use a relay to drive a small 4W light? A small power transistor, TIP29, can do it if wired differently, with the light as its collector load, its emitter is grounded and a base resistor from the 4017.

The speed of the flashing can be changed easily.

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New,
We are glad to help you.
Perhaps you didn't understand the difference between your "chaser" that flashes the lights always in 1 direction, and a "knightrider" that flashes the lights back and forth. I am afraid that the chaser may cause traffic confusion since it will appear like a turn-signal. I recommend adding a few diodes to the chaser to convert it into a knightrider, like in our project.

The TIP29 can drive a 12V, 4W light bulb without the 2N3904 transistor.

Increase the flashing speed by reducing the value of the 10uF capacitor at the 555, 4.7uF will make it twice as fast. Instead you could decrease the value of the 22K resistor.

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That sounds easy enough.. ( Feeling Confident ! ) . Now what would the difference be between a tip 29 and a tip 31? I ask becouse Radio shack only has the tip 31, will that work? Also what about the power input? Is there an easy way to change the 12volt input to 9 volt? A resistor of some sort maybe?

Thank you..

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New,
The CD4017BCP has an absolute maximum supply voltage of 20V. To protect it from alternator spikes, put a 100 ohm resistor in series with its supply terminal and a 470uF capacitor from its supply terminal to ground.
That's right, the 560 ohm resistor is in series with the TIP31's base.
Diodes are not necessary unless you need them as gates to reverse the sequence, as in our project "Knightrider Lights for Model Cars" here:

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I hope this is right!! I don't know why this is not showing up right. I made this in paint maybe someone could download it and read it that way. But then again you guys seem to know so much you can probably tell just the way it is. Thank you so much. I never knew getting so frustrated could be this much fun!

post-2440-1427914163613_thumb.gif

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New,
It looks good, except:
1) A wire is missing between pin3 of the 555 to pin 14 of the 4017.
2) A 470uF capacitor is missing from VDD to ground.
3) The 5 ohm variable resistor should be about 50K ohms.
4) If you put the 560 ohm resistors at the transistors, then you need only 6 instead of 10.

For different flash patterns, you need a switch that will completely disconnect this circuit from the transistors and switch-in the other circuit. I have never seen a switch with that many poles (6).

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