Need to hack blinking LED kit

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NEO-Tech
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Need to hack blinking LED kit

Post by NEO-Tech » Sat Jan 04, 2003 3:49 pm

I have a cheapo blinking LED kit that uses a 555 timer, 4.7 mfd cap, two LEDs, resistors and 9 volt clip.<p>Now I want to blink LED 4 clusters (aftermarket) from my 12 car power source. Each cluster has an absolute max of 60mA. <p>Is the fix simple enough like changing the resistors in the original kit and have the clusters blink as intended in the original kit set up.<p>I'm not very good at this yet. Thanks in advance.<p>
Phill
Phill

russlk
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Re: Need to hack blinking LED kit

Post by russlk » Sat Jan 04, 2003 6:18 pm

The LM555 operates from 12 volts and will sink and source 200 mA, so all you need is current limiting resistors in series with each LED. 270 ohms should work for 4 LEDs. Don't use the CMOS version, it doesn't have the drive capability.

bridgen
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Re: Need to hack blinking LED kit

Post by bridgen » Sun Jan 05, 2003 8:18 am

The way I read your posting is that you want to flash the 4 clusters all at the same time. If that is correct then the total current, of 240mA, will exceed even the bipolar 555 version's capacity and you will need to add a transistor between the 555 and the leds.
If this is the case and you aren't sure how to do this just give the word and I, or someone else, will explain.
Regards.

bridgen
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Re: Need to hack blinking LED kit

Post by bridgen » Sun Jan 05, 2003 12:12 pm

Phill,<p>I've stuck a quick hand-drawn circuit on my web site www.davidbridgen.com. Go to the "Electronics" page and look for your name.
I shall send this to you as email and post it on the forum, so other people can take a look too.<p>Regards,<p>David

Dimbulb
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Re: Need to hack blinking LED kit

Post by Dimbulb » Sun Jan 05, 2003 4:32 pm

Here is a step by step approach.( a little dry)<p>As a separate entity a simple amplifier takes a very small sample from the 555 and makes that signal large enough to drive all kinds of leds.
As you know LEDs can be damaged easily (murphy's law).<p>Concider connecting just one LED first using only a resistor then the rest of them are ditto. If you measure the current by connecting the DMM in series with the resistor then you will know it is safe to connect the LED in series with it observing the polarity for the led. For example the positive to the resistor to the led terminal and the terminal with the flat side goes the the ground.<p>Using a DMM and a resistor and car power source you should be drawing 10 or 20 mA which means the LEDS are 1-4 volts. the resistor then depending on which LED you are planning to use. R=VI example:
13.5/.020 = 675 and I*R=V .030*275=8.25<p>Off the shelf radio shack 276-2030 a 2N3053 ( a medium power NPN transistor )a hearty beast.
Another favorite is the 2N2222A in a metal case.
Small but not soprano.
Need to get back to connecting the workhorse later but first.( putting the dog before the cart) a few simple other details. Easier when you approach this one piece at a time. The merging of these entities is always balance and is what allows you to work nicely with AC signals.

Let me know how it works and how much current you are drawing (18mA) ? What is the voltage across the resistor (1.7V)? Now try this with just an LED,resistor and a the car battery. What is your opinion, bright ! maybe you need super ebay 19,800 ucandelas !<p>Then the 555 needs to connect assuming you want it to run on 12V. Lets drop the current. this can be accomplished the same way (Ohms Law) How many mA is the 555 circuit drawing ? Then 13.8/I = R lets assume 13.8V /.045 Amps = 307 ohms resistor for the main of your oscillator (where the battery connects or power input). Also the other organs are shared with Ground.<p>At this point you have both the led and the 555 running on the car battery. So now you are ready to increase the power to scale-up to the LED cluster size. Recomennd you put a resistor on each LED and connecting them in a parallel fashion then all the leds will light even if one should burn out. As Russ said with the easier method. A nice circuit board is helpful on this portion, that way you can move the light board where you want.<p>The last part to concider is to limit the current through the amplifier by choosing a resistor to put in series from the emitter to the ground. The final connection from the amplifier to the LED main by tapping into the collector + and ground - .
Now that I built this in my head you can find my errors and make it work. If you want to take this one further you can insert a sequential chip that fans out to the lights the using just the 240 mA may be enough probably 40 mA variety driven by a 2N3904 on each to really blast somebody, I have a super bright from radio shack and I set my adjustable power supply at 4 volts.<p>[ January 06, 2003: Message edited by: dim bulb ]</p>

NEO-Tech
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Re: Need to hack blinking LED kit

Post by NEO-Tech » Sun Jan 05, 2003 8:16 pm

Thanks guys, great information for free. I will let you know how I finally get it to work.
Phill

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dacflyer
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Re: Need to hack blinking LED kit

Post by dacflyer » Sun Jan 05, 2003 10:07 pm

i got one even simpler !<p>goto radio shack...get you a blinker led..and series the leds and resister it...and you got it...what could be simpler...uses less power than a 555 also.... :)

bridgen
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Re: Need to hack blinking LED kit

Post by bridgen » Sun Jan 05, 2003 10:56 pm

I don't understand where dim bulb gets the "1 to 4 volts across the resistor" from.<p>A normal red led will have around 1.8 to 2 volts across it when forward biased - more or less constant irrespective of the value of current through it. <p>If it is run from a car battery then there will be around 12 - 2 = 10V across the resistor - up to a couple of volts more if the engine is fired up.

Dimbulb
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Re: Need to hack blinking LED kit

Post by Dimbulb » Mon Jan 06, 2003 5:19 pm

Thanks David I am embarrassed to say I really should have checked my numbers, I will have to revise the post.

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