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My plans are to hook up everything as the picture shows... I used Fritzing to create this PCB. If there is something you see that isn't hooked up right please tell me... I am not familiar with the NPN transistors but from what I could find online I think I have them hooked up right. I am planning on testing everything using a breadboard before I start soldering everthing! This will be my first prototype that I've put together!

Thanks


* Led light bar_pcb.jpg (197.65 KB, 3531x1176 - viewed 48 times.)
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I don't see any current limiting resistors in the Base traces to the transistors. I also don't see any capacitors on the regulator input/output or decoupling capacitors on the MCU voltage pins.

It also looks to me like your LED's are simply connected across 12v and Gnd, so will always be lit.

It appears that the transistors will be driven by the ATTiny but they are just going to apply a short between 12v and Gnd when switched on.

I'm assuming the intention is that the ATTiny is supposed to control switching of the Left/Right direction LED's via those two transistors?

As it stands you'll have some nice bright LED's on but you'll also fry your ATTiny and transistors and have some magic blue smoke.

You might want to look at it all again.
« Last Edit: December 16, 2012, 08:47:35 pm by tack » Logged

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There's dozens of things wrong with that circuit...for a start the transistors seem to short out your battery. They'll die as soon as you turn them on.


« Last Edit: December 16, 2012, 08:47:51 pm by fungus » Logged

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Quote
I don't see any current limiting resistors in the Base traces to the transistors.

Thanks I completely forgot about those! Will a 1k resistor be enough?

Quote
I also don't see any capacitors on the regulator input/output or decoupling capacitors on the MCU voltage pins.

I wasn't sure if I needed capacitors on the regulator due to the fact that the ATtiny84  I am going to use to flash the LED's in different sequences can handle voltages from 4.5v - 5.5v If I still need these let me know...I am new to this type of stuff! Thanks

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for a start the transistors seem to short out your battery
How do I hook up the NPN Transistors? I have the 9v+ flowing into the collector the -(negative) hooked to the emitter and the ATtiny84 switch hooked to the Base.


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I can't wrap my mind around the NPN transistors!!!  smiley-mad
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Use the datasheets for the components you're using. They will show typical arrangements.

At the moment your transistors are connected across your 12v supply and Gnd. The ATTiny digital Lin will apply 5v directly to the Base and the Transistor will simy short the power supply out!

Your LED's should be in the Collector side of the transistor and you should have an appropriate Base resistor so that enough current flows to saturate the transistor and turn it on as a switch. The value will depend on the DC Current Gain and the Collector-Emitter Current required for your LED's. That brings another issue once you have a correct circuit. You say the LED current is 75mA. If driving those via a single transistor then it needs to be rated for 75mA x the number of banks. A typical 2N3904 type NPN will switch 200mA so you need to specify appropriate transistors for your load. 6 banks would be 450mA.
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for a start the transistors seem to short out your battery
How do I hook up the NPN Transistors? I have the 9v+ flowing into the collector the -(negative) hooked to the emitter and the ATtiny84 switch hooked to the Base.

No you don't, you have the 12V line connected to the collector and the emitter connected to ground. The electrons passing the LEDs don't go through the transistors.

Your '75mA' calculations are off, too. You have twice as many LED strings on one side as on the other so the current on one side should be double the other (and I don't think either side can really be 75mA, not with the stated LED voltages...)

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http://www.kpsec.freeuk.com/trancirc.htm

Access the above link and scroll down to 'Connecting a transistor to the output of an IC'
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I can't wrap my mind around the NPN transistors!!!  smiley-mad

Last time you posted about this project I suggested a simple solution that wouldn't need any pesky transistors or resistors ... the current regulation and switching was all done for you by AN6884 chips.

(or use KA2284 which are exactly the same...)

« Last Edit: December 17, 2012, 06:42:00 am by fungus » Logged

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   This may be a bit closer?


* traffic.bmp (385.06 KB, 2040x1540 - viewed 28 times.)
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Ok, so you have 20 sets of 3 led's, you say they are 3.5v and 75ma?  So you would need something like 1.5amps to run it.

If you dropped it to 15-20mA per strand you could run that led circuit on a 555 timer....
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Ok, so you have 20 sets of 3 led's, you say they are 3.5v and 75ma?  So you would need something like 1.5amps to run it.

No, a string of LEDs is 20mA.

20x20 = 400mA.

If you dropped it to 15-20mA per strand you could run that led circuit on a 555 timer....

Or, I dunno ... use some 50 cent devices that have five constant-current inputs each (ie. can drive five strings of LEDs), need no external components and can be switched on/off in huge banks with a single Arduino pin. Even with PWM...

These, for example:

http://www.ebay.com/sch/i.html?_nkw=AN6884

Or these (which are exactly the same but different manufacturer):

http://www.ebay.com/sch/i.html?_nkw=ka2284+driver

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Sorry fungus, the 75mA i was referring to was from the OP's questions, I think he wants to use High Current Led's.  When I refer to 20mA im talking 20mA at 12V.  Using an led series calculator set at 3.5v per led and 20ma, with a source of 12v + a little from the resistor.  
http://led.linear1.org/led.wiz

His lights will also only be half on at a time, from what I understand.
So one side on other side off and then they would switch.

That's why I was referring to the 555 timer, some can sink and source 200mA.  And 555's are 50cent devices, and 2 pots and 2 caps are pretty cheap.... But from what I can tell from Multisim it would fail and die.

http://www.instructables.com/id/41-LED-Flasher-Circuit-using-555-IC/   << something like what I was thinking w/out the transistors.
« Last Edit: December 19, 2012, 03:10:26 pm by Donziboy2 » Logged

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