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Topic: Rescue Squad lightbar (Read 1 time) previous topic - next topic

dewyoder18

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

tack

#1
Dec 17, 2012, 02:36 am Last Edit: Dec 17, 2012, 02:47 am by tack Reason: 1
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.

fungus

#2
Dec 17, 2012, 02:44 am Last Edit: Dec 17, 2012, 02:47 am by fungus Reason: 1
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.


No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

dewyoder18

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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?

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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.



dewyoder18

I can't wrap my mind around the NPN transistors!!!  :0

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