Hi
I'm very new to electronics in general but I have a hard time finding a specific enough explanation to what the differences are besides their capability to handle more or less volts/current and needing more or less volts to switch them on and off.
My project aims to control a flashing sign of leds where each letter will be controlled by a pin on an arduino. As each letter will contain a lot of leds I need to use an external power-source and the arduino to switch on/off the leds.
In the attached fritzing the leds are representative of a long line of leds in series/parallel. There can be lines of leds up to the number of output pins on the type of arduino used in each project.
Right now I'm breadboarding with the transistors that come with the starter-kit: (BC547B). But as I will be putting upwards of a hundred smd leds on each arduino-pin I need something that can handle a couple of amps or more, just to be on the safe side. All while being switchable by the arduino.
I tried finding some mosfets on digikey and came up with this result.
I then tried reichelt.com (where I probably will be shopping) and came up with this list but I have no idea what the difference are between the various mosfets and transistors and their naming conventions (anybody with a good transistor-tutorial please leave a link 
)
My question: What should be where the NPN transistors are in the fritzing-model? How do I go about this in the best way?
I will be using mostly smd-components for the rest of the board, is that viable for the transistors as well or are through-hole better? Will there be need of heatsinks at this voltage/amp-level?
Have a nice weekend.
Kind regards
Jesper
the newbie black smoke releaser.
AOI510, AOI508 from Digikey.
I have 32 of them on this board to drive LED strings as you describe.
http://www.crossroadsfencing.com/BobuinoRev17/
Hi,
Welcome to the forum.
Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png, becasue what your two pictures show are not the same circuit, the Fritzy image has polarities swapped in most components.
Please label emitter, base, collector, E,B,C.
So can you reverse engineer YOUR protobaord circuit and post it please.
Please Do NOT send a Fitzy image.
OPs images.
Thanks. Tom... 
LEDs can be wired in series or in parallel. Each strip requires a current limiting resistor, so that LEDs in series are more economic (1 resistor, low current), but require a higher supply voltage (2V per red LED). Of course multiple strips can be connected in parallel, with their currents summing up on the switching transistor. It's up to you to find the best layout and LED supply voltage for your project.
@CrossRoads
That is exactly what I'm looking for - I will try to replicate this in the near future otherwise I will be back with more questions ;). Probably with regards to programming, right now I need to use one output on the arduino for each string, not quite sure how you do it using only four channels?
@TomGeorge
I did read it and did not see a ban on fritzing images? That was what was easiest for me to use as a beginner. The only thing I see different in the two images are the polarities on the rails are reversed?
@DrDiettrich
As the leds on each letter can be of different colour I will be very aware of different resistors for each string.
Thank you all for the replies so far. I will experiment a bit and get back to you.
Kind regards
Jesper
Hi,
Before you go any further, you asked for this?
https://learn.sparkfun.com/tutorials/transistors
It will help your understanding of BJTs.
Can you draw a circuit diagram of this please?
Is your arduino a pro mini?
Thanks.. Tom...
Hi tom, thanks for the link.
I'm not much at my computer this week, but I'll try and make the diagram next week.
Yes, that is indeed a pro mini, I like the size
Regards
Jesper
Hi again
What's a good (free) program to do circuit diagrams in? Can't seem to find any good/easy (for beginners) ones 
Thanks again.
Jesper
I like www.expresspcb.com for circuit capture for discussions here in the forum. (but not for board design).
Here's a small example.
Hi,
CrossRoads:
I like www.expresspcb.com for circuit capture for discussions here in the forum. (but not for board design).
Likewise, simple, quick, not overloaded with setup and component parameters.
Tom.....
Thanks for the link. I can't seem to find any of the symbols you used in your example (leds, resistors, mosfets etc.). And I can't find them as addons on the homepage - what am I missing here? Do I need to draw all of it myself?
Kind regards
Jesper
@CrossRoads
I tried finding AOI510/AOI508 alternatives on www.reichelt.com as shipping from digi-key is $25 to Denmark. But I can't seem to find any (AO-)mosfets with a low Vgs.
What am I looking for in the name or how to I navigate the different categories (AO, IRF, IRL etc)?
Thanks in advance for your help.
IRL indicates Logic level mosfets, that's just what works with Arduino outputs.
Thanks DrDiettrich
So either of these two should work with an arduino and a bunch of LEDs?
From this listing: reichelt elektronik - online electronics and components specialist
Kind regards
Jesper
