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I am on a project to build a 8x8x8 LED cube having common cathodes in each layer. I have built the cube and now I have to build the main circuit. I am using my Arduino Mega 2560 to control it.

I have a big problem in selecting transistors for the layer of the cube. I saw a video in which she used two 2N2222 in parallel to get the desired output. Can anybody help me how is that done.

How can I connect two 2N2222 in parallel to get double the current rating? Or can anybody suggest another MOSFET which can be used in my project.

Please provide the pin diagram so that I can understand clearly because I am working for the first time with transistors and MOSFETs.

Actually I have 64 anodes and 8 cathodes . I am driving 64 anodes using shift registers and i needed the help on 8 cathodes section.

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    \$\begingroup\$ Putting BJTs in parallel is not recommended. Start with an appropriate device in the first place. \$\endgroup\$ – Ignacio Vazquez-Abrams Apr 9 '15 at 4:52
  • \$\begingroup\$ What other you can recommend \$\endgroup\$ – Yash Lotan Apr 9 '15 at 5:04
  • \$\begingroup\$ I recommend finding a parametric selection tool. \$\endgroup\$ – Ignacio Vazquez-Abrams Apr 9 '15 at 5:26
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    \$\begingroup\$ replicating someone else's design is always complicated. you might find the solution if you ask yourself these question: 1)how to drive a single led with arduino?, 2)what does transistor do in the circuit to drive led?, 3)how many leds you want to drive from a single source?, 4)what is current requirement for driving those many leds?, 5)which transistor can provide that current rating?, 6)which biasing mode do you need? we can help you in directing you towards answer. Don't expect that someone should solve this problem for and directly post answer with all schematics. \$\endgroup\$ – Damon Apr 9 '15 at 7:23
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First understand why you are using 2N2222. The output from the Mega 2560 is not enough to drive all the 8 LED's connected to the cathode(As each pin can only offer unto 40mA of current). Thus, you need a transistor to provide enough voltage and current to drive all the LED's connected in that line of the cube. Consider this circuit in which the 2N2222 is being used as a voltage follower:-

2N2222 as a voltage follower

The base will be connected to the Arduino and the Collector will be given the supply which is needed to drive the LED's. Your cathode will be connected to Vout(in series with a suitable resistor).

MOSFET's serve the similar purpose as a transistors but they have their own pro's and cons.

Since you are using a 8X8X8 cube and there will be 64 cathodes. Using 64 transistors is usually not recommended and will make things very difficult for you. I suggest using transistor array IC ULN 2803A or similar IC's.

I would suggest you work on 4X4X4 and learn from the problems you face and then move on to 8X8X8.

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