# Help with the operation of circuit

Hello everyone,

I’m a beginner to the awesome world of Arduino, and I’ve decided to build an 8x8x8 LED Cube (Yeah, people like me are still trying to make those ;)) I understand how the basic circuit works. However, I’d really appreciate the help of you Gurus to help me understand how the transistor arrangement works in the attached circuit diagram. I could just follow thee circuit and build one; however, I’d like to learn how it works. Hopefully, someone can help me out.

Thanks

Got the circuit from 8x8x8 LED Cube PyroElectro Schematic | PyroElectro - News, Projects & Tutorials

Just like to say as a beginner a 4x4 cube is quite hard .

This might help :

https://learn.sparkfun.com/tutorials/transistors/applications-i-switches

I would say that circuit is not sufficient for driving an 8x8x8 cube.
A cube has 64 LEDs per layer or 8 rows of 8 LEDs, and 8 layers.
They are driven by multiplexing. The most straightforward way, with brightest outcome, is to drive all 64 LEDs in one layer, enable the layer for a short time (30 Hz refresh rate with 8 layers means each layer turned on for 1/8 of 1/30 second = 4166microseconds), then turn if off and repeat for the next layer.
An alternate way is row of 8 LEDs in a layer, then the next 8, then the next 8, etc. Each group is on for 1/8 of 4166uS, or 520uS, and end result will be noticeably dimmer.

I think the best way is to use 8 TPIC6C595 or TPIC6B595 shift registers to sink current for 64 columns of LEDs, with a P-channel MOSFET to source current to each layer. Can use a 9th '595 to sink current from the P-MOSFET gates to determine which layer is on.
Use SPI.transfer() to quickly send the data out to the shift register.

MrsCrossRoads and I are building a 9x9x9 cube, having a center should make for better rotations visually. I made a control board with high current output shift registers (cd74ac164) to drive each column and N-channel MOSFETs (AOI514) to sink current from each layer. She had already started the cube, taking advantage of the longer anode leg for the columns, so I made the control board to match. We’re up to 9x9x7 layers so far.

http://www.jameco.com/shop/StoreCatalogDrillDownView?langId=-1&storeId=10001&catalogId=10001&freeText=led%20cube&search_type=jamecoall

I find the LEDs also light up the bottom of the LED above it - I'd have painted the bottoms of each flat black had I known that. Or used LEDs that diffuse their light more. After you assemble each layer, or column, check that all LEDs work before connecting to the larger structure. LEDs can be bad, or can be damaged during assembly.

hammy: Just like to say as a beginner a 4x4 cube is quite hard .

This might help :

https://learn.sparkfun.com/tutorials/transistors/applications-i-switches

After looking at the link, My understanding of the circuit I posted is this: When the control signal to the base is 0, there is +5V at the cathode of the LEDs, and the LEDs won't turn on. When the control signal is 5V, the transistor is a closed switch, and there's no +5V to the cathode of the LEDs, and they can turn on if the Anode has 5V.

That's all there is to it?

CrossRoads: I would say that circuit is not sufficient for driving an 8x8x8 cube.

I decided to go with this circuit because a lot of people claim that they've successfully built the cube as per that schematic. One guy even said that he removed the Mosfets he used because the 2n2222 transistor pairs worked well.

Do you recommend I should go with different transistors?