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Topic: 8x8x8 multiplexed LED cube with an Arduino Mega 2560 (Read 41 times) previous topic - next topic

Un4Seen

Thank you, CrossRoads!

So, in other words we do need the 220 Ohm resistors between the shift register and the NDP6020P-ND gate. We also need pullup resistors between the gate and source of the NDP6020-ND and their value should be 5 KOhm.

As for the LED current limiting resistor, I understand now which components drop voltage and need to be taken into account. I guess your guess of 0.5 is from the NDP6020-ND. I've read the datasheet, not just once, but I can't figure out the voltage drop based on the graphs. Here is the excat datasheet of the NDP6020-NDs that I've bought from Farnell: http://www.farnell.com/datasheets/59594.pdf

The 3.3 voltage drop for the LEDs is a correct assumption.

One more important question: CrossRoads, in your image the Arduino had some additional things (capacitors, resistors) connected to some pins on the top and left, so it would seem that not only the MOSI, SCK, SS and GND pins are connected. Is that needed, or is that just some leftover from another circuit? If needed, what values would those be and what is their role?

Thank you very very much or your answer!


CrossRoads

Ok, I didn't realize the NDP6020 was a MOSFET with 0.023 ohm on-resistance. Its voltage drop will be 0.023 * planned current (# of LEDs per row) or very small.

I drew up a standalone microcontroller circuit; if you are using an actual arduino, those are already built in, so you only to connect to the SPI pins and Gnd.
The standalone circuit has 10K reset pullup resistor, 16 MHz xtal, 22pF caps, and 100nF caps on VCC/AVCC/Aref.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Un4Seen

Thank you, CrossRoads, very much! :)

So that means that the voltage for which we need to calculate the current limiting resistors for the LEDs looks like this:

5V (source) - 3.3V (LED) - 0.08V (TCIP6B595) - 0.023 * 64 * 0.02 = 5 - 3.3 - 0.08 - 0.03 = 1.59. In other words we need 82 Ohm resistors. Luckily I have a few hundred of those laying around :)

At this point  I understand the driving circuit 100%. I will soon post an updated diagram to reflect the reality accurately.

In the meantime I'm progressing with the 4x4x4 test cube. You guys were right when you advised me not to start with the 8x8x8 one. No amount of theory can prepare you for the difficulties encountered during soldering. A practice cube is a must. In a few days it will be ready and I'll come back with pictures.

Thank you all for your help!

CrossRoads

1.59V/20mA = 79.5 ohm, 82 being a standard value should work well.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Un4Seen

Here's the updated, hopefully 100% correct circuit diagram:

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