LED Cube 8x8x8

Step 10 Power supply considerations

This step is easy to overlook, as LEDs themselves don't draw that much current. But remember that this circuit will draw 64 times the mA of your LEDs if they are all on. In addition to that, the AVR and the latch ICs also draws current.

To calculate the current draw of your LEDs, connect a led to a 5V power supply with the resistor you intend to use, and measure the current in mA. Multiply this number by 64, and you have the power requirements for the cube itself. Add to that 15-20 mA for the AVR and a couple of mA for each latch IC.

Our first attempt at a power supply was to use a step-down voltage regulator, LM7805, with a 12V wall wart. At over 500mA and 12V input, this chip became extremely hot, and wasn't able to supply the desired current.

We later removed this chip, and soldered a wire from the input to the output pin where the chip used to be.

We now use a regulated computer power supply to get a stable high current 5V supply.

Comments

[aj1234]

Can anyone confirm if this power supply will work,
http://www.amazon.com/dp/B00509MOSC/ref=asc_df_B00509MOSC1877744?smid=A1XKPQQA6BPGCN&tag=nextagusmp0357683-20&linkCode=asn&creative=395105&creativeASIN=B00509MOSC

Thank in advance.

[jwestenberg]

It is only 1.5A , to be absolutely sure I would go for one that is rated 2.0A or more.
I used a 5v psp adaptor, which actually outputs 5.4V but that's okay because the atmega I am using is rated for a maximum of 5.6 Volts.
Good luck!

[aj1234]

Thanks for the Prompt response! I am going to buy the one you suggested.

[bl729]

So I know that the power supply is supposed to connect to the GND and Vcc power terminal on the controller, but my old laptop power supply only has a round connector where it was supposed to connect to my laptop. How do I get a GND and a Vcc from the power supply that only has a round connector?

Thanks,
bl

[jwestenberg]

If you stick a wire inside the round connector you will get vcc most of the times. If this is the case you will get ground of the metal outside of the connector.
I do advice you to check the voltage with a multimeter, because sometimes the voltage is much higher than it should be. The voltage would decrease when you put more load on it.

If you would want to use it as a permanent power supply you could just cut of the connector and use the two wires, or you could consider putting a female power plug on your pcb.

Good luck!

[lscarmic]

Has anyone tried running the Vcc and ground over the 16 conductor ribbon cable to the latch board instead of powering each board separately? I don't see why it wouldn't but maybe i'm missing something obvious.

Thanks.

Lee

[triumphtotty]

It should work fine. The ribbon cable is usually 7 strand 28awg, so should handle 2A no problem.  The Vcc line is doing all the hard work remember, as the GND return from the cube LEDs goes via the 8-way connector to the NPN transistors.  If in doubt, double-up the Vcc (i.e. use 2 pins).  You could easily relocate the two status LEDs onto the micro board for this purpose.

[Kevmatic]

I put the button connectors on the CPU board and used the leftover connectors for power. 3 power and 1 ground, I think. Or was it 2 each? I can't remember...

Anyway, it worked fine. No visible dimming even at all lights lit.

[razamatraz]

even pinched back to 6 ma per LED this could potentially mean 0.3 amps draw since that board is firing up to 64 LEDs at a time plus latch draw. If you want to put it through ribbon cable make sure to use at least a couple of conductors. 30 gauge can't take much current. I've seen similar done using CAT6 and they use 4 wires for VCC and 4 for ground.

[alahamm]

So if alll 512 LEDs are lit at one time, would we NEED a 5v/10 A power supply?
What if we use a pass transistor with the 7805?

[triumphtotty]

Not at all. You need to read the entire Instructable in detail. The duty cycle for the LEDs is only 1/8 (actually a little less than that due to the delay of programming the latches between layers), so the maximum power required including the microprocessor and board components is around 1.5A with all LEDs on. Using a 2A PSU would be plenty.

[tcrenshaw4bama]

I imagine that the iPad wall charger would be perfect for this situation because it delivers 5v at 2.1amps but I could be wrong

[cinaglia]

I'm confused, is there a reason why you'd want to light up all 64 leds at once? Couldn't you make use of the Persistence of Vision technique to fool the brain into thinking they're all lit up at once?

[louige99]

it does use the PoV effect except it cycles through each layer. you could cycle through each led individually or even a smaller sets except it would require further programming and im pretty sure extra controller hardware as well. its very well built and designed this way and allows for different sized cubes to be made with the same/similar circuitry

[arditvelia]

would this work?

http://www.primelec.com/ite-5v-1a-power-supply-pc-accessories-power-supplies-p5285586?___store=default

[B.F.L.M]

could you use a capacitor or transformer to increase energy effefficiency? If not, is there a way to acomplish this goal?

[ITman496]

I'm not sure if you could. Led's will draw what they draw, you can't reduce that. And in reality, its pretty efficient, since 0.5 of an amp at 5 volts is only 2.5 watts. Which is able to be powered by a standard usb port. So it is pretty efficient.

[ragnarroeck]

LM2575 from national Semiconductor would be a quite easy solution, if you are already working with a 7805, as it is a so called switching power supply, and just needs a couple more of the surrounding parts, but not a lot. The very first schematic on the datasheet http://www.national.com/profile/snip.cgi/openDS=LM2575 shows exactly the circuit to build. 7 to 40V in, 5V out with 1A. For the inductor use e.g. PISR-331M-04 from Fastron. This will only need a tiny heatsink, if any.