I am going to make a 5x5x5 LED cube. i was going to use the colomns of the LEDs for the anode and have the anode of each LED in the colomn connected. Then i was going to connect the cathode of each LED in a layer together and use it to control the cathode of each layer. that way i can turn on a certain layers cathode and a certain colomns anode and get a certain LED to light up. i will be using an arduino uno and as many transistors and shift registers as i need. i also have thought about using MOSFETs, but i think since each LED uses about 20ma, i will only ever have 100ma max going through a transistor at a time. i do believe a transistor can handle that. but my question is what transistors i should use to turn the anode and cathode on and off. i should be able to use some basic transistors due to the small amount of current that will be going through each one. but my main question is what i will do about power. i think im going to buy 2 5Volt 2Amp dc wall wart power supplies. that would be plenty of power to power everything, but the LEDs are only 3volts each. so i am either going to use resistors, or i am going to put some high current voltage regulators between the power supply and the power to the transistors that turn on the LED anodes. i really dont want to have to wire a resistor to each LED, but if that is the best choice, i can do it. any help is appreciated. i do not know much when it comes to this stuff. i am trying to use this to learn and figured the challenge would be nice.
well, i would much rather use the shift registers because of multiple reasons. i see what you are saying, and that makes perfect sense. but i really want to do it with shift registers. i know it will add more parts and wires, but i am willing to do that if i can use shift registers. thanks for the advice, though.
I would suggest that switching speed depends on the selected MOSFET.Th '328P is all CMOS(FET), and it switches 40mA outputs pretty quick.
Choose one with low input capacitance.
I would suggest PNPs for common anode layers, and open drain shift registers, TPIC6B595 type, on the cathode columns.Can use 5 '595s, 25 for cathode, and 5 to pull the PNP gates low to turn them on.Each TPIC6B595 can easily sink the 160mA from 8 LEDs all on at once at 20mA if want them good & bright.
TPIC6B595 are 83 cents at avnet.comWho is asking $2 each?Less likely to make wiring mistakes with fewer parts I would think.
https://avnetexpress.avnet.com/store/em/EMController?langId=-1&storeId=500201&catalogId=500201&action=products&term=tpic6b595&Nn=25&N=100153+429495611278 cents. avnet.com is a US supplier. I ordered a tube of 20 a while ago. Don't recall what shipping was. You have other parts to buy also?If not, 74HC595 and NPN transistors will work too.
What crossroads says is pretty accurate. Basically what he is saying is that using parts that meet or exceed your needs will reduce your chance of premature failure. You could get away with 595s, they wont break right away, but your needs exceeds the parts specifications, and *may* cause premature failure, and its not the proper way of doing things.There are actually a lot of ways to solve this problem. I do like your idea of controlling 5 LEDs at a time, and doing that in a loop of 5 that is inside another loop of 5, and you have controlled all 125 LEDs. I dont think that I have seen that one before. It will have an extremely low duty cycle, so It will probably end up very dim, which is probably why we dont see that technique being used. It also means electrically isolating rows, which maybe tricky to make the structure hold up. its still an interesting idea, and may be worth playing around with.If you limit the current to 8ma to your LEDs with resistors, you could reduce the current to the diodes to 8ma, then you would be within the 70ma max current spec of the 595s, and well within the LEDs specifications. Another option is to simply run the LEDs and shift registers over spec, and expect to replace them sometime i the future, it can take months to wreck your leds or shift registers. You could build a spare in that time, and have it ready if this one fails.
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