Arduino circuit with different voltages

I have a semi-small project, where I need to toggle:

  • 3x 12v 4.8W LED Strip
  • Multiple 5v LEDs
  • 4x 3.3v RGB LEDs

I have all the circuits working separately (LED strip using MOSFETs), but I wondered how to combine them given the varying voltages.

As the project is divided into 3 seperate 'panels' controlled from the same arduino, I thought about creating a small board with 3 4-pin power connectors (for example molex) with pins for (+12v, +5v, +3.3v and GND).

I am very much still learning electronics, so I wondered how I can achieve this?

A few characteristics:

  • 0-1 of the 12v LEDs will be on at any given point.
  • The other LEDs will be very varied in regards to usage.
  • I have a 12v 3A power supply which I hope to use

Do I just solder on some power resistors to the power board 5v and 3.3v pins, or can you point me in the right direction? As mentioned, I am no expert, but I am more than willing to read and learn if I just get a hint as to what pieces I'm missing.

Have you considered using a few SMPS to get the voltages

You have two general options for getting lower voltages from higher ones.

Either you use a linear LDO regulator (you can get from digikey et al). Be sure to check the specs and be sure you know and have appropriate input and output caps - the datasheet will say what kind(s) of capacitors, and what values, are appropriate. This is simple and cheap - but all it does is drop voltage and turn it into heat - so if you're pulling 100mA at 5v from a 12v supply through a regulator, the regulator is dissipating 0.7 watts, and will get warm. The 7805 is a primative example of a linear regulator - it has a fairly high dropout (~2v), ie, it's not LDO - though it would be perfectly effective for generating 5v from 12v. You still sometimes find them in electronics (I always pull them when i do, because it makes me feel better that the best thing we could score at the dump was just take-apart fodder).

OR

You use a switching DC-DC converter. You can get these from ebay for very cheap, but not cheaper than one regulator and 2 caps. These are more efficient, but often have a higher quintescent current.

The choice is usually determined by the current the board will draw - the higher the current, the less appropriate a linear regulator is

#LarryD:: That is definitely also an option. Come to think of it, there will be a PC PSU close by. I could use that, but as far as I remember, only the +5V is on when the PC is off, not the 12v, which I also need. Also, since I might switch to a Raspberry Pi, there will be no PC.

So short version: Yes, a different power supply is definitely also an option.

Since this is a one-off project, component costs are not that important (within reason of course). If a SMPS is the best solution, that is what I'll choose.

#DrAzzy:
Quiescent current is of course a disadvantage, especially considering the system will be 'idle' most of the time. I expect it to be in use for a few minutes a week. I could solve that by powering everything down when it is not is use, including the arduino itself. Efficiency is less of an issue given the infrequent use of the system.

So given that I can shut everything completely off and cost of components are not an issue, what would be the best option here?

Thanks for taking your time to answer this, btw. It has already helped tremendously.

chucara:
Come to think of it, there will be a PC PSU close by. I could use that, but as far as I remember, only the +5V is on when the PC is off, not the 12v, which I also need. Also, since I might switch to a Raspberry Pi, there will be no PC.

It's only the standby +5 V that's on when the computer is off. If the PSU isn't in a computer you can always fire it up by shorting the PS_ON# line (green wire) to ground and connecting a 10 Ω power resistor across the main 5 V output. Remember though that the current limit is very high and a mistake could be costly!

Russell.

Right. I think I'll rule out the PC PSU. I'm thinking that the simplest solution would be to take the 12V power supply I already have and simply add another cheap 5V cellphone charger to give me the 5V without having to worry too much about heat dissipation.

I can then use normal resistors to get to 3.3V or get different LEDs that can handle 5V if needed.