same circuit 2 5V supplies

Hi,

Sorry if this has been covered before but I have done some searching and still not satisfied.

I am building a shield for an UNO that will power a single Max7221 chip and an LED clock display. It works but I want to
make sure that I don't draw too much current from the Arduino as I am adding a few other elements to the circuit.

My solution is to add a separate voltage regulator to supply the Max chip and LED display and simultaneously use the Arduino's
5v supply for the switch and the optocoupler. Both grounds would be shared.

Does anyone know whether this is good or common practice ? I can't find many examples as typically people are driving things
from the pins and therefore using transistors etc.

I have attached an image of the circuit. The regulator will go in the 3 pins to the left of the 5v pin.

Many thanks

Simon

Picture 6.png

Oooh look, a cute little blue maze! 8)
johnnefastis, a picture of the traces without a schematic is not very useful. If you attempted to include the schematic, it didn't make it, please try again,

You can have separated 5v supplies for the various components/system pieces, as long as they all share ground as you plan to do. If there are vast timing differences as to the when the 5V is available around the system, that might be an issue.
If the supply feeds the barrel jack on the arduino and the separate 5V regulator, that is an ideal situation.

You can have as many 5V regulators as you like. As long as your grounds are all connected, then 5V is 5V anywhere, however it is generated.

One thing to watch with your circuit though - pretty as it is you should never have right-angles (except for T junctions) in your circuit. You look at any professional designed PCB and you will seldom see a right angle. This is not a cosmetic thing:

  1. During the etching process copper can get trapped in tight corners like right angles, and that can lead to shorts between adjacent tracks.
  2. Sharp corners radiate EMI. The only time you should have sharp corners is for an intentional radiator, like a PCB trace aerial.

Use 45° miters on all your corners.

Thanks CrossRoads and Manjenco,

Thats really useful. Sorry the schematic is a bit of a mess but here it is.

I will go ahead with it with the two supplies, I have even done it before but I just wanted to double check.

I guess the other option would be to cut the voltage regulator from the Arduino and run the 5volts from the
higher current regulator. But then I think I would get into USB power danger. I will stick with it as is.

Thanks for the tip about the rounded edges. I normally cut the boards on a CNC and they
are usually ok but I will definitely keep that in mind from now on.

Thanks for your help.

Cheers

My general rules for multiple power supplies:

  • Always connect grounds (unless 100% isolation is a mandatory requirement, and the circuit was engineered to support that.) Done.
  • If the device will be using the power sources as alternates (like, battery unless plugged in to mains), diode-isolate them so the higher voltage wins, and the lower voltage is blocked.
  • If the device will be powered simultaneously with different supplies (like, 5v logic and high-current supplies), the supplies must be inherently constrained to their intended components. Usually by transistors, or ICs that have high-impedance inputs (no pull-ups). Otherwise, current can flow between the supplies, which is almost never what you want.
  • If the behavior of the circuit is undefined without a specific power-up sequence, ensure this order by using earlier stages to open transistor gates for all later stage's power rails, or by using power sequencing ICs.

I realize your schematic is a work-in-progress, but you should really add descriptive labels to your jumpers, inputs, and really all the other parts too. It's difficult to spot potential errors when you don't know what's on the end of J5. :wink:

If powering the Uno via the 5V header, put a diode from 5V (anode) to Vin (cathode) also to prevent reverse driving the 5V regulator.