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I've to have a 2 Ardunio and 1 Netduino in a board, they are connected to +100 component. All I need is less than 5A so I bought a 12v 6A power supply and need to ask some questions so I avoid doing anything stupid.

  1. Is it safe to take a 5V (after passing the 12V to 7805 or some other way to get 5V) and give it to the 2 Arduino and the 1 Netduino?
  2. Is it better to give each component it's own fuse or should I just use fuses for major parts?
  3. I can give each component it's rated voltage and the current will be given to each component as it needs from the power supply knowing that I should not take more than 40mA from the Arduino pins, am I right ?

Sorry but this project is major and I'm more of programmer than electrical engineer :)

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  • \$\begingroup\$ Was there any particular reason why you didn't go with a regulated 5V supply in the first place? \$\endgroup\$ – Ignacio Vazquez-Abrams Feb 18 '15 at 3:54
  • \$\begingroup\$ yeah because i need 12v for some components, 6v for other components, so the power suply is actually 12v 5a and the dc dc converter is 5v 5a, so i would have both options to use \$\endgroup\$ – AndrewxXx Feb 18 '15 at 3:57
  • \$\begingroup\$ @40mA on an output pin you are pushing the device to its absolute maximum rating which is bad design practice. Also total maximum current for the whole package is 200mA. Using these currents, the pin output voltage will differ substantially from 5 or 0V. \$\endgroup\$ – jippie Feb 18 '15 at 6:54
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1) Yes, generally speaking it should be fine to send the 5V to the arduinos and netduino, unless any of them have ADCs or DACs that you intend to use and that are sensitive to voltage source fluctuations. Note that in any case you should include a capacitor at the voltage input pin to each chip. Use wires/traces that are thick enough to transfer the current that you need, and best not to put the chips in series along a single power line (unless the power line is sufficiently large to minimize the voltage drop along it.

2) I've only ever needed to put a single fuse at the input of the entire circuit board. I wouldn't expect any average use-case to need more fuses than that unless you're worried about some IC drawing too much current or feeding the power supply to a daughter board.

3) Correct, as long as you keep the current below what your voltage regulator is rated for. Note that if you are drawing 5A and plan to use the 7805, then you're going to burn (12V - 5V) * (5A) = 35W just in the regulator. You'll need a beefy heat sink. A switching DC-DC converter might be better for this case.

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  • \$\begingroup\$ yes i was planning to use a DC-DC converter of 12v to 5v up to 5a with the power supply output dc 12v 5a then it's compatible right ? also would cat5 wires going to be able to hold that much current ? how thick should my tracks be ? sorry it's just a huge project for me and i really don't want to mess it up :) \$\endgroup\$ – AndrewxXx Feb 18 '15 at 4:17
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    \$\begingroup\$ If you a switching converter, then 5V @ 5A would actually then draw only about 2A from the 12V source (calculated by (5V/12V)*5A), so that is just fine. A general rule of thumb for max current in wires is to not allow more than 500A per cm^2 (cross-sectional area). If the cat5 wire gauge is about 22AWG, then that is 0.0033 cm^2, and should carry no more than 1.6A (per wire). If the cat5 has a long length then it should carry much less to avoid voltage drops. Make sure you pair power and ground on a twisted pair, otherwise you'll have noise induced in the other cat5 wires. \$\endgroup\$ – mith Feb 18 '15 at 4:28

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