For my current project I have a Arduino wired to 5 externals modules that requires a precise 5V input (CT measurement). The cable between the Arduino and theses modules will be a 4x0.22 mm² of about 1.5 meters long.

My questions are the following :

  • Can I create a clean 5v from a 9v AC to DC transformer inside my Arduino case (regulator + capacitor) and power up the Arduino and all modules from there without having loose in my modules voltages ?

  • Or should I transport 9v to each module and create the 5v current onto each module board ?

  • Also, which type of regulator should I use ? They will be enclosed in a small box, I don't know how much heat 9v to 5v are going to generate.

I only have a bit of electronic experience on bread board, I have never deployed a project in real world situation, so I am bit confused about the best practice to use.

Additional information:

  • I would like a voltage precision of +/- 0.1v
  • My externals modules are also homemade, they are basically composed of a AC relay and a CT. My precision need is for the CT voltage measurement.
  • The only component drawing current in my modules is the relay, so at the maximum 5x 90mA + the arduino consumption (with Ethernet Shield).
  • 3
    \$\begingroup\$ You must be very specific about what you mean by "precise 5V input". Do you really mean accurate? How much variation can you tolerate? This is going to have a big influence on your design choices, so don't say something like "as accurate as possible" or "as inexpensive as possible". \$\endgroup\$ – Elliot Alderson Jun 3 '19 at 12:57
  • \$\begingroup\$ Please add a link to the manufacturer's datasheet for the "module". \$\endgroup\$ – Elliot Alderson Jun 3 '19 at 12:59
  • \$\begingroup\$ How much current does each of your loads require? \$\endgroup\$ – Dave Tweed Jun 3 '19 at 13:07
  • \$\begingroup\$ Welcome to EE.SE! Keep in mind that questions about optimization (i.e., "What is the best ...?") require a definition about what problem dimensions are to be optimized for your application, such as size, speed, energy consumption, user experience, etc. Since these can't be optimized all at once, you need to have a good idea of which ones are most important to you, and be able to articulate that clearly to us. \$\endgroup\$ – Dave Tweed Jun 3 '19 at 13:07
  • \$\begingroup\$ Informations added \$\endgroup\$ – Karnalta Jun 3 '19 at 14:57

If you are powering your modules over a fairly long wire, when the relay actuates there will be an additional voltage drop across the power feed wires. Therefore I suggest you generate the required 5V locally at each module derived from a raw 9V supply derived from the Arduino. A search of Ebay, Banggood or possibly Alibaba should turn up some suitable cheap PSU modules. For example on Bangood there are these.
I assume you have sufficient decoupling at each module that any transient will not affect the sensitive circuits or feed back to the Arduino.

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