External power for Arduino & 5940

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When you want to deliver power to components directly, and not tax the onboard power regulator on the Arduino, here's one way to make an external, regulated source:

Disclaimer: I am not an electrical engineer! As with all the commentary on this site, my suggestions may or may not work in your particular situation. [Always test with some simple version of your circuit first. Use a multimeter to confirm current, voltage, and polarity. Sniff the air and make sure nothing is smoking!] This information is offered without any warranty or guarantee of any kind. Use at your own risk. Now go have fun...

Here is a closeup of the power supply arrangement I used in my first Arduino + 3 TI 5940 circuit seen on this page.

Regulated power supply circuitRegulated power supply circuit

Among the great resources on the web, this site has an excellent description of this circuit.

NOTICE:
1. The maximum current the 7805 regulator can handle may not be enough for your circuit. If you find the regulator getting uncomfortably hot (some heat is normal), you should attach a heat sink to it. You will find heat sinks designed to fit the form factor of the 7805, which is "TO220". There is a digestible article about this chip here.
2. If your circuit draws even more current than the 7805 can handle, you will probably need a different regulator, one that is rated for higher current flows. EXAMPLES: National Semiconductor LM1084 [link to Farnell in the UK], ST Microelectronics LD1084[link to Digikey in Minnesota,USA]. These are spec'd to have "output current up to 5 amps."
Check the pinouts on those regulators! They may not be the same as on the 7805 shown above.

In my opinion, you normally will not need the "adjustable" type, just go for a unit with fixed-voltage; the circuit is simpler.

WHY?
What's the point of having an entirely separate power supply when the Arduino (or any other microcontroller board for that matter) already has its own, similar circuit? Two reasons:

I was uncertain how much current the onboard Arduino power supply could deliver, so being hyperconservative (about circuit design, anyway), I decided to supply the power through my own source. And, I knew that the Ti 5940's would want a very stable voltage, and thus I thought providing power directly would be a better solution than putting demands on the Arduino (which also wants a stable supply for its own logic).

If you think I'm delusional, or at least ill-informed about this, let me know. But so far, for me, nothing is smoking.


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