there is a 5v pin on the arduino between the GND and 3.3v pins, are you saying that I should connect the 5v pin on the max7219 to that pin? in that case , I would just need to supply all of my power through the arduino, correct? and am I also correct in assuming that I could use the power jack to provide 8v 1 amp of power to the arduino and it should all work? I am unaware of how many amps the 5v pin on the arduino can handle.
Here's the thing. The Arduino has a on-board voltage regulator whose input is connected to the power jack. It requires 7-12V as input, and reduces it to the 5V required by the board itself. The output of the regulator is connected to the 5V pin on the Arduino. (And the input from the power jack is connected to the Vin pin.)
BUT in doing its thing, the regulator dissipates (wastes) as heat the difference between 5V and the input voltage connected to the power jack. How hot it gets depends on (a) how large the voltage difference is, and (b) how much current is being drawn. The amount of power in watts that the regulator needs to dissipate is this voltage difference times the current. The regulator is small and does not have a large heat sink area. Trying to draw an amp through it with a differential of 3V means it will need to dissipate 3W, and that is going to make it very
hot. It will likely shut itself down (most regulators have self-protection circuitry), or worst case it could be destroyed.
I thought you had a single 5V wall wart. In which case, as long as it is decently regulated, it can be fed in
to the 5V pin, and the power jack left unconnected. And it can also power the 7219s (and hence the LEDs) simultaneously.
OTOH if you have two supplies, one which is 5V and one which is 8V, you could plug the 8V into the Arduino's power jack, and connect the 5v supply to the 7219s, just be sure to connect the grounds between the two. Earlier comment on bypassing still applies. This will require minimal current (~50mA) from the 8V supply, and the 5V supply will provide all the current for the LEDs.
Hope this helps.
OK, and if I split a 1 amp supply parrallely to two circuits, they won't each get .5 amps? because if the current just divides itself equally, I will provide too much current to the arduino. I would need .5 amps to the arduino and about 1 amp to the LEDs. On an unrelated note, I used to live in Goodrich, just south of Grand blanc! small world haha!
No, as CrossRoads said, each circuit will draw its required current. Current and voltage are not independent quantities
, they are proportional to each other. The constant of proportionality is called resistance.
Goodrich! That makes you a Martian! Always loved that. When did you move away?