I am trying to make a circuit that is running up to three loads in parallel, consisting of the Arduino Nano, a heating element (20 ohms), and a stepper motor that can take anywhere from 9-38 volts. I was planning on having the two elements that are going to be taking relatively large amounts of power (the heating element and the motor) at 12 volts while being toggleable by transistors connected/controlled by the Nano. The Nano itself is just processing inputs from buttons and running a simple coreless DC motor that can run anywhere from 1-5 volts and minimal amps, like 15mA at 2 Volts, along with like 3 small LEDs. If I did everything right the diagram in progress should be shown below.
My question was, is a 78L05 voltage regulator circuit connected to the Vin and Gnd pins of the nano sufficient to power the Nano and all it has to do? I know it supports up to 100mA output and the Arduino only supports up to like 256mA input through the Vin or something similar. LM78L 100-mA Fixed Output Linear Regulator datasheet (Rev. L) (ti.com)
Thanks for the drawing! Wish more members would post that, as You did.
Personally I used the 7805, max 1 Amp, in many projects but if 100 mA is good enough, go for it. Checj the data sheet for input voltage versus current draw. That's where heat is created.
That all depends on the current delivered by the 12 volt power supply.
It really looks like that. Sum up the currents needed and You know.
I expect the Nano draws minimal current. The issue would be the "coreless DC motor". What does it draw? The Nano can/should only provide 10 to 20 ma of current. "DC motor" sounds like it will require more.
And BTW your mosfets will not work as drawn. A P-Channel mosfet would need the Nano output to go to at least 11volts to turn it off.
If the 7805 is conducting 100mA after dropping 7V ( 12 - 5 ), it will be dissipating 700mW (0.7 Watts) as waste heat. Will it overheat? Look at fig, 1 on page 9 of the datasheet. If powering the Nano with 5V, connect to the 5V pin, Not VIN, that takes a minimum of 6.5 to 7V.
I just ran a test with a voltage-controlled power supply for both the 12 Volt line and the 5 Volt line (separately connected), and the current draw of the 5 Volt line appears to be 96mA with every component powered up. I know there's typically supposed to be a degree of error requirement; should I switch to the 7805?
Running from a voltage-controlled PSU with all the components turned on, the 5V line drew 96mA; Due to room-for-error, should I switch to the 7805 or similar?
Take a look at a buck regulator, some can be gotten that will plug into the same slot as a TO220 7805 and will give you more current and less heat. I have seen them for under a buck from my favorite china supplier.
Consider buying a few and taking a good look at how they are built. Most are close to the factory data sheet. From this you can get an Idea if it is worth building your own or purchasing.
It's probably heresy, but an alternative would be to place a high-wattage resistor between the 12V supply and the Arduino Vin pin. The value would be whatever reduced the voltage at Vin to about 7V when the Arduino is drawing its maximum power. You would be dissipating just as much heat, but mostly in the resistor. At very low currents, the drop across the resistor would be small, so the Nano's regulator would see most of the drop. But the current is low, so not much heat. As the current increases, more of the drop is seen across the resistor, so even at high current, the regulator won't heat up much.
By the way, in your original drawing, the output of the 7805 would go to the 5V pin, not the Vin pin. Vin would need 7V or more.
I have seen this done and it is dodgy at best. At today's prices that would be a more expensive solution and not very energy efficient then the buck regulator.
