Brand new to electricity & hobby electronics here, and I just watched this video on calculating the resistor needed for an LED, and I had a basic question about that process that I (surprisingly) could not find an answer to.
In that video, the setup is very simple:
- 9V battery
- LED rated at 9V and 20mA
Hence the author explains that you need a resistor rated at:
R = (V2 - V1) / I = 9V - 3V / 20mA = 6V / 20mA = 300 ohms
Math is simple, and makes sense. Well, mostly...
However the battery is outputting/supplying (giving off?) 9V of voltage. And a cursory Google search yielded that the avergae 9V battery outputs/supplies (gives off) ~5mA of current. So to me, in my newbie/dummy brain:
- The battery is providing us with 9V @ 5mA
- The LED requires 3V @ 20mA
- This means we need to lower the voltage by 6V (9V - 6V = 3V); and
- It also means we need to raise the current by 15mA (5mA + 15mA = 20mA)
My assertion: So by lowering the supplied voltage from 9V -> 3V and by raising the supplied current from 5mA -> 20mA, we are providing the LED with the correct voltage and current that it needs to operate successfully & safely.
So to me, the problem here is:
How do we "convert" the outputted/supplied voltage & current to the required voltage & current of the component (in our case, an LED; but could be anything I guess, a buzzer, a motor, etc.)?
So my question here is: am I correct in asserting that the way you decide how to wire any component to a voltage source (9V battery in this case) is by deciding on the required adjustments to both voltage and current? Or do we just care about voltage? And why?! (For example, are there some cases where we care about making supplied voltage equal to required voltage, other cases where we only care about making supplied current equal to required current, and maybe other cases where we care about both?)
So if you really read between the lines of my question, I'm looking for the strategy on determining what "supporting components" (resistors, transistors, capacitors, etc.) need to be added to make a voltage source "compatible" with some other IO component (LED, pushbutton, buzzer, motor, etc.).