I am completely new to electronics and bought a starter kit a couple of days ago, and it's so much fun! I'm a bit confused by one thing though and was hoping that you guys could share a bit of your knowledge with me.
An example book was included in the kit, and one of the first things it mentions is Ohm's Law, which isn't problematic itself. However it's never referred to again afterwards.
The examples explain how they are created when introducing new components, but they never explain why they chose to use resistors with a certain component, or the choice of 'strength' of the resistor. I understand that they've calculated it using Ohm's law, but since I don't know the specs of the components I'll just have to trust the schematics, which is a bit disappointing.
Now I get that a LED needs a resistor or else it may brake. And if I don't add a resistor to a simple switch button, I will create a short circuit.
But how do I know when a component is 'strong' enough to do without a resistor? Do you read the datasheet of each component to figure it out?
Can you try to explain your process in a few steps when creating new circuits?
There are so many different functions that resistors perform in all the various possible electronic circuits that trying to detail all of them would amount to a complete electronics course.
There are pullup and pulldown resistors in switch circuits and the value of these is not very important, anything in a wide range will work. In many cases for a new design the value is chosen "because that's what is normally used".
The value of resistors used to control the current in an LED circuit is important as described above.
Resistor values in filter and oscillator circuits and other timing circuits are critical to getting the correct timing or oscillation or filter frequency.
And so it goes on. For any specific example you run across you might get an explanation but covering the whole scene is for an electronics textbook not a forum post...sorry.
Also, when working with components in Arduino projects, you see the same values of resistor appearing for the same component or usage:
Transistor base resistor 1K
LED 330R
arduino pin, or transistor base pullup/pulldown 10K
arduino pin protection 1k
Of course, these are quidelines and there can be valid reasons for having other values.
Then other applications have their own values, depending on the requirements:
timing circuits (as already mentioned)
level changers (say 5v to 3.3v) - here you'll need ohms law to get the correct values.
etc.
Now I get that a LED needs a resistor or else it may brake. And if I don't add a resistor to a simple switch button, I will create a short circuit.
But how do I know when a component is 'strong' enough to do without a resistor? Do you read the datasheet of each component to figure it out?
The answer to part of your question is YES you must read the datasheet for each component. After some experience you will know which datasheets are important.
You will also learn that 90% of the design decisions are a compromise. i.e. there is seldom a "perfect" answer.
But lets look at the switch example.
Its not obvious but switches have two "resistance" values:
Open = very high ohms, typically considered as infinite ohms.
Closed = very low ohms, typically considered 0 ohms.
Lets assume your voltage supply is 5 Volts.
If you put a switch across the supply the current would be:
Switch is open, Current (I) = E / R = 5 /infinity = essentially Zero current. OK fine this is not a problem
Switch is closed, Current (I) = E/R = 5 /0 = infinite current i.e. a short circuit. This will damage your voltage supply.
Hmm... so what can we do to lower the current in the switch closed situation?? Lets try adding a resistor in series with the switch we'll try 1 ohm.
Switch closed case: Current(I) = E/R = 5 / (1+0)) = 5 amps. Better but still too high.
We'll try 10 ohms ---> 5/(10+0) = 0.5 amps better but still way too high
We'll skip a few decades and try 10,000 ohms ---> 5/(10,000 +0) = 0.0005 or 0.5 milliamps. This is a good number so we'll use that.
LED's require a similar approach but are more complex because the current in a diode does not vary directly with voltage it is non linear. You can google how to calculate a LED resistor.