ok, so I found my old arduino and a lcd screen...did a google search and found the datasheet for the lcd screen
now my question is this:
it says voltage should be 3.3v, and current 2.5mA...so by ohms law, I should have a resistor value of 1320?
could I serial connect 1x 1k, 1x 250 and 1x 100 resistors for this ?
(not native english speaker...so maybe serial connect isn`t the right wording...but I hope you understand what I mean)
I am trying to learn how to figure out what parts require which resistors...and all I can find online is references to LED`s and no real info on any other examples..
2.nd question:
I have a computer fan with a sticker that says DC 12v, 0.41A and some odd ~055 number.
would this mean I need a 30watt resistor? 12/0.41 = 29,26
thank you for any help on this topic...and please if you are gonna use examples...do not use Led`s
Forget about the resistors.
Supply the voltage requested. Be prepared to supply the current shown. The device will, at a maximum, use the current shown when you supply the voltage shown.
There is no need for resistors in either case. Connect the LCD, directly, to 3.3V and it will draw the current that it requires. Connect the fan, directly, to 12V and it will draw the current that it requires. The resistance is kind of built in to those parts. LEDs are different in that they will conduct almost like a piece of wire once their forward voltage is exceeded, hence the need for a current limiting resistor.
The best source for this sort of information is usually the data sheet for the part.
LEDs, neon bulbs, and fluorescent light bulbs require a series resistor or other current control and are the most likely things that you are going to encounter that require something additional.
Hakaari:
...
is the idea that if I have a power supply that exceeds the power need, I need to provide resistors? ...
No. The power supply is capable of providing all the current it is rated for, but only WILL provide the current your components (called the 'load') will actually use. Power supplies don't PUSH current, components PULL current.
In an actual project you would want the power supply to be capable of providing 1.5 or 2 times the current the load will draw.
...
so if all I have is 5v and what I want to power is 3v...I would need resistors......but if I have 3v available, it will do everything by itself?
Again no. Well, a tempered no. You could use two resistors as a voltage divider, but that is not recommended because they waste current, and limit the current to the load. You would want to use a voltage regulator to change 5 volts to 3 volts. There are two types of voltage regulators: linear and switching. They both do the same thing, but switching regulators (also known as 'buck' converters) are usually more efficient when used near their rated current. Linear regulators are cheaper, and often easier to hook up, although they may require a heat sink to remove excess heat from the unused voltage.
so it seems to me it is a guessing game if a part requires resistors or not
Nearly all components do not require current-limiting resistors. Most things that do, are light emitters, such as the afore mentioned LEDs, neon bulbs and fluorescent tubes. In each case, the device makes a short circuit when powered up. Both neon bulbs and fluorescent tubes need higher voltages to run, so if you are doing "normal" low-voltage projects with an Arduino, LEDs are the only thing you'll need to worry about. You can calculate the exact resistor to use for a particular current with Ohm's law or just cheat and always use 330 ohms (or there abouts - 180 will be brighter, and 1000 will be dimmer.)
so it seems to me it is a guessing game if a part requires resistors or not
It just takes study, learning about each part and its behaviour - Typically individual devices
have behaviour determined by their physics, so LEDs for instance are current driven, meaning
a resistor is needed if powered from a voltage source.
Circuits people design (including integrated circuits) almost always are made to expect a voltage
power source, as this is most convenient. For instance 12V LED strips have internal resistors so
they can be powered from a constant 12V, many logic IC's expect a 5V supply, etc etc.
Hakaari:
so it seems to me it is a guessing game if a part requires resistors or not
No it's not a guessing game. It's a "learning a bit about electronics" game. Like many other things, including programming, electronics is not something you can do successfully by just guessing what you think should work.
Hakaari:
so, how do I know which parts require resistors and which don`t?
is the idea that if I have a power supply that exceeds the power need, I need to provide resistors?
so if all I have is 5v and what I want to power is 3v...I would need resistors......but if I have 3v available, it will do everything by itself?
Hi,
A friend of mine asked his father what branch (of engineering) to choose: the two basic choices were electrical (electronics included -at the time) or mechanics.
His father (engineer too) told him: "Electrical; mechanics can be learned almost on the fly (by practising), electrical engineering is impossible: you have to study it before doing anything".
Regards