# Resistors and what needs them

I have been looking and looking for anything that would point me in the direction but can't find anything

All I want is a list of what components use resistors not just LED's, do buttons or motors need etc need them.

Also clear instruction on how to decode datasheets so I can work out what resistor to use with a component. Because as far as I can tell there are only 2 numbers needed per datasheet and there is a lot of info on them

Way to vague a question.

Lots and lots of uses for resistors.

It would take a great deal of time to list them all.

Resistors are not used by components, a resistor is a component. They are widely used and in schematics and drawings should be called out in the BOM (Bill Of Materials). We don't decode a data sheet, we read it with an understanding of the terminology used. The problem I see is trying to learn to swim in the deep end of the pool. You start with the basics and fundamentals and work from there. You learn what the basic components do and how to apply them in design.

Ron

Maybe it would help to say that there are a LOT of different resistor values available. But here is the thing to know. You don't need EVERY value if you stick to 5V related digital electronics. You can actually get by with a small assortment in your bin.

1. 220 Ohm - For things like LED's.
2. 330 Ohm - Same reason as above
3. 1K - For things like BJT transistors
4. 4.7K - For Pullup resistors
5. 10K - Same reason as above

As a bare minimum... if you have at least these in your kit... you can get by.

In digital electronics the most common use is as a "pull-up resistor" (and for LED current limiting).

The [u]Digital Read Serial Example[/u] uses a pull*-down* resistor which is the same concept. (The Arduino actually has optional built-in pull-up resistors that can be enabled.)

With the Arduino, unconnected inputs are "floating" and they might read high or low. If you connect the pushbutton without the resistor the input is floating until you press the button which forces the input high. So, the resistor "pulls down" the input pin to read low when the button is not pushed. When you push the button and make a direct-connection to +5V, you "overpower" the pull down resistor and it reads high. And when you push the button, current flows through the resistor depending on the voltage & resistance (Ohm's Law).

With logic circuits, "open collector" (transistor) and "open drain" (MOSFET) outputs are common, and these require a pull-up resistor.

In linear/analog circuits resistors can set the gain of an amplifier, or to bias a transistor or MOSFET to make it operate in it's linear range.

[u]Voltage dividers[/u] are common in analog circuits, and they are sometimes used on digital inputs (such as for converting a 12V "signal" from a car to 5V for the Arduino.) Potentiometers and/or volume controls are variable voltage dividers.

P.S.
I've been working on a little analog circuit that's got 3 resistors (and other components) - There is a "pull-down" resistor on the input, a "current limiting" resistor on the output, and a resistor that controls the [u]discharge time[/u] of a capacitor.

gillbilliee:
I have been looking and looking for anything that would point me in the direction but can't find anything

All I want is a list of what components use resistors not just LED's, do buttons or motors need etc need them.

Easier to list those that don't. Typical CMOS logic families don't need resistors as everything is HIGH or LOW.
Motors and other power electronics avoid using resistors where high power is involved, since that would
waste power.

Also clear instruction on how to decode datasheets so I can work out what resistor to use with a component. Because as far as I can tell there are only 2 numbers needed per datasheet and there is a lot of info on them

OK lets look at the simplest component, a resistor. What may need to be on the datasheet?

Resistance value
Tolerance
Temperature coefficient
Range of temperature it is designed to operate over
maximum power rating
maximum voltage rating
frequency response (for RF use)
physical dimensions of the case
soldering instructions (temperature/time profile)
fusible or not?
resistance material
environmental limitation (max humidity, max altitude for voltage rating)

And probably some I can't recall just now off the top of my head.

As you can see its a bit more complicated than you were imagining.

When we go to a transistor, then there are many more parameters than a resistor.

Resistors are everywhere in analog circuitry, you need to understand the basics of electronics well to
understand what each resistor is doing alas, it can be complicated as I said.

gillbilliee:
I have been looking and looking for anything that would point me in the direction but can't find anything

All I want is a list of what components use resistors not just LED's, do buttons or motors need etc need them.

Also clear instruction on how to decode datasheets so I can work out what resistor to use with a component. Because as far as I can tell there are only 2 numbers needed per datasheet and there is a lot of info on them

I got a lot of different components which can be used for different types of projects.
Resistors - I got over 100 different types.
Capacitor - At least 40 different types.
Inductors - 12 different types.
and I can go on. There are different types of transistors, diodes, ICs (like the NE555, SN74-serie).

So which components you need depend on what you are suppose to use them for. If you have a specific project you need to buy the components required for that project.

All I want is a list of what components use resistors not just LED's, do buttons or motors need etc need them.

It's not clear what your though is to make you ask this question. But perhaps to put your question in perspective ....

It's like asking what machines require oil.

A resistor is usually considered a "support" component, much like "oil" is to a motor. So the typical approach is to say.... "I have a button and I want it to do "_____" what do I need.

Also know that like the oil example there could be hydraulic oil, lubrication oil...etc; there are different resistors.