How to select a suitable resistor and capacitor value for a circuit?

Can anyone explain for me how to select a suitable resistor and capacitor value for the circuit, and what need to consider doing components value selection.

i had upload a circuit diagram, can anyone explain the operation of the circuit. thanks for your help....

lm35+rs232

As far as these micrcontroller based circuits are concerend, people can judge their operation by looking at them, but still not 100% sure.Because you don't know what kind of Software is being run on the controller itself.The circuit operation depends on the software too.To understand the microcontroller based circuits, you need to know the Hardware+Software.I don't know what software is being run.But as far as hardware is concerened.It's simple.
For the power supply, usually step-down transformer is use, but it can also be a transformer less power supply.Any ways, LM7805 is a +5Volts regulator.It will give you the smooth +5V DC voltage.

You have MAX232 for serial communication with the PC.For serial communication RS232 is used mostly with DB-9 connector.This circuit has the ability to send and recieve data with the PC.

You are using two pins of controller to accept Analog input, that is coming from the LM35(Temperature sensor IC) and voltage divider as the reference.

More over there you have pull-up switch button on OSC1.Other things like Reading rate select,etc can be understood by means of the software, then you can know for which purpose they are to be used.

If you talk about digital circuit and analog circuit, a person can understand them, because they usually contains hardware that don't require software.The schematic then itself reperesent their function.But looking at the micrcontroller schematic and try to predict the 100% operation is not always correct.You have to consult the Software for this too.

Can anyone explain for me how to select a suitable resistor and capacitor value for the circuit[/quote
They are already given on it, but they have small fonts.

Click to expand...

components and their jobs in a circuit

umery2k75, thanks for your reply, here another question: if i want to design my own circuit, so how to determine the suitable resistor and capacitor value or others components value? thanks again

serial communication, smooth, max232

Well in every circuit, components values are pre-calculated and the person knows which values to use.

There are different strategies for which the person installs only specific value components.

If you want to use some ICs like Microcontroller,Voltage Regulator, Temperature Sensors,etc in your circuit.
You will then read it's Datasheet and it contains lots of information.But in Datasheets, there's mostly TYPICAL APPLICATION too.As how you can use the IC.Regardless the specific values of temperature, current requirement, voltages, etc and regardless of graphical representation of device,their behaviour with temperature, their junction temperature,etc there's always given TYPICAL APPLICATION.You don't need to look at all those details, your prime focus would be the typical application.Typical Application circuits already contains resistors,capacitors,inductors,etc values.Their usages are also defined and and it's given what effect they would pose on the circuit operation.But mostly we don't calculate all those resistors,capacitors,etc values.The typical application diagram makes our job easy and mostly we are able to use that particular IC with the typical application design.Making circuit with the components whose job is known is EASY.

Let me define the above point in more details.
Suppose you take Temperature Sensor(LM35), voltage regulator of +5V(7805), for serial communication (MAX232), their job is already defined.As what they are made to do.You'll always get the typical application as how to use them and you can make use of such ICs very easily.Such components jobs are dedicated to only one thing.LM35 tells you temperature, 7805 regulates the voltage, MAX232 does the communication job,etc.
On the other end, there are components, whose jobs isn't that specific or dedicated, like PNP transistor or NPN transistor, JFETs,MOSFETS,GTOs,SCRs,TRIACs,Resistors,Inductors,Capacitors,etc. They can be use in so many application and in so many ways.A BJT transistor can act as a amplifier,switch, inverter, and has different roles depending on the way you use it.For such components you need to calculate resistors,capacitors values, because their application is huge.You need to have knoweldge for what you are doing.So you can do right accordingly.

In your circuit, PB1 is used as a switch.You can google and can find many types of switches that you can make and also values doesn't matter that much in this type.So for pull-up switch like PB1, mostly people use 3.3K or 10K,etc resistor for pull up.We don't care because mostly we people use switches are connected to devices that use TTL levels, in your circuit PIC controller use TTL voltage level.In TTL +5V is 1(binary) and 0V is 0(binary).So if you use 3.3KOhm resistor for pull up you'll get reduce voltage to around 4.5V or something like this, or if you use 10KOhm resistor you'll get voltage around 2.0 something voltage.So these voltages do comes in range that the devices using TTL leves registers them as either 1 or 0.That is 1(binary) is considered in the range if voltage comes in (2.0V to 5.5V) or 0(binary) is considered in the range if voltage comes in (2.0V to 1.8V) range.So if you are using switch like the way PB1 in your circuit is using.Here 10KOhm is used, but you can also use 3.3KOhm,4.7KOhm.They all are correct uptil to the point, they comes in the proper range.

Choosing components values depends where and for which you'r using, in time critical application, suppose you want to use 100Ohm resistor, you just don't use a normal grade resistor.You then need to have the more expensive precision resistor 100Ohm.Suppose you're making a circuit that would be used for military use, you then use the same IC, but with the military standard.Same IC, suppose 555 timer IC would cost you different in different standards.Most widely used standard are commerical standards,industry standard and military standards.The most expensive would be the military version, because they are design to withstand high temperature,noise and etc.

So most matter, where you want to use your components.Dedicated ICs maufacturers gives the typical application, so this way it would save your time.You can use those ICs.
Making your own application with components whose job are not dedicated, you need to have knowledge for what you're doing.When creating circuits, you need to break your circuits in module and you need to know what different modules would do and what their jobs are.If you want to make power supply, you then research as how to make a power supply, you read about voltage regulators, etc.At the end you make your power supply, then suppose you want to make another module, you then research as how it could be done.At least you need to know what the module does.Like Amplify the signal, Isolate the signal,etc.

For good start.I would recommend you to have the copy of Encylopedia of circuits.It contains thousands of small modules.Circuits with different functions and uses.Suppose you want to make the circuit that is realted with TV.You can then find so many TV based circuits and you then choose which one you like.Complete working detail is given on them.So remember, for making a good circuit, atleast you need to name them properly, what module would do.If your module works as a Radio Frequency reciever, you can find the circuits related to Radio Frequency reciever.So many circuit.You then see which one best suits you.May be you don't use all those Radio Frequency reciever, you just analyze all those and take all good points from all Radio Frequency circuits and make your own circuit.Nobody starts from the scratch.Like you can't make a Intel Pentium 4 Processor(complex circuit) starting from the single resistor.No one can make it.No body! In electronics bottom down approach is use.Means first you decide what your application will do, then you go little depeer, you break your application in block diagram(means you identifiy big components of your circuit[Example of Big components of your car=4 wheels,1 engine,pertol tank), then you break your circuit in modules, then you research about modules, then you make individual modules alones, then you test their working properly, then you interconnect different modules together.In the end you have a complete circuit.If some one just looks at the final circuit which you have just made, containing all those compoents.He would just say, it's damn complex!! I can't imagine to make myself one.Things do look complex if you don't use correct strategy.While making circuits, you design one thing, then another ,then another thing.In the end, you might have a very big and complex circuit containing thousands of components which will be working perfectly.