# Maestro Of Circuits

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بسم الله الرحمن الرحيم

A- Do you know resistors?

B= Who don’t!

A- Can you calculate it’s value?

B= I can manage my self. Some times I calculate it through colors, or using ohmmeter.

A- What do you think about resistors?

B= It is way too simple that I really don’t care about it. I am concerning my self most with other component ICs the most.

A- Then, you know micro controller?

B= Yes, that’s why resistors -that can’t be programmed- don’t have any effect on my circuit. I always put any resistor value and it works.

A- Do yo…….

B= BTW, What is this all for? I am already fed up of you.

A- Sorry for that. I just wanna know from what direction do you look at resistors. Can I ask you another question?

B= Last one?

A- All right. Do you know Voltage divider, Pull up-down resistor?

B= Hmm, I heard those names before but can you make it clearer?

A- You can look at these schematics:

BTW, do you know that each component you ever used has an internal resistance?

B= I heard about that before either but as I told you I am not concerning my self with resistors. It can’t affect my circuit.

A- Sorry, but you are wrong. Internal resistance -in my opinion- is the factor that decides the quality of a circuit. You can have two designs for a circuit to do a specific task, but there are always the best choice. To put in your mind all the factors that can affect your circuit, and choose the right component that can make a real big difference. Despite, many circuits can not be working just because of a RESISTOR.

B= I have never thought that resistance can cause a any harm to my circuit. Is there any application that resistor is the main factor?

A- Look, it is not like that always, but it is all concerning about POWER.

B= Power! P=VI=I2R=V2/R.

A- Yes, that is it. Power losses is the worst thing for any circuit. Resistance means you have a power losses that you don’t benefit from. Then you have to choose your right value then you will get the minimum power dissipation. That is what you can call a good design. Also there are some other subjects that have effect on a circuit like high frequencies, and Matching.

B= I didn’t hear about that before!!

A- Resistance -as I think- is the most important thing in electronics. It is too simple to put in mind but has a very big effect. You can call it the maestro of circuits. If you respect it you will have a good circuit design, and if not it will ruin your circuit for no reason. I will talk about things that I did not clear it for you:

How to buy a resistor? Value, sort, and Power

Internal resistance, and high frequency: There are no component -to my knowledge- has zero internal resistance. That resistance may increase in high frequencies, so you have to calculate it right. For example, transistor has an equivalent model the funny thing that there is two resistors in it. For high frequencies there are capacitors added to the model. Capacitors has a resistance that’s why it explodes. Batteries has it too, …….etc. Another thing is the heat, why any component gets hot? It is because internal resistance.

Matching: Some times you have two stages in a circuit one has a low output impedance and the other has a high input impedance. For maximum power transfer you have to match both. There are many methods to do so. Search for it.

That’s why RESISTORS are the maestro. You have to respect it.

Q: In your opinion; What is more important to learn first ELECTRONICS or MICRO-CONTROLLER PROGRAMMING?