budidharma
New Member
Alright, so lets try and go from easiest questions to most difficult (thought I know their all beginner level).
The first, salving equipment: I found an old PCB yesterday, without hundreds of resistors, capacitors, and ICs. I started removing the resistors and capacitors by applying a soldering iron to one leg, then pulling on that leg with a pair of needlenose pliars till it came out of the solder and hole. Then I did the same to the other side. Is this a good technique? Is there a better way? I assume most of these components will work. I have not been removing the ICs or transistors, though. I assume that they would not be as versitile or easily identifiable as caps and resistors. Am I wrong, should I try to salvage those as well?
Second Question: Say I have a big pile of transistors. I don't know if they are NPN or PNP, and I have no idea how much voltage or current can be applied to them without destroying them. How would I go about testing them, to find whether they are NPN or PNP, and what they are made for?
Third question: I don't really understand Alternating Current. It travels in a sine wave, from 0 voltage to + peak voltage to 0 voltage to - peak voltage and back to 0 voltage. How can it have negative voltage during the second part of that sine wave? Wouldn't this mean that the source voltage has reversed directions and is pushing current the reverse direction through the circuit? The current does have to follow voltage, right? On this, I am very confused. It's covered in TAB electronics Guide in chapter 3, but I still dont' really understand.
I know that changing the amount of current in a wire causes changes in the electromagnetic force around that wire. Does it exert this force on itself? I've seen the term self-impedence mentioned a few times, but not clearly explained. It seems that if the voltage was constantly changing in a condutor with an AC, it would constantly be changing its own impedence as well, what affect does this cause? Can someone explain this to me more clearly?
Third question: Capacitors store voltage. When connected to a DC circuit through a battery and a resistor, a capacitor will continue allowing current to run through the circuit until it has reached its maximum charge and then current will stop flowing. If you then disconnected the capacitor and connected it to a separate circuit using a resistor and an LED, it would power the LED until it's charge had run out. That'd be the basic of a CAP, however, when you apply them to an AC circuit, I don't understand how they work. They are used for filtering, I've read. I don't really understand what this means, or how they work. Can anyone clarify this?
Fourth Question: I can use transistors as switches in a DC circuit. In that sort of environment, I understand how they work. Apply a voltage across the base-emittor and it will allow a larger current to flow across the collector emittor. Again, when applied to an AC circuit, I don't understand.
Alright, all these questions spawn from a diagram I've encountered in the sixth chapter of my TAB Electronics book. It's for an amplification circuit (if you have the book) found on page 163.
Unfortunetly I can't post the schematic (I don't know how I'd get it from my book to this page, I don't have a scanner) and I can't find any similiar ones with google. Like I said it's a simple amplification circuit, you probably all know what those look like.
Thanks!
The first, salving equipment: I found an old PCB yesterday, without hundreds of resistors, capacitors, and ICs. I started removing the resistors and capacitors by applying a soldering iron to one leg, then pulling on that leg with a pair of needlenose pliars till it came out of the solder and hole. Then I did the same to the other side. Is this a good technique? Is there a better way? I assume most of these components will work. I have not been removing the ICs or transistors, though. I assume that they would not be as versitile or easily identifiable as caps and resistors. Am I wrong, should I try to salvage those as well?
Second Question: Say I have a big pile of transistors. I don't know if they are NPN or PNP, and I have no idea how much voltage or current can be applied to them without destroying them. How would I go about testing them, to find whether they are NPN or PNP, and what they are made for?
Third question: I don't really understand Alternating Current. It travels in a sine wave, from 0 voltage to + peak voltage to 0 voltage to - peak voltage and back to 0 voltage. How can it have negative voltage during the second part of that sine wave? Wouldn't this mean that the source voltage has reversed directions and is pushing current the reverse direction through the circuit? The current does have to follow voltage, right? On this, I am very confused. It's covered in TAB electronics Guide in chapter 3, but I still dont' really understand.
I know that changing the amount of current in a wire causes changes in the electromagnetic force around that wire. Does it exert this force on itself? I've seen the term self-impedence mentioned a few times, but not clearly explained. It seems that if the voltage was constantly changing in a condutor with an AC, it would constantly be changing its own impedence as well, what affect does this cause? Can someone explain this to me more clearly?
Third question: Capacitors store voltage. When connected to a DC circuit through a battery and a resistor, a capacitor will continue allowing current to run through the circuit until it has reached its maximum charge and then current will stop flowing. If you then disconnected the capacitor and connected it to a separate circuit using a resistor and an LED, it would power the LED until it's charge had run out. That'd be the basic of a CAP, however, when you apply them to an AC circuit, I don't understand how they work. They are used for filtering, I've read. I don't really understand what this means, or how they work. Can anyone clarify this?
Fourth Question: I can use transistors as switches in a DC circuit. In that sort of environment, I understand how they work. Apply a voltage across the base-emittor and it will allow a larger current to flow across the collector emittor. Again, when applied to an AC circuit, I don't understand.
Alright, all these questions spawn from a diagram I've encountered in the sixth chapter of my TAB Electronics book. It's for an amplification circuit (if you have the book) found on page 163.
Unfortunetly I can't post the schematic (I don't know how I'd get it from my book to this page, I don't have a scanner) and I can't find any similiar ones with google. Like I said it's a simple amplification circuit, you probably all know what those look like.
Thanks!