# COMMUNITY : FORUMS : TECH

## For electronic n00bs

This topic is made to help all who don't know a lot (or even anything) about electronics. Here people can ask simple questons without opening a new topic.

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BC-456 years ago
OK you guys i need help with AND , OR , AN and Not gates what are there functions and how do they work in electronics need help on that
Chicken22099 years ago
can someone explain something to me I don't exactly see the resistor's purpose as a nonmoving switch point me out where I go wrong here Lets say you have a basic circuit with a lightbulb as a load On that circuit you have a transistor, hooked up to another circuit with a switch so when its pressed, the circuit works. What's the point of that transistor, why not place the switch on the main circuit
9 years ago
Presumably you meant "transistor." The point is that the load (light bulb) current can be controlled by a MUCH smaller signal than the load requires, AND it's electronic. So instead of physically making two pieces of metal touch to turn on your desk lamp, a microcontroller can do it by outputing a small signal (0.1W or less; 5V@20mA) on one of it's pins, even if the load is a 20W bulb (12V @ 2A) (or more.) (And it's fast too. Switch that 20W bulb on and off 100 times a second and you can control the brightness by varying the ration of ON time to OFF time.)
9 years ago
as wave maker transistor can be connected to other components that return 'echoes' of current to it. the transistor amplifies the echoes and sends them to the circuit. then gets new ones . . . in this way transistor can be used to make a constant stream of pulses or wave this is used in many circuits. for example flash circuit in a camera. the transistor converts DC (constant current) to AC (wave). then the AC can be amplified with a transformer to the high voltage required to fire the flash. there are some 'ibles here on how to use the flash circuit for various stuff another option is to set up 2 transistors together so they switch on and off each other in a rush. the effect is the same - stream of pulses that can be used for various stuff. such circuit is called multivibrator as part of digital devices transistors can be connected together to make more complex stuff in the circuit you have connect a second transistor in parallel with the 1st one. connect C and E of both transistors together. connect B (the base - the control current) to some other switch now if ANY of the switches is close the led is on now connect the new transistor in series - disconnect E of the 1st transistor from - and connect the new one in between now if any of the switches is open the led is off now leave only the 1st transistor and disconect its base (B) from the switch. instead - connect it to the + thru a resistor. the led should be on all the time now. take the second transistor. connect C to the B of the 1st one. E to -. B to the switch. now if the switch is close the led is off (you kinda inverted the way the switch works) the circuits you made are called AND OR NOT gates and are the 3 basic blocks of which any digital circuit (like programmable controller and computer) is built.
9 years ago
A transistor or other silicon switch is used when the source of the switching is a logic (or analog) signal. I.E., when it's being switched by an IC, transistor, or other device, there isn't a mechanical switch being used at all.

Practically, transistor switches are way faster than any mechanical switch or relay, anyhoo.
9 years ago
yeah, but to make the transistor act as a switch, it itself needs a switch to turn it on and of
9 years ago
Nope, bipolar transistors are essentially current-amplifiers.

In WestFW's diagram, the amount of current flowing through the load resistance (r1) is Ic, and is proportional to the base current (Ib). If there's no current applied to the base, then there's no Ic current, either....

So another device, say a microcontroller or even a 555 chip, will supply the logic signal to the base. No mechanical switch is needed.
9 years ago
can you dumb it down a bit?
9 years ago
A regular mechanical switch actually physically disconnects the two sides of the circuit (it makes or breaks the connection.)

But a transistor acts more like a valve. It blocks the current (rather than disconnecting it) when there's no current applied to the base (the "input" of a transistor.) It's easy for some other electronic device to supply (or deny) that base current.
Dantex (author) 9 years ago
here's bunch of questions 1. witch is the main difference i work of NPN and PNP transistors 2. can you recommend me some all purpose diodes "for simple projects, no more then 9 v) 3. witch is the difference between linear and logarithmicall potentiometers
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