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Need sum help wid alot of computer engineering stuff plz....

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umer007

New Member
Can sumone tell me wat a transformer, transistor and fixed capacitor do.

I no abt transformer that it changes the level of voltage and only works with AC. I have this assignment from computer engineering that has fixed capacitors, PNP transistors and a transformer rite next to a speaker. My teacher says the speaker works on AC but i m usin batteries givin me DC. Can sumone tell me wat all these parts do and wt changes the DC to AC so the speaker works. Thx in advance plz reply ASAP.
 

Russlk

New Member
A capacitor blocks DC current and has an impedance to AC called capacitive reactance. A transistor is a current operated device, the current flowing from base to emitter is multiplied by the current gain of the transistor and flows thru the collector- emitter junctions. It sound like you have an audio amp, can you post the schematic?
 

umer007

New Member
i have the schematic on a pc of paper. How can i post it on this forum???wat program do i use to draw it on....paint??
 

Sebi

Active Member
Yes, You should use Paint. Download from this forum some sematic.gif files with many symbols, and just copy/paste to another file.Fast and easy.
 

umer007

New Member
i am tryin to attach the schematic from paint but everytime i clik on attachment an error cum up. Wt shud i do? and if i cant put the schematic here can sumone plz leave their email so i can send it to them or if they have msn messenger plz gimme ur address so i can add u and get sum help personally. Thx in advance
 

umer007

New Member
in the schematic the current ic DC and there is a speaker in it which runs on AC. CAn sumone tell me wt converts teh DC to AC, is it the transformer, PNP transistor or Fixed capacitors. Plz reply ASAP
 

kinjalgp

Active Member
An inverter circuit converts DC to AC. It is nothing but a sine wave or square wave generator. These are the 2 basic waves used in inverters and square wave oscilator is the simplest you can build. And that is using astable multivibrator.
Refer this page for more details on astable multivibrator.
https://www.techlib.com/electronics/flipflopflash.htm
 

najeeb

New Member
Re: Need sum help wid alot of computer engineering stuff plz

umer007 said:
Can sumone tell me wat a transformer, transistor and fixed capacitor do.

I no abt transformer that it changes the level of voltage and only works with AC. I have this assignment from computer engineering that has fixed capacitors, PNP transistors and a transformer rite next to a speaker. My teacher says the speaker works on AC but i m usin batteries givin me DC. Can sumone tell me wat all these parts do and wt changes the DC to AC so the speaker works. Thx in advance plz reply ASAP.

A speaker is similar to a DC motor. have you ever applied AC power a DC motor? You can feel the vibration of motor (not rotation). On the other hand, if we apply DC it will rotate and the speed can be varried by varrying the DC voltage.
By the same way a speaker will NOT work with pure AC but with a varrying DC voltage. This variable DC we feel like AC, since the voltage and hence current going up and down.As the voltage level increasing, sound out put (compare with speed of motor) increases.

But how we will produce the variable power to drive the speaker? for this purpose we need power amplifer circuit. This is you are seeing PNP transistors(Or NPN) with a transformer near the speaker. Here, one transitor amplifies half cycle of a sgnal while the other one amplifies next cycle. This circuit defenitly needs DC power (from batteries) and it will be transformed to the speaker inaccordance with the input signal
 

Russlk

New Member
Najeeb is wrong, the speaker works with AC, not so well with varying DC. The speaker responds to DC, it produces an offset which reduces the available peak amplitude and increases distortion.
 

Chippie

Member
applying a dc source to the speaker coil will just cause the cone to deflect one way or the other..( a good way of determining the positive terminal when phasing.......) if the power source is strong enough you can burn out the coil!!
 

najeeb

New Member
Russlk said:
Najeeb is wrong, the speaker works with AC, not so well with varying DC. The speaker responds to DC, it produces an offset which reduces the available peak amplitude and increases distortion.

I thank Russlk for bringing out this mistake. Actually i wrote this from the information which i got from my school many years back. Today i checked it and realized what i quoted is WRONG.

Also the use of a coupling capacitor will block DC and by pass AC only to the speaker. I didin't think this fact while writing my reply. So sory guys..
 
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