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Posts posted by f4cepl4nt

  1. How would I go about analyzing a circuit such as the one below? I have a few questions to start with:

    1) Do you consider the antenna an AC voltage source?
    2) What is the purpose of C2? I'm assuming it's to reduce noise, but how exactly does it accomplish this?
    3) If I wanted to use an NPN transistor instead of a PNP, would I just have to switch the diode and battery orientations? Along with capacitors if they are polar.
    4) What is the ground symbol at the bottom of L1 connected to? Is it like the other half of the hertz antenna, or just connected to some big piece of metal, or what?

    One note: The capacitor on the schematic is a variable cap with a rating of 365 MMF, whatever that means. If someone could fill me in on what that means that would be cool too, because I got the schematic from a very old book

  2. Just a quick question or two.... does the sine wave output of a hartley oscillator (or colpitts or another sinusoidal output oscillator) create AC (does the output voltage go negative)? Or is it just DC with voltage moving smoothly up and down?

    Also, if I were to take a 1MHz signal from a square wave generator, (a 555 timer or another oscillator that just makes a pulsed DC output) , and transmit that with an EM wave;  if I had a series LC filter on the receiving end would that properly pass a square wave(or at least pass a sinusoidal component of that square wave)?

    Thanks again...had a hard time finding info on these two questions. My guess would be that the LC filter would pass the sinusoidal component of the DC pulsed wave...and the hartley/colpitts/watever oscillator makes pulsed DC. Please inform me if these guesses are correct! =)

  3. Yeah there were a few sites in there that were kinda useful...though nothing that really explained how antennas work going WAY down to the basics. I'm still confused about how an antenna creates a current out of an EM wave hitting it...or does it? See I'm a little boggled about how antennas affect a circuit. To me, they just look like a piece of wire going nowhere, so how do they affect a circuit at all?

    I'll try to find a VERY basic circuit for a radio receiver, or if anyone can just throw one together and post it here that would be nice, and just give me a run down of how it works, focusing mainly on how an antenna affects the circuit.

    Again, nothing fancy, just the complete basics.

  4. Electronics Resources? We have a section like that? Link me please =)

    I just found an article section and didn't find much there on radio electronics. :)

    [EDIT] oh stupid me he was referring to the forums. Hey, good idea ante, thanks. Will definitely check that out.

  5. Hey again guys, in need of a bit of help again.

    In my robotics class at school (which basically turned out to be a electronics/ infrastructure physics class) we have a summative project due at the beginning of june, and I've got a great idea for the project (mine is a new security feature for a car).

    The only problem is, my solution relies on radio electronics to work at its best, and I'm completely clueless in that field

  6. I need to build a coil with these specs: 1 inch length, .5 inch diameter, ferrite core, 30 turns of 22awg wire and 3 layers.

    Can anyone give me a pretty accurate measure of the inductance of that coil? This is for a capacitor charging circuit, and I've done a few calculations of my own but I figured I'd come to you guys for a little help to make sure I've got it right. I ended up with a value of 32.99mH, (.03299H) but that seems FAR too big to be accurate.

    Anyone with a more accurate calculation please fill me in  :)

    Thanks again guys.

  7. Just a quick question: Lets say I have two transformers, one with a 2:1 voltage ratio and one with a 3:1 voltage ratio. If I were to hook these up so that the voltage gets increased twice, would the output voltage be 6 times as much as the input? Would the current follow the same pattern as well, being decreased by a factor of 6? Please answer these questions assuming no power loss...or give me an idea of how to estimate power loss in a transformer  :)

    Basically I'm just wondering if it would work properly.  ;D

  8. Hahahah its ok Audio, you've helped me enough over time that it compensates for that minor error

    thanks again ;D

    Oh yeah just one more thing: The output of the rectifier will still be pulsating rather than constant voltage, will that affect the charging of the capacitor? Is there any way to change that pulsating signal (From 0-~690V) to a constant voltage?

    Last question! Promise!  ;D

  9. Hey guys, just doing some research into converting voltages, and I was just thinking: Would it be possible to say hook up a 9v battery to a IC555 timer, and connect the output of that timer to the primary winding of a transformer and connect the secondary winding to a high voltage capacitor?

    Just a thought...I've seen so many complicated charge circuits which I couldn't possibly hope to understand  :o ;D

    Just let me know if my idea is completely idiotic or not. Hahahah


  10. Hey again everyone, just one simple question about transistors:

    Why do people say something like 'a transistor typically has .6V from its gate to its emitter and .2V from its collector to its emitter'?? Doesn't the voltage get determined by the rest of the circuit?

    Like for instance, if I put a 10K resistor connected to a transistors collector then saturate it, would there still be .2V between the collector/emitter? How about 100K? Or how about 1G? The way I'm understanding it, no matter how absurd your resistor value for that circuit, there will always be .2V from collector to emitter. (And the same goes for the base-emitter voltage, always .6V??)

    Thanks for helping me with this one, I probably have a few other transistor questions lingering in my mind but I'll look for those later

  11. Ok one last thing: I have a picture of a circuit here, and there is an opamp used, but there is no negative feedback to lower the output voltage


    Lets say the voltage across the resistor in the phototransistor branch is 1V and the voltage across the phototransistor is 11V when there is no light. That means that at the positive input on the opamp there is 11V right? The negative input on the opamp will always be 1.5V in this circuit. So then there is a 9.5V differential to be amplified. On the 358N opamp there is a gain of 100dB (which is 100, 000 times, just like audio said earlier) resulting in a 950 000V output. That can't be right, but there is no negative feedback to lower the output voltage down. Am I missing something? Or would that MOSFET just be blown to smithereens hahah :D

    That is my last question, I promise. Audioguru, you seem a wee bit mad at me, so I'm sorry if I'm asking stupid questions....but at least I'm being decent about it. It's not like I'm saying " Hey Guy5, wh3re ArE teh L33t 5chematICs U arE goin6 to snD [email protected]?!!?11one!?"  ;D

  12. Thanks for the help audio, but aren't bels arranged in a logarithmic scale? So wouldn't 60dB (6Bel) be a gain of 1 000 000 (10 to the power of 6)?

    You said that most opamps have a gain of around 100dB, resulting in a voltage gain of 100 000. Does that really mean the output of an opamp with it's inputs at 5V and 4V (1V total) will be 100 000V? Seem's a little bit big to me, but what do I know  ;D

    One last question, if I were to apply a huge voltage like that (100 000V) to the gate of a MOSFET, would it destroy it? Or would it just be turned on like usual and run fine? Basically my question is, is there an upper limit to the amount of voltage you can apply to a MOSFET?

    Thanks again, a lot of the stuff I read about I don't fully understand until one of you guys give me a down to earth explanation of it  :)

  13. Ok, if the data sheet for a differential op amp says 100dB, then that means a power gain of 10 000 000 000 right? Holy SMOKES! That can't be right. The way I figure that huge number is 100dB = 10B right? And the way to get the ratio gain from B is to put 10 to the power of the bels, so 10 to the power of 10B = 10 000 000 000. Ok so here's my first question: How do you convert the power gain to voltage gain? Because that's what I'm really interested in here (I don't know why the data sheet would tell me the power gain and not the voltage gain

  14. Got it from this awesome tutorial...But I think I solved my problem while you guys were rambling on about misplaced posts  ::)  hahahahah

    I misread the symbol H as meaning henries, where it is actually the symbol for magnetic field intensity, just like L is to inductance. Magnetic field intensity is measured in amp-turns per metre, which makes sense judging from that formula. The first one I noted in my first post was correct though, the one which took into account permeability and area and all that

    The second formula should be like this : H = amperes x turns / meters

    Thanks for the help though guys, without this forum I'd be lost in electronics hahah

  15. I have a question about inductors. Inductance is the same thing as Field Intensity right? They are both measured in Henries. So then why does one formula for figuring out the field intensity rely on the current put through the coil and one doesn't??

    Heres one formula : L = ((Number of Turns)

  16. Lately my parents have been having a hard time parking their car in the garage because of visual obstructions. I have a circuit here that will use a 5v power supply (probably plugged into the wall, batteries wouldn't last long enough)

    --d1 is a laser pointer
    --r1 dissipates .5V so that d1 runs on 4.5v, and at 200mA (hopefully thats the right value, correct me if I'm wrong) so it should be 2.5 ohms right?

    The problem is, I'm a little bit confused about using not gates. d2 should be a photodiode, so that when d1 shines on it, r2 (which would be a buzzer or some indicator that the light beam has been broken) doesn't do anything. r3 limits the current when r2 doesn't have current through it, and r2 limits current when r3 has no current through it, am I right? r2 May be just a buzzer, or a buzzer and another resistor if the buzzer doesn't run on 5v.

    Hopefully I've explained my problem, just let me know if I'm doing things right. Oh yeah, both r3 and r2 should be 25 ohms right? (5V / .2A)

    Here's a link to my schematic:

  17. Ok, now that I've got the hang of what they're for, and things like DC gain and such, how would you design a circuit and figure out the specs for your transistor? For instance take this circuit for example:

    How would I go about figureing out values for Q1? Would I use Ohm's law, Kirchoffs law, I'm really clueless... I'm sure I'd have to use Ohms law to figure out the amps going through R1, then use the DC Gain to get the current flowing through the Collector-Emitter, then put the proper resistor in front of D1 so that it doesn't blow out right? But then where does all this Vce, Ib, and Ic (and watever else there is) junk come into play? I'm really not sure I understand why you need those ratings  :-\

    Thanks for helpin me out

  18. Ok everyone i tried my best to figure this out, but I came up with nothing. It's sort of hard to search the internet for parts with certain specs, especially transistors. So I need some help from you guys.

    Basically this is a schematic for a (crappy)laser pointer detonator I'm making, just for fun. The light dependant resistor in the top left corner's resistance in full light is 2.2k Ohms, and in full darkness its 300k Ohms. The fuse starter is just a piece of steel wool wrapped around a match which heats up and ignites what ever its touching. I got somewhere with the math portion of figuring this out: Turns out I need the transistor to start conducting once the base-emitter current is at least about 2mA (in full darkness its .03mA and in full bright its 4mA, so I went for just about half way in between). Then once the base current is running to a good amperage, im hoping the collector current should be about 1A (although the more the better

  19. I have a few questions about transistors, so here we go:

    How can you tell how much current must flow between base-emitter to allow current to flow collector-emitter??

    How can you tell which connector on a transistor is the emitter?

    When a transistor gets a small current running through the base-emitter, which then allows current to flow collector-emitter, does the current through the base-emitter get cut off? Or does it keep flowing in tiny amounts?

    One last one: If a transistor has a current flowing base-emitter which then allows current to flow collector-emitter, if the base-emitter current is turned off (by a switch or something) does the collector-emitter current turn off too? Or does it just need a kick start to get going then nothing can stop it except a switch or broken circuit?

    I'm very sorry if my questions are unclear, I'm not very good at describing things  ;D

    Again, thanks for all the help, you guys are life savers (no not the candy  8) )

  20. Ok, I'm not sure if anyone said this yet, but here is how part of lightning works:

    Whichever one is negative (the clouds or the ground, not quite sure) induces the opposite charge on the other thing. If that makes sense. Basically if the clouds are heavily negatively charged, when they pass over the earth they induce a strong positive charge on the surface. That makes the negatively charged ions in the clouds want to travel towards the earth. Then, once enough of those ions have accumulated, they go ahead and do that. Now as i said, it might be the other way around, I'm not quite sure, but this should give you a pretty good idea of how it works.

    The only thing i never really looked at is HOW the charges get so great in the clouds/ground which then induce the charge on the other thing.

  21. Wow man, thanks for that. I didn't realize it only conducted 10mA under bright light. But I was browsing some websites and they had circuits similar to the one you described : a phototransistor drivin a transistor that is rated high enough to get a nice current flowing. Thanks for the help, its much appreciated.

    Also, if you dont mind, what do you mean by 'additional amplification'. I never knew light could be amplified =O

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