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thzzz, rili sorry for repeatedly making silly english mistakes... English is not my mother tongue leeeeeeee... "earthed" ;D, it should be "grounded" :-* So now we have both variable voltage-gain pre-amplifier and the variable volume control. Both accounts for the sensitivity or setting of the musical shower?~

I will connect pin 9 to pin 3 for bar mode ;D thanks very much for your help ar, :) I have some questions about your diagram 1) Is the word "Rectifier" supposed to be under the diode and capacitor, and the word "Preamplifier" be under the transistor and resistors? 2) There is just one input for the triangle and I suppose it's a buffer gate rather than an op-amp :P As far as I was taught, a buffer gate is two not gates in series. the output of a not gate is independent of the input. it just follows that the input is low then output is also low, input is high then output is also high. but a buffer gate does not amplify the input in ratio... Is what I taught correct? If so, then the circuit cannot serve as a volume detector!? 3) the v- in the diagram is earthed?

I just put P.22 of the factsheet http://www.alltronics.com/download/LM3915.pdf#search='LM3915' in the written part of my project. replacing the word "LOUDSPEAKER" by "MIC INPUT", the word "Output Amplifier" changed to "Amplifier and Rectifier(+filter)" is it okay!? leaving the details of amplifier and rectifier not mentioned.

thanks, I have some problems drafting the circuit regarding LM3915 just silly problems. http://www.national.com/ds/LM/LM3915.pdf according to page ten of this factsheet FIGURE 1, the amplifier and rectifier. the input,,, only one input...>!?!?!?!..<<??!? how can I connect a microphone to it... a microphone,,, two wires... only one place for input...... and one for output,,, one output to SIG5 is okay,,, but only one input... how to draw? also, if i want to voltage gain to be variable, which, R1 or R2, R3, R4 should I change to variable resistor? I know it's not the page's error,,, just my poor knowledge about circuit... thanks.

thanks~ where can I find the LM3915 datasheet? I'll have to do the written part of the project, I'll be using the diagram below to briefly illustrate the flow of the circuit: Click here, circuit Then in practice, I'll use the IC, do some calculations on the values of capacitance, resistors. Do you think it's okay? moreover, what do you think I can put in the other side of the electromagnetic relay? I propose using a big water tank and some tubes. What I have to do is just control the opening and closing of some switches or valves. If I couldn't figure out how to set a valve circuit, I'll have to end up showing LEDs, which is much less fun than seeing a musical water fountain:( thanks

then do I have to use a specially designed rectifier? moreover, as I mentioned in the last reply, u have a brief idea of my project. but will the rectifier give a very smooth DC even the amplitude is varying? thanks vy much. bed time~

Thanks vy much again. Perhaps it'll take me some time to digest :-* I'm doing a project trying to control the switches so that there'll be some kinda musical fountain with a music input from a CD. A microphone version is for demonstration. when people sing with the microphone,,, switches open and close. The CD version need a variable resistor I suppose because input from CD is fed by user where the user can adjust the volume. This is a high school project and I'm trying to achieve the task above using the simplest way (difficult ways i'm not capable of that,,,:p) That's why I chose to use amplitude instead of frequency though i'm afraid amplitude won't show much variation.>< About the problem being discussed by you guys!~! I know the amplitude of a song is always varying... that's why I'm quite worried><

Thank you very much. i've been wanting to know the voltage generated by speaking to a microphone!!!~ I still have a few problems: 1) why do I not have to use the bridge rectifier but a single rectifier diode instead?~ 2) Should I use a PreAmp before the rectifier? Would it make the circuit not sensitive enough because there'll be noise in the PreAmp? moreover, is that any preamp will do the job provided that it amplifies the voltage by 260 times? 3) Actually the circuit will be extended so that different amplitude will activate different switch. Sensitivity is quite important, do you think my circuit will be sensitive enough so that when people are singing songs, the circuit reponds differently to different amplitudes?~ the variation of amplitude is a song is large enough?~ 4) Actually i'm not very familiar with Transistors, so is it okay if I just use the buffer gate?~ haha, thanks very much~~~ :-*

Circuit Diagram Here sorry again,,, I know I've been quite weak at electronics. About the circuit diagram: Input from Microphone -> Retifier/Filter Circuit to convert the input wave to steady direct current of voltage similar to amplitude of wave -> Variable Resistor -> Potentiometer to adjust -> if Input voltage is high enough, activate relay questions: 1) any bugs? feasible? 2) I wonder if the voltage of microphone, as we speak, is enough to drive a circuit !@???@_@ other questions later thanks very much >< :-[

this is what I mean filter circuit Voltage Follower

thanks, yes you're right. IF the amplitude of sound exceeds a certain level, it activates an electromagnetic relay. I have several questions: 1) Is Voltage Follower = two "not gates" used in conjuction? 2) Do I have to amplify the amplitude of sound so that the voltage is large enough? 3) Is there any bugs/logic error in the circuit? 4) Any improvement or more convenient ways? Thanks~ btw, if I want to make use of the frequency of sound instead of amplitude, how can I make it? thanks~!!!

The link is okay now :'(,,, pls help me. thanks :-*

I'm very sorry,,, can you open a new browser and paste the link to see it... I don't know why it is like this too><

oh, sorry, if you don't see the diagram, open a new browser and paste the link there ><