[again, microphone input high school project]

Hi Zgnoh,
It will look good connected as "bar mode".
I'm glad to help you.

1) I think the word "rectifier" should be changed to "half-wave peak detector", which is the transistor, diode, associated resistors and capacitor.
2) The triangle is the preamp circuit. It is an opamp with a gain of a few hundred, with its inverting input inside the triangle and used for negative feedback to determine its gain. The opamp's non-inverting input is the preamp's input.
Digital logic gates can't be used for audio because they only switch high or low. They would sound like "click, click" or "buzz, buzz". Audio amplifiers are linear and smoothly reproduce all sounds and levels.
A new form of audio amplifier is becoming available. It switches its output at a very high frequency that you cannot hear, and uses duty-cycle changes in its output switching pulses to reproduce the audio. These amplifiers operate in "class-D" and the duty-cycle changes in their pulses is called "pulse-width-modulation".
3) V- is a negative power supply. It is used because the input to the LM3914 must be positive only but at ground (not called earthed) with no signal. The output of the preamp must also be at ground with no signal. Therefore, the output of the preamp must swing symmetrically above and below ground with audio, and since it must swing below ground (negative voltage) it must have a negative power supply in addition to a positive power supply.
The half-wave peak detector is called "half-wave" because it responds only to the positive swings (half-waves) of the preamp's output. The negative half-waves of the preamp's output are ignored, but still must be present in order for the preamp's output to be at ground with no signal.

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?~

[again, microphone input high school project]

Hi Zgnoh,
Oops, page 22 says that the LM3915 was discontinued in 1999, I just checked and the LM3914 is available and works the same but with a linear, reduced range.

You must watch your english when talking about inputs and outputs. The microphone's input is your voice, certainly not its electrical output!
Don't forget about the preamp.
I gathered the circuit for you here:

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?

[again, microphone input high school project]

Hi Zgnoh,
The LM3915 isn't connected to the microphone, it is fed from the volume control like the left triangle in your previous diagram. The volume control is R2 of the "Half-wave peak detector" circuit in figure 1 in the datasheet. The half-wave peak detector circuit is DC-coupled from the output of a preamp circuit you still need. The preamp needs a gain of a few hundred and its input is the microphone.

It ain't simple but you're getting there.

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.

[again, microphone input high school project]

Hi Zgnoh,
At the bottom of this page is a link "WWW Search" to the Google search engine. You can enter part numbers, circuit names or anything. I entered LM3915 and it linked to this datasheet: http://www.national.com/ds/LM/LM3915.pdf
You will see that it has 10 outputs arranged in steps of amplitude of the input. The 1st output is activated with a low-level input. The 2nd activates with more input amplitude and so on. It needs only 2 resistors to be calculated, for its maximum input voltage range and the brightness of its LEDs.

On your drawing the left triangle is the LM3815. You show one output driving a relay. You can draw more outputs on the LM3915 driving more relays up to ten.
Each relay can activate an electrical water valve that are used for timed sprinklers for example.
For your demonstration use LEDs instead of relays.

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.

[again, microphone input high school project]

Hi Zgnoh,
It would be cool to see your water fountain squirt by the various levels of music. With most pop music it would squirt to the beat of the music!
1) The LM3915 can have a switch to select a single output called dot mode when it lights LEDs, or bar mode when it lights all LEDs below the one that it is indicating. The outputs of the LM3915 can drive electrical water valves or relays to drive them.
2) You can put a volume control on it to adjust the range of input.
3) With CD input you reduce the gain of the preamp but the circuit still needs a rectifier circuit and filter cap.
4) A very simple rectifier circuit is shown on the LM3915's datasheet that works much better than just a single diode.

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

[again, microphone input high school project]

Hi Kevin,
Of course you will get DC out of the rectifier and its filter capacitor when it is being fed many volts of signal from the mic preamp. That is what a rectifier is for.

Also, of course the changing level of the signal will also change the level of the DC, but the rectifier can be designed for average-responding and have a big filter cap to smooth any quick level changes. You can even design the rectifier to have adjustable attack and release times if you want.

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~

[again, microphone input high school project]

Hi Zgnoh,
1) You only need to rectify the AC audio into smoothed DC. A single diode will do it with a filter capacitor.
2) A single rectifier diode needs at least 130 times the voltage from a microphone to turn-on, so of course the microphone's signal must be amplified by a preamp before being rectified. When you build the preamp, use parts (an audio opamp) designed for being used in a low-level, low-noise preamp and there won't be any noise.
3) Since your circuit needs to detect different sound amplitudes and give separate outputs for them, you should use an LM3915 bar-graph IC which is designed to drive 10 LEDs but can also be used as your switches. Then you don't need transistors or "buffer gates".

What are you trying to do with different levels? The microphone output for a group of people singing at a distance from it will be about the same level as a single person singing or talking fairly close to it. Just listen to a good PA system, its output level is always about the same.
You can design the preamp and LM3915 to have as much sensitivity as you want. The circuit can activate a switch if a pin drops. But it will also activate when a truck drives by outside.

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><

[again, microphone input high school project]

Just one little bug: The microphone needs a preamp.
The output voltage of a microphone is about only 20mV if you shout closely. The voltage requirement of the rectifier bridge is at least 1.3V. A big difference of 65 times. If you talk normally at a normal distance from the mic, the difference is about 260 times. So the preamp must have a voltage gain of about 260.

You don't need a bridge rectifier, a single rectifier diode will be fine.
You probably also don't need the inductor, 2nd capacitor and rheostat. Just connect the potentiometer directly to the output of the rectifier diode and the filter cap.

The "buffer gate" can be an ordinary PNP transistor, with a power supply for it and for the preamp.

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~~~ :-*

[again, microphone input high school project]

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 >< :-[

[Please comment on my project >< thanks~]

this is what I mean filter circuit


Voltage Follower

[Please comment on my project >< thanks~]

I am only guessing here, but it looks like you want to activate a relay with the amplitude of the sound.
Is this correct?

MP

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~!!!

[Please comment on my project >< thanks~]

Hi,

I can

[Please comment on my project >< thanks~]

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

[Please comment on my project >< 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><

[Please comment on my project >< thanks~]

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

[Please comment on my project >< thanks~]

There is an input current from a CD or a microphone.
Then if the amplitude of the sound exceeds a certain level, it activates the switch opening circuit to open a switch.
The circuit diagram is here, pls click.

Is there any mistakes/flaws with the circuit?
moreover, is the "Voltage Follower" correctly used? I suppose a voltage follower = two "not gates" in conjunction. is it like that?

Thanks very much. I know this is just so simple as high-school level.

[How to use a PID circuit to regulate temp.?]

Hi zgnoh,

I found this (http://www.engin.umich.edu/group/ctm/PID/PID.html#introduction) hope it helps :).

Thanks very much. Also thanks for redirecting ;D
In case i have any other/further problem. May I ask for help?
I don't know how to use the PID, how to connect it with other stuffs?

[How to use a PID circuit to regulate temp.?]

How to use a PID (proportional, integration, differentiation) circuit?
Is there any pictures showing how it is connected and what is its use?
thanks~

[Need help on a project changing the strength of water of shower.]

I haven

[Need help on a project changing the strength of water of shower.]

Hi zgnoh,

There are two ways to go with this I guess. One is to start with pressurised water (what you normally have in the pipes) and try to control this with a valve. The second is to try controlling a pump to change the pressure fast enough to follow the music. I am not sure how this will turn out but I would try something like a light organ circuit to control an electromagnetic valve instead of a lamp. You have to be careful though, the water pipes might not withstand the pluses in the long run. To make a magnetic valve more

[Need help on a project changing the strength of water of shower.]

Hi. I'm a newbie, just a teen with very limited knowledge about Electronics.
I'm recently doing a project, trying to make the strength of water of shower change according to the beat of music or something like that.
I propose the music is from a CD player or what and can be connected to the shower tube if necessary... Does anyone get any clue how to start with that?

I actually proposed closing the circuit when water flows in the shower, then the user turns on the CD player...
a few problems arise:
1) How to make the CD player turns itself on and plays without the user pressing the bottons?
2) How can I make the strength of water change in respects to the beat, amplitude, or whatever of music?

My questions may not be very clear, but you're welcome if you get any idea or suggestion or any guide or clue to how it could be established.
I'm just a newbie or even you may say know nothing about electronics. I really need your help ><
Thanks very much!!! really emergency~!