again, microphone input high school project

[Kevin Weddle]

Audioguru, I did some experimenting and found that I was wrong. It seems that a triangle wave is perfect to charge the diode capacitor combination. If even you increase the frequency, the greater DC you have. I was under two impressions. One was that there needed to be more DC delivered to the load like during the peak of the sinewave. I also thought that the triangle would not give enough DC when a triangle was applied. We all learn something. However, when there is a load, there is a DC difference between the sinewave and the triangle, but it is a distinct small difference. And I wonder how that could be. Maybe I am not able to get the peak of the voltage because of the rate of change of the triangle. There is a small voltage divider that exists between the re of the diode and the capacitive reactance. Also I don't think it is because of the discharge because there is little ripple. The voltage divider would explain the up to .2 DC voltage difference.

[audioguru]

Hi Kevin,
Thanks for admitting your error.
If your triangle wave and sine wave have exactly the same frequency and peak-to-peak voltage, the difference in rectified DC voltage is probably due to the different amount of time that the different waves spend at the peak.
The triangle wave spends very little time at its peak voltage. As soon as it reaches the peak, its voltage reduces.
However, the sine wave spends considerable time at its peak voltage so the filter capacitor has a long time to completely charge.

[zgnoh]

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.

[audioguru]

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:

[zgnoh]

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?

[audioguru]

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.

[zgnoh]

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?~

[audioguru]

Hi Zgnoh,
Many elecrical appliances are earthed for safety. Big radio transmitters are earthed so that their antennas work correctly. But your project doesn't have to have its ground common connection earthed.
When you connect something to the earth you connect it to a cold water pipe where the pipe enters the building from outside, or connect to a long metal stake in the ground outside.

The preamp will have its gain fixed at a few hundred and you adjust the sensitivity with the volume control.