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project help

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fkuk

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**broken link removed**
the lm3916 is slightly messed up in the program
it did not have 18 pin chip

this is two halfs of my project

induvidually the both work but
joining together im having problems

when nothing is connectted to pin 5 all leds are on
when pin 5 is connect to ground all led are off
when pin 5 is connected to top half of the output pins (one above capacitor) all leds are on
when pin 5 is connected to bottom of output pins below cap all leds off

when a 20k resistor is attached to pin 5 to ground
when nothing is connectted to pin 5 all leds are off
when pin 5 is connect to ground all led are off
when pin 5 is connected to top half of the output pins (one above capacitor) all leds are on
when pin 5 is connected to bottom of output pins below cap all leds off


can someone guide me in the correct direction to get this thing working
 
when nothing is connectted to pin 5 all leds are on
That is normal because pin 5 has a small positive input current and needs at most 1M ohms to ground to keep it near 0V.

when pin 5 is connect to ground all led are off
Good.

when pin 5 is connected to top half of the output pins (one above capacitor) all leds are on
when pin 5 is connected to bottom of output pins below cap all leds off
That is good.

when a 20k resistor is attached to pin 5 to ground
when nothing is connectted to pin 5 all leds are off
when pin 5 is connect to ground all led are off
when pin 5 is connected to top half of the output pins (one above capacitor) all leds are on
when pin 5 is connected to bottom of output pins below cap all leds off
Pin 5 is the input of a DC voltmeter. 0V turns off all the LEDs and +1.25V and more turns on all the LEDs.
The top output wire of the input circuit is at the +1.5V power supply voltage. The bottom output wire of the input circuit is always at 0V.
 
so how do i get the lm3916 to light up the leds acording to how much sound the microphone picks up

i wired up headphones to the output pins and it is really sensitive and clear

but i need the leds to bounce up and down with the sound in the room how do this
 
The LM3916is just a logarithmic DC (not AC) voltmeter. It can be configured for a wide variety of input voltage levels, but you must use an external full or half-wave audio voltage rectifier to convert the audio amplitude to a varying dc voltage as shown on **broken link removed**.
 
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Run your simulation and see that Q3 is saturated and will not amplify. It also needs to have a collector resistor. Fix it.
Look at the datasheet for the LM3916 to see that you are shorting the pin 7 voltage reference to ground. The pin 8 ADJ pin can be connected to ground instead and the 1k resistor should be from pins 6 and 7 to ground.
 
The preamplifier appears to have a power supply of 1.5V. This isn't enough. The amplifier looks like it was designed to use a supply of about 5V. Q3 has no collector resistor so the LEDs stay off because the output stays low. Q2 and Q3 are wired so all the LEDs are on when there is no sound, and the LM3916 might get a reduced voltage when there is sound. Or it might just go to zero.
 
the microphone circuit was intended to have a set of headphones across the two output pins
would that be the collector resistor or do i need a another resistor

i am going to make the rectifier and see how that goes
 
It is very bad practise to have DC current in headphones. A headphones amplifier should be used.
Of course Q3 needs a collector resistor but it also needs to be biased properly.

Did you fix pin 7 and pin 8 of the LM3916?
 
yeah i connected

pin 6 and 7 to the 1k which is connected to ground

pin 8 goes directly to ground


and how do i fix Q3 what resistor value should i use for collector
 
The LM3915 and LM3916 display audio signals much better if a peak detector circuit is used as shown in their datasheets.
In my Sound Level Indicator project I used a low voltage, low current single supply dual opamp to be the preamp and peak detector. I used a 9V supply but it will work fine with a 3V to 30V supply.

I used an MC33172 dual opamp that has a full power output of 35kHz but if you don't care about high audio frequencies you can use an LM358 dual opamp that has a full power output of only 2kHz.
 

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would it be possible to keep my microphone circuit and at the end attach the peak dectector section from your circuit?
because im doing this for college and ive allready spent a load of money on this

also if i can attach the peak detcector to my microphone circuit can i use a lf351 opamp
because i have quite a few of them

in the lm3916 data sheet on page 11
im thinking of using figure 4 a half wave rectifier
but i like your one better because it does not require diodes and the diodes used in the data sheet are specialised one and in your one it only requires resistors and capacitors that are generalised
 
would it be possible to keep my microphone circuit and at the end attach the peak dectector section from your circuit?
Yes if you use an MC33171 opamp for my peak detector.

[quyote]can I attach the peak detcector to my microphone circuit can i use a lf351 opamp
because i have quite a few of them?[/quote]
The LF351 needs a dual polarity supply for the peak detector circuit in the datasheet.

in the lm3916 data sheet on page 11
im thinking of using figure 4 a half wave rectifier
but i like your one better because it does not require diodes and the diodes used in the data sheet are specialised one and in your one it only requires resistors and capacitors that are generalised
The diodes are ordinary 1N4148 or 1N914 diodes. My circuit uses an MC33171 single opamp or an MC33172 dual opamp that work from a single polarity supply.
 
ok on the left i will have the whole of my microphone circuit

and on the right i will have the peak detector section from your circuit but instead of using a mc33172 i will use a mc33171
do i copy it from C4 330nF and work right
ignoring C3 47uF and the 1k resistor above it

also do i attach the peak desteactor to the top of the capacitor on my circuit

and do this should hopefully get my project finished?
 
i looked for the mc33172 and mc33171 in my local electronic stores and i can not find them i realy dont want to spend extra money on postage
is there a close alternative or is the circuit around the opamp baised around the opamp
 
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I don't know why you want to use your transistors preamp that will have distortion and poor low frequency response.
If you cannot find an mC33171 then use half an MC33172 or use half an LM358
that has poor high frequency response.
 

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when you say low frequency what is the frequency

as long as it resonds to music and voice. will it?

what the main thing is at the end of the day is that im on a budget but i have to do a project for college
ive spent a bucket load on this
while other people in my class are finding a complete circuits on the internet and copying it word for word and we also have to do a presentation on this and i think they will have no idea what they are talking about
i want to be able to tear down each component and say what it is doing and actually know what i am talking about
 
The value of the capacitor between the mic and the first transistor will not pass low music frequencies because its value is too low.

How did you spend a bucket load on three 10 cent transistors? At Radio Shack where everything is overpriced?
 
no its postage manly that gets you

so does that mean if i attach a larger capacitor there it lower frequencies will pass
 
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Don't you know that the value of a coupling capacitor and the resistance it feeds determines the low frequency response?
The problem is that your transistors have some negative feedback that reduces their already low input resistance.
 
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