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Lm3915 Help

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If there were a number of persons interested in this, I would do up a circuit board for it. But for just one person, it isn't very practical.
It is a Very Simple Board, even with that transistor peak detector circuit.
(Although I prefer a IC Peak detector)
Cost of a Board, probably a few pennies, plus the postage.
 
does anyone have a schematic for the peak detector? or is it in the datasheet?

EDIT: I googled for one, does this seem like a good one?
and can I substitute the Bc558 with a 2n3904? I'm going to give this one a shot anyways, if anyone has a better one, I up for it.
 

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Hi Jeff,
You have "found" the same peak detector that I posted a few days ago from the datasheet. I tried it nearly 30 years ago and it worked fine with a single IC.
You can't use an NPN 2N3904, you must use a PNP like a 2N3906, also on the datasheet.

I don't like the way you wired the pot. It will adjust the circuit's sensitivity and the brightness of the LEDs at the same time. What happens to the IC when the pot shorts Vref-out to Vref-adj?
The LED brightness will be extremely low unless you add a lower value resistor from Vref-out to ground.
 
hmm...I thought it was an npn. I used it and it seems to work. although I had to remove the 1uf cap and 1Mohm resistor. I'll try swapping it for the 3906. shouldnt it work the same way though since it is a sine wave coming in?

Also, I used the same circuit that I posted earlier in this thread, but I just added the peak detector (left half of the pic).
 
No Jeff,
Sorry, but I disagree with you.
You used a completely different circuit before, with Ref-ADJ grounded to provide a reference voltage of 1.25V, and Ref-OUT with a 1K resistor to ground to provide an LED current of about 12.5mA.

Also, if you used 1.8V red LEDs and the 12V supply, in the bar mode with all 10 LEDs lighted, the package is dissipating more than 1.28W! Very hot.
The datasheet says, "V-LED must be kept below 7V or dropping resistor should be used to limit IC power dissipation".

Here is your "hot" circuit from before with the IC's pins identified:
 

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I'm not using this IC to drive LED's I have one or 2 blue leds on there for indication so that I know the IC is working, and I'm using the highest output for a clock signal for my 74hc299 shift registers. I"m also running it off 5 volts.
 
Hi Jeff,
That's OK.
I just didn't want anyone to think that your circuit will drive red LEDs.
 
Don't you understand that the dot is moving over most of the LEDs much faster than you can see and is blanked out for half the time that the alternating music is negative.

Use the Half-wave Peak Detector circuit at the input of the LM3915 as shown in its datasheet fed from a DC-coupled mic preamp and it will show a bright moving dot. It moves quickly then pauses long enough at the peak voltage so you can see it. It rectifies the signal so it doesn't blank the negative parts.

My LM3915 is in a socket that is soldered on Veroboard and its DOT display looks like this:
 

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sorry for re-energizing this very old post, but I was just looking at your photo there audioguru, and was wondering if you have scratched the copper off the part of the board that is hiding under the chip? My understanding with that borad is that each column is joined and is effectively one node (as the copper runs all the way down). So, did you have to scratch the copper off so that the pins on the top of the IC chip aren't effectively connected to the pins at the bottom? Or have I completely misunderstood the design of the board?

Thanks, and sorry again for bringin up this old thread.
 
I use strip-board that has parallel copper strips.
I don't scratch it, I use a drill bit to cut a small circle of copper away. The diameter of the circle is a little larger than the width of a copper strip. The perforated holes guide the drill bit. I mark the spots to be cut with a marker pen.
Veroboard company used to sell a "track cutter" which was a drill bit in a plastic handle.

The strips are also cut where I want to finish a line and start a new line, along the same copper strip.

For a few cuts I hold the drill bit in my hand but for many cuts I use my drill press.
 

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ah i see, thats awesome. So basically, you drill into one of the already drilled holes, but with a bigger drill bit, so as to drill through the copper that goes around that hole? What a great idea, much more efficient thatn scratching it away haha. Now that I know that I reckon I can put my veroboard to good use :D. Thanks so much.
 
Buy the proper tool, it's only cheap - and you wouldn't believe how much easier it makes it.

I used a drill for decades, then happened to buy the proper tool - I felt afterwards I had wasted so much of my life! :eek:
 
haha fair enough. Any chance someoe can give me a link toa product description of the right tool? Just so I can see the proper name and what it looks like?

Thanks
 
Can you tell me how to make electret mic preamp for this vu meter?
For my Sound Level Indicator project I used an MC33172 dual single-supply opamp (but an LM358 will also work but will be missing high audio frequencies) as an elecret mic preamp and active peak detector:
 

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For my Sound Level Indicator project I used an MC33172 dual single-supply opamp (but an LM358 will also work but will be missing high audio frequencies) as an elecret mic preamp and active peak detector:

AudioGuru, Just a note: Igazzu Falls in Brazil are FANTASTIC. Better than Niagara Fall.

As to A Preamp, Why not make the SPL Meter on my site. Than you also have a Referenced Sound Pressure Level.

Gary
 
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