my led to music circuit

Hi, I've received feedback from forum members on this, but with just a description. I think my intentions were misunderstood so I drew up what I think might work. I'm looking to light up segments from left to right with the intensity of music from a line level car deck. Ultimately lighting them all up. I have changed the string of 3 leds to a string of 4 which will also have the 27ohm not 180. The strings make up letters of a brand of audio equipment. All input is welcome. Thanks

Your math doesn't add correctly.
You have up to five LEDs in series, and each is rated at 3.2V. Then 5 x 3.2V= 16V and a little more is needed for the output saturation voltage of the IC. You don't have enough supply voltage for five LEDs in series.

Why have current-limiting resistors in series with some strings of LEDs when the IC's outputs could do the current-limiting if you add a single resistor between pins 4 and 5.

Why use AN6877 ICs that have a small linear input voltage range? You should use AN6878 ICs that have a wide logarithmic input voltage range that matches the logarithmic loudness response of our hearing.

Thanks audio G, I new I'd be short on power for 5 leds thats why I didn't put R's on that string. I guess I'll knock them down so all strings have 4, then I could just use 1, 27ohm between 4&5? I am unfamilier with this ic and the logarithmic 78. How does it differ? I guess it would be the same hook up? Does the rest look o.k.? Also, on my input I just need the + lead of my rca cable and not the -, right. Thanks, I was hoping you'd see this, Adown

adown said:

Thanks audio G, I new I'd be short on power for 5 leds thats why I didn't put R's on that string. I guess I'll knock them down so all strings have 4, then I could just use 1, 27ohm between 4&5?

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Four x 3.2V= 12.8V and a little more is needed for the output saturation voltage of the IC. Then they won't light when the engine is not charging the battery. Use a max of three LEDs in series.

The datasheet is too brief to say what is the output current with a 27 ohm resistor between pins 4 and 5. 27 ohms would probably cause the IC and LEDs to blow up. The datasheet says that 300 ohms makes 18mA at each output which is fine.

I am unfamilier with this ic and the logarithmic 78. How does it differ?

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I am used to National Semi's LM3914 and LM3915 and their datasheet is clearly explained in English, not an abbreviated translation from Japanese.
A linear range is very small and a logarithmic range is wide enough to see changes clearly.

I guess it would be the same hook up?

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I only glanced at the datasheet. You should look at it carefully.

Also, on my input I just need the + lead of my rca cable and not the -, right.

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RCA inputs don't have + and -. They have a signal wire in the center and a ground wire as the shield. The signal wire and its shield both must be connected.

Ok, I've decided to go with the lm3915 hoping you know it like the back of your hand. I've changed the strings to 15 strings of 3 each led's. I went to national web site and found a audio power meter although drawn for dot mode. I need to cascade 2 drivers for the # of led strings. The only cascaded bar mode I found was this vu meter. I was hoping it is an easy fix to use in my app. Check drawing, red is out, green is what Im hoping to do. I do realize I will have to change the ref for 3 led's as opposed to 1. Any help is appreciated. I called my former college prof. then sent him data sheets and a proposed drawing, and never got a reply. This is over my head, but I'm not afraid to let the smoke out of a few components to get it done. tHANKS, Adown OH, also bad choice of words on the rca's I was just being general.

Using a single LM3915 with 10 LEDs will have a range of 30dB which is a lot. More LEDs will just be lighted all the time in the bar mode unless you play very quiet classical music.
You should add the simple "Half Wave Peak Detector" circuit to the input with an input level control.
You should add a resistor to the supply for the LEDs so it can share some heat with the LM3915.
You don't change the reference when a different number of LEDs are in series because the outputs have current regulation which is the same with 1 LED as with 3 LEDs in series.
My Sound Level Indicator project uses an LM3915, has a microphone for its input and is powered with a rechargable battery or from the charger.

I wish I could use a single 3915,( I would have had it done by now) but I dont have the voltage to run more than 3 leds per string and I cant cut it down any smaller. Are you saying to run your circuit with the HW peak detectorand a led resistor or that vu meter in my post with my changes and your additions. Isn't the hw peak det. for applying a/c input? I have that drawn out and center tapped 12-20 v dc. Thank you, Adown

adown said:

Are you saying to run your circuit with the HW peak detector

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If you don't use the simple Half-wave Peak Detector for the audio input, then the LEDs will just be a dim blur. The peak detector slows down the level changes of the LEDs so that your eyes can follow them.

and a led resistor

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Maybe your IC won't get too hot. If it does then add a resistor in series with the supply line to the LEDs.

or that vu meter in my post

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It has an LM3916 VU meter IC and an LM3915 so the total range is 40dB. Two cascaded LM3915 ICs have a range of 60dB.

Isn't the hw peak det. for applying a/c input?

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No, the simple Half-wave Peak Detector that uses a transistor is for the audio input. The power transformer, rectifiers and large filter capacitor are for AC power.

O.K., I think I'm ready. Off to the electronics dept. Thank you Audio G for all your help. I think I can do this. I'll re-post with the outcome. Thanks again, Adown