LM3915 LED VU meter problem - pictures included

[bychon]

I wooda never guessed that Vce of the transistor would be 1 diode drop of voltage, but that's the whole principle of how it works.

 

[Gaichuke]

Damn, I didn't have any pots at hand, I'll have to pick up some tomorrow. Maybe I'll try it anyway with something that should give line level output.

What would the best way to have audio source in these kind of circuits anyway? For example coming from a mp3 player? Strip off other end of male-male 3.5 mm plug, put the other end in mp3 player, then put either channel from the stripped end to audio input?

 

[bychon]

The coolest thing about this chip is that it will work with nearly anything. It's adjustable. I used one for a 100 watt church PA. It will work just as well with a 3 volt MP3 player.

 

[ericgibbs]

Damn, I didn't have any pots at hand, I'll have to pick up some tomorrow. Maybe I'll try it anyway with something that should give line level output.

What would the best way to have audio source in these kind of circuits anyway? For example coming from a mp3 player? Strip off other end of male-male 3.5 mm plug, put the other end in mp3 player, then put either channel from the stripped end to audio input?

hi,
Do you have a 1megohm resistor on the shelf.?
If yes, then
As a test, put the circuit exactly as it was without the new 5K pot.

Momentarily connect the 1meg from pin #3, to pin #5, ALL the LED's should light

 

[Gaichuke]

It doesn't work, at least with mp3 player and without the pot. I presumed it should've worked at least somehow even without the pot, but no.

I think I have a problem with the audio input, it's at the moment just 3.5 mm earplugs, from which I have stripped of the earbuds, and just plugged left one to the breadboard. What kind of audio input I should have for these kind of circuits?

 

[ericgibbs]

It doesn't work, at least with mp3 player and without the pot. I presumed it should've worked at least somehow even without the pot, but no.

I think I have a problem with the audio input, it's at the moment just 3.5 mm earplugs, from which I have stripped of the earbuds, and just plugged left one to the breadboard. What kind of audio input I should have for these kind of circuits?

Did it work with the 1meg from pin 3 to pin 5.?... did any LED light.?

I wouldnt worry about the MP3 or earbuds until the LM3915 works on the static test with the 1meg test resistor...

 

[Gaichuke]

Did it work with the 1meg from pin 3 to pin 5.?... did any LED light.?

I wouldnt worry about the MP3 or earbuds until the LM3915 works on the static test with the 1meg test resistor...

I actually did find a 1 meg resistor. Would this work with the original schematic and without audio signal?

 

[Gaichuke]

Ok, here's the present configuration and photo of the real board too.

I used a 1M resistor and put it between pins 3 and 5, but nothing happened. I tried both with audio signal and without any audio signal in.

 

[ericgibbs]

Ok, here's the present configuration and photo of the real board too.

I used a 1M resistor and put it between pins 3 and 5, but nothing happened. I tried both with audio signal and without any audio signal in.

hi,
Please do the following test.

Unplug one of the LED's, use a 1K from the +12V rail and connect one wire of the LED in the end of the 1K and the other led wire to 0V. [ try the led both ways around if it dosnt light]

Lets see if you have the LED's working OK.

Like this image.

 

[Gaichuke]

Yep, leds work alright individually in that kind of circuit.

 

[transistor495]

Are they blue LED's? The circuit looks fine for driving'em.

How you are connecting the mp3 player 3.5mm jack? Check this image. According to that you've to find the proper pins at the backside of the connector plug.

**broken link removed**

 

[ericgibbs]

Yep, leds work alright individually in that kind of circuit.

ok,
Another test,
Connect pin #7 to pin #5, ALL the LED's should light.

If not, the LM3914 maybe 'dead'.

Let me know what you see.

Do you have a test voltmeter,?

Forget about MP3's until we get the LM3915 working.

 

[Gaichuke]

Ok, I put a jumper wire between #5 and #7, but nothing happened. I also tried this with another LM3915 (I replaced just this on the circuit) but nothing happened here either. I'll get my voltmeter back tomorrow, I sure could use it right now...

 

[ericgibbs]

Ok, I put a jumper wire between #5 and #7, but nothing happened. I also tried this with another LM3915 (I replaced just this on the circuit) but nothing happened here either. I'll get my voltmeter back tomorrow, I sure could use it right now...

hi,
I have looked at the photo and cannot see anything that could be wrong with the breadboard.

When you get the voltmeter, check the 12V, also pins 6 & 7 should be about 1.25V, pins 2, 4 and 8 should be 0v.
Pin 5 should be about 0.6V

The cathodes of the LED's should be about +12V.

Lets me know.

 

[Gaichuke]

I got a loaner multimeter and I tried it to my circuit. I'm not quite sure how to measure with it, but here's what I did:

Red (+) pin from the multimeter to the pin in the chip
Black (-) pin from the multimeter to the circuit ground

12v works, I get about 12.3V through, and all the pins give 9.6V measurement. I think I'm doing something wrong.

I thank you for the patience to answer these...

 

[ericgibbs]

I got a loaner multimeter and I tried it to my circuit. I'm not quite sure how to measure with it, but here's what I did:

Red (+) pin from the multimeter to the pin in the chip
Black (-) pin from the multimeter to the circuit ground

12v works, I get about 12.3V through, and all the pins give 9.6V measurement. I think I'm doing something wrong.

I thank you for the patience to answer these...

hi,

Its sounds as though you have no 0V connection to the LM3915 on the breadboard.!!!

EDIT:
Look at pin #2 the 0V pin.... take out the IC and check for a bent pin

 

[Gaichuke]

This is so weird. When I test the chip pins with the multimeter, LED number 9 lights up very faintly. Except when testing pin #1...?

 

[ericgibbs]

This is so weird. When I test the chip pins with the multimeter, LED number 9 lights up very faintly. Except when testing pin #1...?

Look at my edit, Im sure you are losing pin 2 to 0V.!!

 

[Gaichuke]

I checked, it looks fine. I also tested the other chip I have, but both of those are giving me same measurement values.

 

[Gaichuke]

I changed the jumper wire for pin #2 to a longer one and I also changed the spot where it goes. Now pin #2 is 0V, but all the others are still 9.x