LM3914 Question, Help!

[TheSwede73]

Hi again, i know i have asked some of you about this before, maybe im a slow learner

My main question is.

Can anyone maybe take a photo of a simpl circuit with the lm3914, with a potentiometer connected so you can adjust the leds on a bargraph, 10 leds.

I have it connected to a breadboard, but i just dont know how to connect everything...

So, the lm3914, a 10 led bargraph, potentiometer, battery.

Thanks!!

 

[ericgibbs]

Hi again, i know i have asked some of you about this before, maybe im a slow learner

My main question is.

Can anyone maybe take a photo of a simpl circuit with the lm3914, with a potentiometer connected so you can adjust the leds on a bargraph, 10 leds.

I have it connected to a breadboard, but i just dont know how to connect everything...

So, the lm3914, a 10 led bargraph, potentiometer, battery.

Thanks!!

hi,
Connect one end of the pot to +5V and the other end to 0V,, wiper to +5Vinp

 

[TheSwede73]

Thanks!

And " - " from the battery to ground? at pin 2 or am i totally lost here

 

[ericgibbs]

Thanks!

And " - " from the battery to ground? at pin 2 or am i totally lost here

hi,
This a common cause of confusion.

The battery -V terminal is the 0V common connection, drawn as an upside down tree.! OK.?

 

[TheSwede73]

Next question

If i read the schematic it looks like the V- and the +5v (with the pot, between) is connected together... via the dotted line with the capacitor....

I know its much to ask, but could you write excactly where everything connects... i would really appreciate it!

Thanks again!
/Anders

 

[audioguru]

The circuit does not have a V- negative supply. Instead it has +5V, +6.8V to +18V and 0V which some people call ground.
The capacitor with dotted wires has its negative wire connected to 0V and its positive wire is connected to V-LED.
The pot has one terminal connected to 0V and the other terminal connected to +5V.

 

[TheSwede73]

Are you from this world? or the matrix?

Thanks... what would i do... nobody seems to be interested in electronics in Sweden... but i just love it, i dont know so much, obviously.... i have about 20 000 leds, all kinds... but i dont know much about circuits...

Thanks for being there!, i'm so happy!

I hope you don't mind me asking questions, i can't really be of much help myself....


/Anders

 

[TheSwede73]

Still no lights

Hi again!

Is it neccessary with the capacitor?
I just can't get it to work...

I have +5v to one leg of the capacitor, the middle leg on the 5-pin (signal) on the Lm3914.
But then the other leg of the pot seems to be connected to 0V.. where do i connect the (+) side of the leds, the one's that are joined togheter.

Thanks!

 

[TheSwede73]

Sorry

I meant the pot, not the capacitor.. but you got that

 

[ericgibbs]

I meant the pot, not the capacitor.. but you got that

hi,
Does this help.?

 

[TheSwede73]

Thankyou!

I'm sure!, im on my way to buy a lab-powerunit now, i hate messing with batteries that needs recharging and so on...
After that i will try.
But again, is the capacitor needed?

And now i understand that i need two powersources?, didn't get that in the beginning...
One that provides 5 volt and one 9-12V

Thanks again!

 

[ericgibbs]

Thankyou!

I'm sure!, im on my way to buy a lab-powerunit now, i hate messing with batteries that needs recharging and so on...
After that i will try.
But again, is the capacitor needed?
If the LED's are more than 6 inches from the LM3914 then Yes.

And now i understand that i need two powersources?, didn't get that in the beginning...

One that provides 5 volt and one 9-12V
You can use a resistive divider to give the 5V from the 12V.



Thanks again!

Assume your psu is 12V output.
And your signal pot is 10K.
So you have to drop 7V in a series resistor from the 12V...

I'll do a sketch give me a minute.


EDIT:
Connect a 14K resistor from the top of the 10K pot as shown, this will give the 10K pot a range of 5V.

If you only have a 15K resistor, then this will give 4.8V across the pot.

OK.?

BTW: a 220K in parallel with a 15K should give about 14K....

 

[picbits]

Thankyou!

I'm sure!, im on my way to buy a lab-powerunit now, i hate messing with batteries that needs recharging and so on...

Never use rechargable batteries for prototyping unless you're 110% confident the circuit is working and you haven't shorted anything out.

Rechargable batteries give out a whopping great current and will fry/melt/vapourise anything in their path if you've got a short.

 

[TheSwede73]

Thanks!

I have always been using batteries...but from today a labunit..

Wow, much new information here

I will study it, and if you have the time and could draw a new schedule i would really appreciate it, but you dont have to, i have gotten much more help than i deserve already

Thanks!

 

[TheSwede73]

I think i get it!

I will update you about the result!

Thanks for all help!

 

[TheSwede73]

And stuck again, damnit...

Do i have to connect everything like in the picture? like from pin 7 to 6 and so on or are those for other applications?

 

[TheSwede73]

Stuck again, damnit...

Do i have to connect everything on the schematic? the 7 pin with the 6, and the two resistors there or is that for other applications?

 

[audioguru]

It will not work if pin 6 is not connected to pin 7.
Every part and every connection in the schematic has a reason.

The only optional connection is pin 9: Connect it to the positive supply for a bar-graph and leave it disconnected for a moving dot.

 

[TheSwede73]

I see!, i thought this schematic was for many different applications, then i get it..

The resistors from pin 7, are they the same value always, unaffected by the choice of 9 or 12 volts?

 

[ericgibbs]

I see!, i thought this schematic was for many different applications, then i get it..

The resistors from pin 7, are they the same value always, unaffected by the choice of 9 or 12 volts?

hi,
The resistor values shown are from the application datasheet, to suit a 5V input signal and all pins MUST be connected as per the drawing.

The values will suit 9 or 12V operation.

Do you have the LM3914 datasheet.?
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