Sallen Key Low Pass Filter, bandpass filter

[Maglatron]

Hello,

You can set the sensitivity of the LM3914 or LM3915 by changing the Rlo (pin 4) and Rhi (pin 6) voltages.
The Rlo will set the lowest led and Rhi will set the highest led.

Bertus

how do I set Rhi please?

 

[Maglatron]

Hello,

No, The V- should go to the - of the 12 Volts.
The Rhi could be a value between Ref and +12 Volts.

Bertus

I'm just going to leave it at 12v or put a variable resistor 10k

 

[Maglatron]

I think this

 

[Maglatron]

Is it correct?? I think it looks good to go! if not can you modify the diagram to express how it should look please?

 

[Maglatron]

I've got the part in green but have to get it connected to the LM3914! (green part)

 

[Maglatron]

I get why the REF virtual ground is put to the Rlo, it's because 6v is the lowest instead of 0v and the upper limit is between 6v and 12v I just don't know how to set it up

 

[bertus]

Hello,

The Rhi is dependend on the signal you get out of the detector.
Set Rhi in such a way that the maximum of the detector shows all leds.

Bertus

 

[Maglatron]

please can you draw the schematic so I can work it out looking at the correct configuration because I don't understand, I'm lost, I need an image of the circuit running off a 12v source please please please can you do a design of the cascaded bar type LM3914 with the REF virtual ground from the buffer circuit, and the actual ground and resistors, I would be so extremely thankful and will appreciate it I'm just trying to picture it and follow the directions I have read in the documents, but to be honest dont really understand them fully and I think that if I can see how it's done and read back over it, then I will understand

 

[Delta Prime]

I think you missed a bit,

This is true. Thank you for the correction.

 

[Maglatron]

It's like if I know how it's supposed to look and know why it works that way, then I can understand it, but trying to figure it out on my own is like putting together a puzzle without a picture on it! so please provide me with the images I need, cheers

 

[Maglatron]

anyone?? please!?

 

[Maglatron]

I got this far in the chain just need little nudge in the right direction

 

[Maglatron]

for the 9 volt at the beggining I will use a voltage divider Vout = Vin x (R2/R1+R2)
pick R1 to be 10k
9V = 12V x (R2/10k+R2)
solve for R2 = (9V x 10k/12V-9V)
R2 = 90k/3V
R2 approximatly 30k!

 

[Maglatron]

do I just put the REF vitual ground to the Rlo in this video and +V to 12v and ground from the 12V supplt to ground of the chip? cheers I think thats correct but I still don't understand how to set Rhi. So I think you disconnect Rhi from REFout and put a desired voltage, correct?

 

[kellys_eye]

Have you downloaded and read the LM3914 datasheet? It's all in there.

 

[Maglatron]

So I have read and re-read the datasheet and I'm still confused, I can see that VRlo needs to be greater than zero and VRhi needs to be less than 12V so I know how to set the Rlo that bits easy, just put the REF virtual ground. But how do you set the Rhi to 12v because Rhi and refout are connected ? cheers

 

[Maglatron]

I recon I'm overthinking it can you screen shot and red box the part that tells me where and how to set Rhi to 10Volt please?

 

[Maglatron]

Vout_ref = 1.25×(1+R1/R2)
10V = 1.25×(1+R1/R2)
solving for R1/R2
R1/R2 = (10V/1.25)−1
R1/R2 = 8−1
R1/R2=7
choose specific resistor values that satisfy this ratio
R1=1kΩ and R2=7kΩ
Does this look right?
I think this maybe right!!

 

[Maglatron]

It was right infront of me the whole time, sorry for that guys, it's just clicked!

 

[Maglatron]

Have I overlooked anything other than that which I did? cheers