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UAF42: Band Pass Filter

Christopher James
Intellectual 880 points
Part Number: UAF42
Other Parts Discussed in Thread: LM4766, LM555

The Bandpass Filter UAF42 diagram is based upon the plastic 14 Pin Package and there does not appear to be one for the 16 Pin SOIC surface mount package.


I have attached an amended version of the filter with what I believe are the correct Pins for the 16 Pin package. Can you, please confirm or otherwise?

My input frequency voltage is only circa 1.5v but I am proposing to run the UAF42 from a 15volt parallel rail supply. Will this present a problem?

Should I have a decoupling capacitor between V+ Pin 11 and Ground , and if so will a 1uF capacitor be adequate?

On some of the UAF42 filter diagrams VIN2 is connected to ground Pin 12 via a RQ which varies in value. The two square wave frequencies I am converting into sine wave are circa 40Hz and circa 530Hz. Should I add a decoupling resistor between Pin 4 and Ground, and if so, what size(s) should I use, please?


Thank you so very much.


CJJ


  • 0
    Guru 140200 points

    Hi Christopher,

    I hope the following simulation will answer your questions:




    christopher_uaf42e.TSC

    No, I would not add a cap in parallel to RQ.

    Connect a decoupling cap from each supply voltage to signal ground. Use at least 100nF/X7R.

    Kai

  • 0 in reply to kai klaas69
    Intellectual 880 points

    Dear Kai,

    I cannot thank you enough, I am so very grateful!

    I have little understanding of electronics per se, and thus with our technician poorly in hospital I have been floundering.

    Thus, your kind assistance cannot have come at a better time.

    Thank you once again.

    Christopher J James
    Director

    PS May I substitute UAF42AUE4 for the UAF42E in the Diagram, please?

  • 0 in reply to kai klaas69
    Intellectual 880 points

    Dear kai,

    Is it too much to ask how I might connect the output from Pin 8 to an LM4766 amplifier as recommended, please?


    Can you also, please advise what external Resistors and Capacitors would be required?


    My final destination has an impedance of typically 175 to 200 Ohms.


    I cannot thank you enough for your kind help.


    I am sincerely grateful.


    Christopher J James

  • 0 in reply to Christopher James
    Guru 140200 points

    Hi Christopher,

    I would use this circuit:

    Choose RM=18k and CM=100µF for the muting circuit. You can close S1 permamently, if you don't want to mute the LM4766 by hand. For Rv I would take a multiturn cermet trimmer from Bourns. 

    Connect pin 8 of UAF42 to the audio input terminal of above circuit. Turn Rv fully down before you power on the UAF42 and LM4766. Then, adjust the output level as desired.

    Kai

  • 0 in reply to kai klaas69
    Intellectual 880 points

    Dear Kai,


     Amongst my colleagues, we define people either as "service to others" or "service to self". You are without debt a "service to others" for which I am exceedingly grateful to you.


    You will probably have seen my request for help with the 555 timer circuit, which is the last unknown for me.


    Would it be possible for you to evaluate the values of Ra Rb and Rl for the LM555, please? I also assume that the output from LM555 is at Pin3?


    Thank you once again.
    Christopher J James

  • 0 in reply to kai klaas69
    Intellectual 880 points

    Dear Kai,

    I neglected to add, the timing interval I wish to achieve, to switch from one frequency to the other is 5 minutes, please.

    Thank you so much.

    Christopher

  • 0 in reply to Christopher James
    TI__Guru 61211 points

    Hi Christopher,

    Enclosed are two square wave generators. The generated frequency is pretty close to 40.6Hz and 528Hz, but they may need some fine tuning.

    Best,

    Raymond

    LM555 528Hz squarewave 02032020.TSC

    LM555 40.6Hz squarewave 02032020.TSC 

  • 0 in reply to Raymond Zhang1
    Intellectual 880 points

    Dear Raymond,

    I used to run 555 timer circuits, thank you, until I started to programme Epson Crystals. The circuit only involves a voltage reduction, the crystal, a Ripple Counter and a few capacitors and it is accurate for both frequencies to 4 decimal places.

    I will certainly look at the circuits, but I am loath to change what is working non stop 24/7 for the past two plus years.

    I realise at some point in the future the availabilty of the Epson Crystal will fry up, but that is hopefully a liitle way off as I have over 1000 in stock.

    Christopher

    PS Would it be possible to respond to my queries about the links carrying RL, please?

  • 0 in reply to kai klaas69
    Intellectual 880 points

    Dear Kai,

    I wanted to thank you again for all the help that you have so kindly given me.

    I thought you might like to see what is hopefully my final circuit for the UAF42.

    Thank you once again.

    Christopher

  • 0 in reply to Christopher James
    Guru 140200 points

    Good luck, Christopher!

    Kai

  • 0 in reply to kai klaas69
    Intellectual 880 points

    Dear Kai,

    Thank you.

    Christopher