Designing a preamp for a PIC

Discussion in 'The Projects Forum' started by nnxen, Jun 25, 2014.

  1. nnxen

    Thread Starter New Member

    Dec 22, 2012
    Hi everyone,

    Forgive me for sounding like newbie here, but we all start somewhere :)

    I'm starting to get quite in to PIC programming and made a few projects with a dev board. One thing I'd like to try tackle now is sampling audio from a simple dynamic microphone. The programming aspect shouldn't be an issue but one thing I am struggling with is designing the preamp. My electronics knowledge is only basic but I'm completely willing to put the effort in and learn!

    I basically need to bias and amplify the microphone input so that it ranges from 0 to 5v (the supply voltage) to be fed to the PIC ADC input. The amplifier needs to have variable gain so it can be adjusted depending on the source. Exactly what the maximum gain would need to be is something I need to look in to (anyone have a suggestion?) I have a new mic on order and will be taking some scope readings from it next week.

    I looked at since it doesn't require a -ve supply unlike many schematics I've seen, but when I simulate it it only seems to get to around 3.7v peak-to-peak before clipping and the "zero" level seems to vary between 2.6v and 3.2v depending on the position of the pot rather than being stable at 2.5v which would be ideal.

    Any help such as links to resources, schematics, easy-to-understand tutorials, or advice on alternative components and designs are all very much appreciated:) I'm eager to learn!
  2. Lestraveled

    Well-Known Member

    May 19, 2014
    Here is an amplifier I designed for my grandson. It runs from a single 5 volt supply. It is stable to a gain of around 50. It works well with his electric guitar and dynamic microphones. If you are using electret microphones then add a 2.2K pullup on the mic side of C1. Oh yea, R4 is 100 ohms.