Oscilloscope circuit

Discussion in 'General Electronics Chat' started by Jost Reberc, May 23, 2016.

  1. Jost Reberc

    Thread Starter New Member

    May 16, 2016

    I am trying to understand a circuit of the open-source oscilloscope project because I want to build something similar, but there is one part which I don't get exactly.
    This is the schematics: http://essentialscrap.com/dsoquad/DS203V2.png
    So after the second multiplexer in the input section there is "final" operational amplifier, from which output goes to multiplexer and then to ADC. What I don't understand is the circuit which is connected to the positive input of that operational amplifier, and especially why is there connection (red V1 mark) to the processor (I looked up the input pin of the processor where this V1 is applied and it is ADC or standard I/O).
    Does anybody have idea what is the purpose of this output ? Isn't it dangerous for the processor if higher negative voltage is applied to oscilloscope input?

    Another question I have is also why is output of CHa connected to mux of CHb and vice versa?

    Thanks for replies, Joost
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
    If it is an open source project, there must have been a huge community of contributors, com mentors and builders. Why don't you ask the team that developed it? Is there something unpleasant / incompetent with that community?
  3. AnalogKid

    Distinguished Member

    Aug 1, 2013
    Since V1 and V2 go through 2-pole lowpass filters, they might be PWM DC offsets, used to subtract out large DC components in the input signal.