This post is in english again, as my first article about LXI devices was. So, if you need any translation (german for example) use the Google translator please.
Today I am going to demonstrate how to use LXI capable instruments to perform automated measuring on electronic circuits. We will analyze the cutoff frequency of a filter circuit with the help of remotely controlled devices and a little bit of C++ and JAVA.
Since I am a little bit addicted to analog synthesizers, I am currently building such a thing. At the very moment I am concerned about the signal filtering with a so called voltage controlled filter. A voltage controlled filter (which I will call VCO from now on) is an active filter based on an operational amplifier and in my case an active low pass. What distinguishes this filter from a regular one is, that the cutoff frequency can be adjusted with a control voltage. This behaviour is desired because we want to control this filter from a MIDI sequencing application.
But first for the circuit we are using in this little experiment, a voltage controlled 2-pole Butterworth low-pass filter: (taken from the LM13700 datasheet of National Semiconductors)