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Hello everybody.

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.

Preparations

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)

butterworth

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