Here you find learning material in the form of circuit simulations, that lead you to the understanding of amplifiers and other signal conditioning circuits that we use throughout the course. Feel free to experiment with them, they are editable and saved via the encoded URLuniform resource locator – a human readable web address which is looked up by the →DNS and translated into an →IP Address. You cannot destroy them and it is easy to share edited versions. Here is an introduction to the circuit simulator.

• The foundation of understanding electric circuits is Ohm's law.
• We can calculate series and parallel resistances with Ohm's law:
• A very powerful concept is the voltage divider, it allows us to attenuate (but not amplify!) any voltage in any circuit
• We will use the OpAmp (=operational amplifier) to amplify the small signals from our microphones to usable and less noisy signals before we digitize them in the computer. The opamp (= operational amplifier) is a three port device and its circuit diagram is a triangle. It has a positive and a negative input terminal and an output terminal. The most basic opamp circuit is the "comparator".
• the opamp's output can also directly follow one of its input voltages, but providing more current. This is the basis building block of opamp based amplifiers and is called "voltage follower" or "buffer".
• once you provide a voltage divider circuit in the feedback loop of an voltage follower, you are able to control the gain of the output port. This means the voltage of the output can be a scaled version of the input, either attenuating or amplifying the input voltage. Depending on whether the voltage divider is applied on the positive or negative input, the output is an inverted or non-inverted version of the input voltage. The two basic building blocks are shown below.
• We can use a special configuration of the Opamp together with a capacitor as a simple oscillator. The following simulation is a square wave oscillator. The capacitor gets constantly charged and discharged from the output of the opamp. At the positive input terminal, there is a voltage divider, that divides down the output of the opamp in half. Since it is positive feedback, the opamp will drive to the maximum point, which in our case is +-15V. The voltage divider divides it down to half, which is 7.5V. Depending on whether the output drives high or low, the voltag at the positive input is +-7.5V. The voltage at the capacitor on the negative input compares to this threshold and inverts the signal when it exceeds the treshold.
• To shape the spectrum of our oscillators we will use a lowpass filter. The simplest form of a lowpass filter is the passive lowpass filter.