Hello folks,

today I want to start with a topic that I had already longer in my mind and finally took hands on.

We want to simulate a simple LFO (or a normal oscillator, depending on the chosen dimensions) and for that we use the relative well-known tool LTSpice that thankfully also works on Linux machines thanks to using the non-emulator wine.

A simple tutorial how to start that is found here.

Simple, after installation in the shell we enter (or copy):

We start with a schmitt-inverter based oscillator, utilizing a 40106 IC with six schmitt-inverters

Its based ont the VCO cicuit schematic from erica synths, see as below

Below the schematic from the datasheet

For more details, see the datasheet below

Datasheet

The important piece here is the following use case as astable multivibrator

We add two antiparallel diodes to the circuit, allowing to usse different timings for pulse and pause..

Dont forget to set values for the schmitt-inverter, otherwise it will not behave like it should, but like an ideal component, so do a right click on the schmitt inverter and under value add this: Vhigh=9 Vt=4.45 Vh=.85 Trise=.1u Tfall=.1u

After implementing the circuit part by part we end up with simulation, for that we need to set some initial condition .ic, the whole spice command is as below

additionally we need to set the transition times and how long the simulation should go..

A finished version of the oscillator to download:

osc.asc

That allows us to run the simulator:

Next, we can modify the resistor values and note that they control the pulse-pause-ratio .

Dont forget that, in a real circuit, you need an op-amp designed as voltage follower or impedance converter, like sketched blue in the cicuit schematic in order to be able to encumber the output with the next stage. Last but not least we have an RC filter on the end, a first-order high-pass filter…​

Thats it for now, see you later in other articles.