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Project Notes

#021 Schmitt Inverter

Use an Arduino to demonstrate the basic operation of 74LS14 Hex Inverter with Schmitt Trigger Inputs chip, and plot the results with Processing.

Here’s a quick video of the circuit in action:

Schmitt Inverter


The circuit uses a digital output pin to drive one inverter unit of the 74LS14 chip. The input and output levels are read with analog input pins, and the values is echoed to the Arduino serial port for plotting.

All unused outputs on the 74LS14 are left open circuit. Unused inputs are grounded, as is recommended to avoid unstable operation.

LEAP#090 PlotNValues (a simple Processing sketch) reads the data from the serial port and plots the input and output value over time, with some coloration effects thrown in for good measure. In other words, we’re using Arduino and Processing as a basic oscilloscope! And it kind of works, mainly because the frequency is so low.

Here’s a sample trace. The lower trace is the signal input, and the upper trace is the output of the inverter.

processing trace

Compared with a simple BJT inverter, we see a much cleaner signal.


The Breadboard

The Schematic

The Build

Credits and References

Project Source on GitHub Project Gallery Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is just my personal collection of projects. Two main themes have emerged in recent years, sometimes combined:

  • electronics - usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting
  • scale modelling - I caught the bug after deciding to build a Harrier during covid to demonstrate an electronic jet engine simulation. Let the fun begin..
To be honest, I haven't quite figured out if these two interests belong in the same GitHub repo or not. But for now - they are all here!

Projects are often inspired by things found wild on the net, or ideas from the many great electronics and scale modelling podcasts and YouTube channels. Feel free to borrow liberally, and if you spot any issues do let me know (or send a PR!). See the individual projects for credits where due.