EFA:002 OLD – Simple Oscillator with 40106




  • Basic Components
  • 40106 [Hex Schmitt Trigger Inverter] – We use this to create oscillators for controlling LEDs and producing annoying sounds

Tools & Skills

RC Circuit

The first thing we are going to build today is an RC circuit (resistor-capacitor circuit). RC circuits are most commonly used to create various timers and filters. It is also how the flash on a camera works. They are also very useful for helping to understand how some of the most important electronic components – resistors and capacitors – work.

Part 1: Simple LED Circuit with a Switch

Firstly, let’s just create a simple circuit where an LED turns on when we press a button.

See the interactive simulation here

Part 2: RC Circuit

The next step would be to create an RC charging circuit. Here we just have a simple circuit with a resistor and a capacitor connected in series. The values of the resistor and the capacitor determine the time it takes for the capacitor to charge.

See the interactive simulation here

More information about RC circuits from Electronics Tutorials.

This circuit just charges the capacitor. I will demonstrate in class using the oscilloscope how the charging looks like.

Part 3: Fading the LED with an RC circuit

Now we should combine these two things together to visually see the effect of charging and discharging the capacitor. The fading in of the LED happens fairly quickly so you will not see a huge difference when turning it on, but you should see the LED clearly fading out when you release the button.

See a simulation of this circuit

Creating Oscillators with the 40106

There are many different ways to use the charging and discharging of capacitors to create oscillators, but we are going to use a simple inverter logic chip.

See the detailed tutorial from this page.

Click the image for an interactive simulation

Going Further

We will continue with this chip all week. Tomorrow we will add an audio amplifier to this circuit to hear how the waveform sounds like.

Some Alternative Chips

  • 555 – The 555 timer chip is also very popular for creating oscillators. It requires more parts and it’s a bit more complicated to build, but a very useful little chip to have in your toolkit.
  • 4093 – Quad 2-input Schmitt Trigger. It can be used to build oscillators in a very similar way to the 40106.