Many ways to Blink a LED

Blinking a LED is the electronics equivalent of the famous “Hello World!”. Therefore it has a very special meaning, and it is also the basis of “clocks” which are very imprtant in digital electronics.

Let’s therefore find many creative ways to achieve that. Like using multiple languages, but here by using multiple electronics components and circuits.

Basics of operations

There’s 2 basic electronics components that allow for a response that varies in time:

• Capacitors
• Inductors

So, every Blink almost always comes down to using one of those 2 components. Yet, capacitors are much more using in reality¹, as they have a voltage response whereas inductors have a current response.

Storing current being much less practical than storing voltage, as current produces heat & interferences. Like storing kinetic energy with a flywheel² is more cumbersome than storing static energy with a spring.

This means that Blink usually always comes down to charging and discharging a capacitor.

Circuits

Note that there can be many variations of an original design. I’m leveraging the awesome interactive simulation from Falstad to illustrate my circuits.

Classic Circuits

Astable with 2 NPN

The oscillator circuit that usually everyone encounter at first is the famous “astable NPN” with its perfect symmetry of 2 NPN & 2 capacitors.

It actually starts to oscillate only because it is in instable equilibrium, and each component is not identical, even if having the same value, due to the manufacturing error margin.

Classic NE555

The most classic way of doing it would be to leverage the venerable NE555 in its “datasheet” astable configuration.

Classic with 3 NOT gates

This is also the classic that is the most often used in CMOS technology. It uses 3 NOT gates, but is always oscillating, and the period and cycle duty doesn’t depend on the voltage.

Classic with 2 NOT gates

A variation of the previous one. Only using 2 NOT gates, but not always oscillating.

Classic with a Schmitt Inverter

The simplest way to do an astable is to go for the Schmitt trigger version.

Variations

Now, as we can have variations of the individual components, we can also create new circuits out of it. But that will be another post.

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1. Some inductors based oscillator do exist, but are rather seldom. ↩

2. The comparison is rather accurate. In electronics, inductors have exactly the same usage as flywheels: avoiding current variations, not storing current. Springs on the other hand, are very good as energy restitution when needed. ↩