Logic lever overview

We'll look at digital signals first.

Digital signals can only be in one of two possible states – on or off (high or low, true or false). They are binary and represent the way that modern computers work inside.

• Off (low/false) is typically represented by a voltage of 0V.
• On (high/true) is typically represented by a positive voltage, the magnitude of which depends on the particular system / protocol; 5V was traditionally the voltage used in most digital systems, however 3.3V has become more popular for newer systems. Some systems use lower voltages of 1.8V, 1.5V, 1.35V, 1.2V, etc – lower voltages use less power and so are more energy-efficient, however they are more susceptible to interference and attenuation, and so require more attention to hardware design.

Of course, the voltages in the system are unlikely to be exactly 0V and 5V, so there is some tolerance regarding what range of voltages represents on/high, and what range of voltages represents off/ low. Modern integrated circuits can consist of billions of tiny transistors, and the on /off thresholds depend on the type of transistors used:

https://www.labcenter.com/blog/sim-analogue-digital-signals/#header-3

https://e2e.ti.com/support/logic-group/logic/f/logic-forum/862744/faq-what-s-the-difference-between-ttl-and-5v-cmos-logic