Castle is based around 3-bit binary digital signals:

A binary number is a number expressed in the base-2 numeral system or binary numeral system, a method of mathematical expression which uses only two symbols: typically "0" (zero) and "1" (one).
The base-2 numeral system is a positional notation with a radix of 2. Each digit is referred to as a bit, or binary digit. Because of its straightforward implementation in digital electronic circuitry using logic gates, the binary system is used by almost all modern computers and computer-based devices,...

Imagine 3-bit binary like an 8 layer cake. All combinations of 3 bits create 8 possible values. Ever seen NTSC color bars? If you send 3-bit binary into RGB, you get those colors.
All the inputs on the modules are comparators, so they can perform a 1-bit conversion of an analog signal:

The ADC module slices analog voltages up into 3-bit binary numbers:

In electronics, an analog-to-digital converter (ADC, A/D, or A-to-D) is a system that converts an analog signal, such as a sound picked up by a microphone or light entering a digital camera, into a digital signal. An ADC may also provide an isolated measurement such as an electronic device that converts an analog input voltage or current to a digital number representing the magnitude of the voltage or current. Typically the digital output is a two's complement binary number that is proportiona...

If you patch a triangle waveform into the ADC, you get a step pyramid waveform out!
The DAC module converts 3-bit binary numbers into analog voltages:

In electronics, a digital-to-analog converter (DAC, D/A, D2A, or D-to-A) is a system that converts a digital signal into an analog signal. An analog-to-digital converter (ADC) performs the reverse function.
There are several DAC architectures; the suitability of a DAC for a particular application is determined by figures of merit including: resolution, maximum sampling frequency and others. Digital-to-analog conversion can degrade a signal, so a DAC should be specified that has insignificant ...

There’s also a voltage controlled oscillator, these make horizontal or vertical bars in different sizes:

An electronic oscillator is an electronic circuit that produces a periodic, oscillating electronic signal, often a sine wave or a square wave or a triangle wave. Oscillators convert direct current (DC) from a power supply to an alternating current (AC) signal. They are widely used in many electronic devices ranging from simplest clock generators to digital instruments (like calculators) and complex computers and peripherals etc. Common examples of signals generated by oscillators i Oscillators...

You combine the binary outputs to make complex patterns with these:

A logic gate is an idealized model of computation or physical electronic device implementing a Boolean function, a logical operation performed on one or more binary inputs that produces a single binary output. Depending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and unlimited fan-out, or it may refer to a non-ideal physical device (see Ideal and real op-amps for comparison).
Logic gates are primarily implemented using diodes or transistors...

It gets freakin crazy when you start messing with the counter, shift registers, and flip flops, which allow you to program memory states and reveal the true digital nature of everything:

In electronics, a flip-flop or latch is a circuit that has two stable states and can be used to store state information – a bistable multivibrator. The circuit can be made to change state by signals applied to one or more control inputs and will have one or two outputs. It is the basic storage element in sequential logic. Flip-flops and latches are fundamental building blocks of digital electronics systems used in computers, communications, and many other types of systems.
Flip-flops and latches...

In digital logic and computing, a counter is a device which stores (and sometimes displays) the number of times a particular event or process has occurred, often in relationship to a clock. The most common type is a sequential digital logic circuit with an input line called the clock and multiple output lines. The values on the output lines represent a number in the binary or BCD number system. Each pulse applied to the clock input increments or decrements the number in the counter.
A counte...

It follows LZX standards, for patching and interfacing video signals, and requires Cadet 1+Cadet 2 or Visual Cortex as core modules:

https://community.lzxindustries.net/t/the-lzx-patchable…/842

Read up a bit on video sync and how the raster works:

https://www.maximintegrated.com/en/app-notes/index.mvp/id/1184

Stay inspired and have a creative goal to challenge yourself with:

And learn some history:

The Color Graphics Adapter (CGA), originally also called the Color/Graphics Adapter or IBM Color/Graphics Monitor Adapter, introduced in 1981, was IBM's first color graphics card for the IBM PC and established a de facto computer display standard.
The original IBM CGA graphics card was built around the Motorola 6845 display controller, came with 16 kilobytes of video memory built in, and featured several graphics and text modes. The highest display resolution of any mode was 640×200, and the hig...

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