A design diagram refers to a particular kind of circuit diagram which utilizes standard electrical/electronic symbols rather than pictures to show how a circuit (or a part of it) works. Below is a standard 3-wire motor controller circuit using a standard momentary stop - start pushbutton channel working with a schematic diagram. (Momentary here means that the button/switch you trigger will return to its default location once you physically let go of it, typically by a spring that forces the button/switch to do this.)
Consider it this way; a circuit diagram is any sort of diagram which demonstrates the way the circuit functions where the most important objective is the proper wiring of elements and their connection to each other rather than physical location relative to each other or intending prototypes. However, in some uses classifying diagrams can be challenging so do this as general advice. I have discovered this is particularly true when working with much more complex circuits and electronic equipment. I'm going to work with a more straightforward but average industrial circuit because these circuit set ups are the exact same, but yet where it is possible to observe how each kind of diagram shows the purpose of the circuit in their own manners.
Right, less clutter? I have enough info in each these diagrams to know exactly what this circuit does and where to start looking for problems. Hope this helps. ( Note: do not confuse circuit or schematic diagrams together with wiring diagrams; wiring diagrams will usually demonstrate images of components such as the pictorial, and also the way the whole or portion of a circuit is wired. The distinction is that wiring diagrams usually put an emphasis on real physical location of necessary components relative to each other that essentially tell a layman exactly what to do concerning the wiring)
Pictorial design diagrams, or pictorial circuit diagrams are basically the exact identical thing with the same function, however they use pictures of components inside the circuit instead of symbols. Again, here is the exact same precise circuit (almost except a controller was inserted and they're using conductors L1 and L3 rather than L1 and L2.
Here's a specialized variant of a diagram. The most important point of this diagram is to demonstrate the logic (speaking to electric management ) of a circuit. This really is the one I mainly come across in my line of work, and it is extremely successful for troubleshooting issues or learning how a circuit functions. Some frequencies are so huge that many kinds of schematic diagrams have to be recorded in increments from book form (generally with coded numbers so information can be simpler found). Again, here's the same specific circuit because the first 2, however, looking at it in ladder shape.
Here is another schematic diagram showing the same circuit, components and connections and it appears different but they both fall into exactly the same category.