Schematic Diagrams Schematic diagrams are used to graphically represent the components and interconnections of electrical circuits. Electronic schematics consist of symbols that represent the individual electronic parts used in the circuit. These symbols are interconnected with lines that represent the actual electrical connections.

Preferred Schematic Diagrams Practices A well-drawn schematic makes it easy to understand how a circuit works and aids in troubleshooting; a poor schematic only creates confusion. In order to draw a good schematic, you should keep the following suggestions in mind.

General Principles Schematics should be unambiguous. Therefore, pin numbers, parts values, polarities, etc., should be clearly labeled to avoid confusion. don’t do

Rules Wires connecting are indicated by a heavy black dot; wires crossing, but not connecting, have no dot (don't use a little half-circular ``jog''; it went out in the 1950s). dodon’t

Rules (Cont.) Four wires must not connect at a point; i.e., wires must not cross and connect. don’t do Do Don’t

Rules (Cont.) Always use the same symbol for the same device; e.g., don't draw flip-flops in two different ways Wires and components are aligned horizontally or vertically, unless there's a good reason to do otherwise.

Rules (Cont.) Label pin numbers on the outside of a symbol, signal names on the inside. All parts should have values or types indicated; it's best to give all parts a label, too, e.g., R7 or IC3.

Hints Identify parts immediately adjacent to the symbol, forming a distinct group giving symbol, label, and type or value. do don’t

Hints (Cont.) Signals should flow left to right and in rows from top to bottom. Orient connectors and devices in accordance with the signal flow principle: –Orient connectors. Input connectors on the left and output connectors on the right. –Orient devices. Normal orientation is with inputs on the left and outputs on the right, positive power on top, and negative power or ground at the bottom.

Hints (Cont.) Always pointing grounds downward. do don’t

Hints (Cont.) Put positive supply voltages at the top of the page, negative at the bottom. Thus, npn transistors will usually have their emitter at the bottom, whereas pnp's will have their emitter topmost. dodon’t

Hints (Cont.) Tie leads together at a single power or ground object may improve the schematic layout. do don’t

Hints (Cont.) Use bus structures to relieve signal congestion for all data and address signals. Use labels to implicitly join separated wire segments together rather than routing the wires over great lengths.

Hints (Cont.) don’t do

Hints (Cont.) An awful schematic

Hints (Cont.) A good schematic