Read Schematics
Schematics are the maps that provide guidance on the functioning, assembly and service of an electronic circuit. Without a schematic, only an undocumented mass of components and wires would be presented to the user or service technician. A schematic allows the user or service technician to understand the circuit function and become familiar with how the desired effect of the electronic circuit is achieved. Use these tips to learn how to read schematics.
Steps
- Read schematics in the pattern that you would read text. With rare exceptions, schematics should be read left to right and top to bottom. The signal being generated or used by the circuit will flow in this direction. The user can follow the same path that the signal uses to understand what the signal does or how it is being modified.
- Understand the electronic language. There will be a variety of schematic symbols on the schematic that represent real world devices and wires. A basic understanding of these symbols is required to read a schematic. Lists of the symbols are readily available on the Internet.
- Understand ground. Ground is represented by either a triangle pointing down or a set of parallel lines that become shorter as they appear below each other, in effect representing the inner area of the triangle pointing down. Ground is a common reference point that schematics use to show the overall unity of the various functions of the circuit. It does not refer to the actual ground of the earth.
- Learn that a line represents a wire. Wires are used to connect the devices together. All points along the wire are identical and connected. Wires may cross each other on a schematic, but that does not necessarily mean that they connect. If they do not connect, one will be shown looping around the other in a semicircle. If they do connect, they will cross and a dot will be seen at the point where the lines cross.
- Learn that a resistor is represented by a zigzag shape. Resistors act to impede the flow of the circuit to an extent determined by the resistance value used. They are used to scale and shape the signal.
- Understand Ohm's Law. The voltage drop across a resistor is equal to the current flowing through it times the value of the resistor (V=IR). This allows the classic use of resistor to divide down a voltage. If a voltage source is applied to two consecutive resistors of the same value, the voltage created at the point between the two resistors will be half of the original voltage applied.
- Learn that capacitors are represented by two parallel lines. Capacitors are used to condition rapidly changing signals, as opposed to the static or slower changing signals that are conditioned by resistors. The traditional use of capacitors in modern circuits is to draw noise, which is inherently a rapidly changing signal, away from the signal of interest and drain it away to ground.
- Understand the non standard symbols. The non standard symbols will be of a geometric shape, usually a rectangle, with a device indicator number in or beside the shape. The indicator number should be Uxx. Wherever a wire contacts the device, there will be a number indicated at the connection point. This number is the pin number of the device.
- Find the correlation to all real parts. Refer to the bill of materials for the circuit to find the values of capacitors and resistors, and the manufacturers and manufacturer's part numbers of the active devices.
- Determine the circuit tasks performed by the active devices. To determine the circuit tasks, acquire and read the manufacturer's data sheet for each individual device.
- Evaluate what the circuit does. Based on the schematic, decide what parts of the circuit are performing what functions. This will help you determine the performance function of the entire circuit.
Tips
- Some capacitors are polarized. They will have a plus symbol on one side of the body shape. This means that the physical capacitor is to be installed a certain way. It does not affect circuit performance.
- Signals can exist in many parts of the circuit simultaneously. Do not assume that a signal starts in only one place and goes to only one place. No matter have many places a wire connects a signal to, the signal exists simultaneously in all of those places.
Related Articles
Sources and Citations
- www.learn-c.com/schemat.htm
