How do schematics work

Read circuit / wiring diagram

Reading an electronic circuit or a circuit diagram is not that easy for a beginner in electronics. Some basic knowledge, years of experience, correct combinations and a healthy electronics technician's mind are the things that the electronics technician uses to read a circuit diagram.
The description that follows is not a firmly defined set of rules, but is intended to make it easier for beginners to read circuits and circuit diagrams, i.e. to make it easier for them to recognize components and component values. However, this does not mean that the following description is unconditionally suitable for the electronics novice. In electronics it is necessary to master certain basics. Without it you will not be able to read a circuit.
It is therefore advisable to deal with the basics of electronics, electronic components and circuit technology beforehand and to have roughly understood them.

You don't get the necessary basic knowledge about electronic circuits by reading books, but by experimenting on real circuits yourself. This works best with the electronics learning packages from Franzis. There's something for everyone.

Detect voltage source or power supply

The voltage source can be recognized in the circuit diagram by a long bar for plus and a short bar for minus.

Usually each circuit has a power supply. Logical, otherwise it wouldn't work. Since you do not need a special power supply for each circuit, the level of the operating voltage is usually specified. Often, however, the operating, input and output voltage can only be identified by a U or a V. Most often they carry a sign and an index with them. A plus (+) sign indicates a positive operating voltage. A minus (-) indicates a negative operating voltage. In the case of operating voltage connections, the operating voltage is usually the same as a voltage value in volts.
Operating voltage, total voltage and supply voltage are often used synonymously. The total voltage is often used in mathematical tasks involving series and parallel connections. However, the operating and supply voltage are the same.
Input and output voltages are usually marked in electronic circuits, but it is seldom stated what needs to be applied or what comes out. Here you have to understand how the circuit works or find a description.

Most of the voltage terms come from the English or American language area.

Operating voltageU / UBat / V
Operating voltage, positive+ UB. / V + / V ++ / VCC / VCC / VS +
Operating voltage, negative-UB. / V- / V- / VEE / VSS / VS-
Total tensionUtotal
Reference voltageUref / Vref
Input voltageUE. / Ue / VIN
Output voltageUA. / Ua / VOUT
Ground, groundGND or 0V

Earth, ground, ground and minus?

In electrical engineering and electronics, terms such as ground, earth, device earth and ground are often used and unfortunately also mixed up. Which term describes what?


The earth is the potential of the earth. Thus the grounding is a form of the ground (connection). The device earth is a synonym for ground and designates the reference potential of the device.


The ground is a reference potential. The mass can be earthed. But it doesn't have to be. The potential starts from the earth potential and can be offset from a correspondingly predetermined potential. So it doesn't have to be 0 volts. For example in the car, earth is difficult there.


Ground, GND for short, is just the English name for ground. Sometimes it is used in slang for "earth" or as a synonym for "mass". But actually it means "earth". So a definite earth potential.


Minus means negative supply voltage and has nothing to do with GND or ground. It only happens sometimes that the negative supply voltage (minus) is connected to ground. But it can also be that plus is on mass.

Recognize components in a circuit

Electronic components can be recognized in the circuit diagram by the symbol. Due to different standards around the world, the representation of the components is not always uniform. Sometimes the differences are bigger, sometimes smaller. The most important electronic components that can appear in any circuit are shown in the table below.

Identification of components in circuits

In addition to the symbols, electronic components can also be identified by their identification. Since a component usually appears several times in a circuit, a number or an index is appended to the letter. This makes it easier to define a certain component when it is mentioned in a parts list or description.
Because some electronics technicians cannot remember the assignment of the identification (letters) to the component, a proliferation of identifications has established itself, which sometimes makes it difficult to clearly identify components.
The following table documents the characters according to the old and new standards and also takes into account invalid characters that are often found in unprofessionally created circuits.

new normold norminvalid
resistanceOhm (Ω)R.R.-
capacitorFarad (F)C.C.-
Kitchen sinkHenry (H)R.L.Sp, ...
diode-R.V.D, Q, ...
transistor-KV.T, Q, Trs

Some electronics technicians have difficulties with the component labels and do without them entirely. Instead, he writes the component values ​​directly to the component. Basically a good idea. This is definitely a practicable solution in small circuits. But not in larger circuits. Even an almost professionally created circuit diagram should always have component identifications. Older circuit diagrams are still marked according to the old standard. New circuit diagrams according to the new standard.

Read component values

Occasionally it happens that component values ​​are to be read in circuit diagrams instead of component identifiers. This saves the creator of the circuit diagram having to keep a parts list.
If there is not enough space, there are abbreviations in circuit diagrams. For example 10k, 47n or something similar. The creator of the circuit diagram assumes that the reader correctly interprets the abbreviated component value based on the component symbol. This means that if you want to interpret the abbreviated component values, then you have to take into account the type of component to which these values ​​refer.
So there is a high probability that 10k is associated with a resistor. 10k means 10 kOhm or 10,000 ohms. You save the ohm or Greek omega. The small k indicates that the numerical value must be multiplied by 1,000.
47n is typically assigned to a capacitor whose capacitance is 47 nF. Here, too, the unit F for Farad was dispensed with.
Electronics technicians usually know the abbreviations. In any case, it is important to know the associated component.

Sometimes other strange abbreviations are used as well. For example, a resistor says 4k7. Here the letter k is simply misused as a comma. Accordingly, it is a resistor with 4.7 kOhm or 4700 Ohm. The same procedure is used for capacitors and coils.

For example, another strange abbreviation for a resistor is 202. It is a 2 kOhm resistor. The system behind the designation is simple: The last digit describes the number of zeros (2 pieces) that are added after the first two digits. This gives the resistance value in ohms. That is 2000 ohms, or 2 kOhms.

Alphanumeric marking of resistors
Resistance value0.22 Ω2.2 Ω22 Ω220 Ω0.22 kΩ2.2 kΩ22 kΩ220 kΩ0.22 MΩ2.2 MΩ22 MΩ220 MΩ

Because the "Omega" for ohms does not appear in every character set, a simple "E" was previously used to replace the ohm as a unit. The notation was then 5E6 for 5.6 ohms. Whereby the E must not be confused with the exponent. "5 to the 6th" would be wrong.

Alphanumeric identification of coils
Inductance0.33 pH3.3 pH33 pH330 pH0.33 nH3.3 nH33 nH330 nH0.33 µH3.3 µH33 µH330 µH0.33 mH
Alternative labeling--33331331332333334334335---
Alphanumeric marking of capacitors
capacity0.47 pF4.7 pF47 pF470 pF0.47 nF4.7 nF47 nF470 nF0.47 µF4.7 µF47 µF470 µF0.47 mF4.7 mF47 mF
Alternative labeling--47471471472473474474475-----

Note: Sometimes you will find a unit like "uH" or "uF", which means "µH" or "µF". Because the letter "µ" cannot be found in every character set, it is permissible according to DIN to write a "u" instead of "µ" if the output device cannot output a "µ". In the computer sector in particular, you often get problems with special characters.

Why do you use such complicated abbreviations?

The abbreviations probably come from the era of stamps and typewriters. To make matters worse, the printing in the production machines was very imprecise. In the international arena, a period is often used instead of the comma. Such a printed fly shit is practically invisible. In order to exclude an illegibly printed comma or period as a source of error, it is best to leave it out right away. Basically, a minimal number of characters improves readability significantly. Even if it then becomes illegible again for the layman.

Housing for ICs and way of counting the connections

The counting method is always the same. From the notch you count counter-clockwise from 1, 2, 3, 4, etc. and then on the opposite side again from bottom to top. In the case of an 8-pin housing, connections 1 and 8 are opposite one another. For a 14-pin housing 1 and 14.And for a 16-pin housing, connections 1 and 16.

Recognize the function of circuit parts

In order to be able to recognize and understand the function of a circuit or a circuit part, one has to be familiar with the basic circuits of electronics and with the practical applications of components. Only when these requirements are met is it possible to read the function of a circuit.

There are also components whose function cannot be recognized immediately, but which are very important because they counteract certain electronic effects. Resistors, capacitors and diodes in particular sometimes take on functions that can only be recognized after practical application. Even experienced electronics technicians do not look at every component to see what purpose it fulfills.

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