This version was last updated around 2004. Many new terms (though very few basic concepts) have been introduced which are not covered. We don't do much in hardware these days (2011) so we have little incentive to keep it current. This stuff may be old but is still both highly relevant and absolutely fascinating.
With many thanks here for the original of this now much modified version. We would also suggest you look at this 6 volume series of books by Tony R Kuphaldt 'Lessons in Electric Circuits' published under the OpenBook initiative (means its free).
|AC||Alternating Current. In a time/voltage diagram, AC voltage represents a sine function (usually), or just any periodically alternating function. The mains voltage is AC voltage, for example.|
|Active high /
|Normally, signals are active high, which means a voltage level of 0V represents a logical 0 (LOW) and a voltage of above 5V represents a logical 1 (HIGH). If, for example, an IC pin is named "CS" (chip select), the chip is usually selected by pulling this line to HIGH (5V for TTL), and it gets deselected by pulling it to LOW (0V).|
|Ammeter||Device for measuring electric current. Usually part of a multi meter.|
|AND||Logical function which is TRUE if all inputs are TRUE.
A B | A AND B -----+------- 0 0 | 0 0 1 | 0 1 0 | 0 1 1 | 1
Examples: 7408: 4 AND gates with 2 inputs each 7409: 4 AND gates with 2 inputs each, open collector 4081: 4 CMOS AND gates with 2 inputs each
|BGA||Ball Grid Array. A type of chip package where the fixing method consists of a number of solder balls mounted under the chip and directly soldered onto a PCB.|
|Bread Board||Board made of pertinax or other insulating material for building prototype circuits. It contains a matrix of holes. There are also types with soldering pads around the holes, these cost more but are easier to work with.|
|Buffer||Same as driver.|
|Bus||The name for a set of lines/signals fulfilling a common function, for example, the address bus and the data bus. Examples include the PCI bus, H.100 and H.110 buses|
|Capacitance||Electrical entity which describes the amount of charge a capacitor can store. Unit: farad (F).|
|Capacitor||A capacitor is an electrical element which is capable of storing small amounts of electrical energy, just like an accumulator. The five most common capacitor types are:
Since a simple capacitor only consists of two plates facing each other, you can imagine that even two wires lying in parallel have a certain capacitance. When you charge a capacitor by applying voltage to it, it first behaves like a shortcut, then its resistance increases until no current flows through it anymore. This shortcut period is also present in parallel wires (e.g. acable), it drains lots of power from the chip the wires are connected to and the longer the cable, the higher its capacitance, the longer the shortcut period, the higher the current which the chip has to endure, and the shorter the chip's lifetime.
Dimensions and sizes for chips are defined by JEDEC.
The following types are some examples:
|CMOS||Complementary Metal Oxide Semiconductor. TTL uses bipolar transistors, while CMOS chips use uni-polar transistors (FETs) which are connected complementarily (one p-mos, one n-mos), thus consuming virtually no power and staying much cooler than appropriate TTL chips. Alas, CMOS chips are not suitable for very high frequencies: when the input level changes, the supply voltage pin and GROUND get quickly short-circuited. The higher the switch frequency, the higher the shortcut time. If you run CMOS chips at high frequencies, most of the switching time there is a shortcut, resulting in high power consumption and heat generation.
The switching thresholds are less than 30% (LOW) and greater than 70% (HIGH) of the supply voltage.
As opposed to the TTL series (74xx), CMOS family chips are not bound to 5V supply voltage. Vcc ranges from 3 to 18V (for the 4000 family). There are also TTL compatible CMOS families available, e.g. the widely used 74HCxx series (voltage range 4-6V), where HC stands for High speed Cmos.
|Composite video||Video signal which comprises of color and brightness information as well as horizontal and vertical synchronization information. Since the video chip's output signals are mixed into one signal (the composite video signal) and then must be split again in the monitor, losses occur and deteriorate the display quality, often resulting in color streaks. If possible, use the computer's Chroma/Luma output, which carries brightness and sync information on one line, but color information on another line, which eliminates the color streaking. The best result is achieved by using an RGB output.|
|Conductor||A material is called a conductor if electrons can move through it, in other words, if it allows flow of electrical current. How well current can flow through the conductor is determined by its resistance. If the resistance is very high, the material is called an insulator.|
|Connector||Generic term describing any method of connecting one or more wires. The following lists some of the most common types of connectors:
|Continuity||A cable (or other conducting material) has continuity when it has a low resistance, when it therefore constitutes a shortcut.|
|Continuity tester||Device for checking for continuity. It reacts to a resistance below ~100ohm, normally acoustically; some devices have a selectable threshold. Usually part of a multimeter.|
|Counter||Counters are elements counting the number of clock signals and outputting them as binary or decimal representation on the output pins. Examples:
4060: 14-step CMOS binary counter with internal oscillator circuit 7468: 2 asynchronous decimal counters
|Current||Electrical entity which is defined by the amount of charge flow in Coulomb per second. Unit:=Ampere (A). 1 A = 1 C / 1 sec. Symbol:=I In electrical equations|
|DC||Direct current. DC voltage is linear and constant, and either positive or negative. The same applies to direct current. See also AC.|
|DAC||Digital-Analog Converter. Converts a digital signal to its equivalent analog format, for example, when playing digital audio the digital signal passes through a DAC to the external speakers or headphones.|
element which lets current
flow in only one direction (forward direction). Current flows if a positive
voltage greater than the forward voltage is applied to the anode of the diode
(the other end is called cathode and is usually marked with a black ring on
the case), otherwise, the diode has a very high resistance. If the applied
voltage is below the avalanche / blocking voltage (which is always negative),
the diode breaks down and constitutes a shortcut.
The rarely used germanium diodes have a forward voltage of 0.3V, while the standard silicon diode has a forward voltage of 0.6V. (Graphic symbol)
|DRAM||Dynamic RAM. DRAM needs a continuous refresh (through the use of CAS and RAS signals), as the information in it is stored by very small capacitors.|
|Driver||Sometimes called a Buffer. A driver's output level follows the input level if it is a non-inverting type, and it implements a NOT function, if it is an inverting type. Drivers are employed for:
Examples: 7404: hex inverter (6 inverters) 7414: hex inverter with Schmitt trigger inputs 7405: hex inverter with O.C. outputs 7406: inverting driver with O.C. outputs (30V) 7416: inverting driver with O.C. outputs (15V) 7407: non-inverting driver with O.C. outputs (30V) 4069: inverting CMOS driver 4049: inverting CMOS driver, buffered 4050: CMOS driver
|ECL||Emitter-Coupled-Logic. Very fast logic family and used in some processor designs such as the AMD2900 range.|
|EEPROM||Electrically Erasable PROM.
In contrast to EPROMs, EEPROMs don't need exposure to UV light to be erased,
but can be erased electrically. A big advantage is that is accessed like an
SRAM. Write accesses perform an automatic clear before write and thus make
writing EEPROMs as easy as writing to SRAMs. Series designator: 28xx, where xx
is the number of K bits stored.
Serial EEPROMs are labeled 24Cxx (8bit) or 93Cxx (16bit).
Low voltage eproms (PLCC): 3.3V are labeled 27Vxx.
|Electron||To be supplied.|
|EPROM||Erasable PROM. EPROMs allow the contents to be erased by exposing its builtin window to UV light. After this process, all memory cells contain $ff and the EPROM can be written again.
Series designator: 27xx, where xx is the number of K bits stored.
|Ohm's Law. Additional equations.|
|EXOR (XOR)||Exclusive OR. Logical function which is TRUE, if and only if, exactly one input is TRUE. Frequently called XOR.
A B | A XOR B -----+------- 0 0 | 0 0 1 | 1 1 0 | 1 1 1 | 0
Examples: 7486 : 4 XOR gates with 2 inputs each 74136: 4 XOR gates with 2 inputs each, open collector 4070 : 4 CMOS XOR gates with 2 inputs each
|FET||Field Effect Transistor. As opposed to normal bipolar transistors, these uni-polar transistors have a negligible flow of current through their gate (bipolar: base), they consume virtually no power. NMOS-FETs and PMOS-FETs can be coupled to form CMOS circuits.|
|FLASH||An EEPROM which can be written (and erased) in whole banks or sectors. Typically comes un Uniform Sectored or Bootstrap Sectored designs.
Series designator: 28Fxxx (12 V prg. voltage), 29Fxxx (5 V prg. voltage), and 29LVxxx/29SLxxx (3 V and below), where xxx is the memory capacity: 010 - 1 Mbit, 020 - 2 Mbit, etc. If the FLASH supports 16 bit organization, xxx is: 100 - 1 Mbit, 200 - 2 Mbit, etc. Early FLASH (before 1998) had a limit on the number of erase cycles (typically 100,000) but most modern FLASH has essentially no erase limits.
|Flip-flop||This edge-triggered element has two stable states, which are toggled on
different events, depending on the type:
Examples: 7470 : JK flip-flop with 3 inputs each, preset and reset 74L71: RS master slave flip-flop with 3 inputs each, preset and reset 74171: 4 D flip-flops with clear input
|Float||An electronic signal is said to 'float' when its value is not defined under all conditions. Floating is generally a 'bad thing' since random effects (e.g. induction) could easily change the value with unexpected or unpleasant results. Signals that would otherwise 'float' are typically 'pulled-up'(High) or 'pulled-down'(Low) with a weak resistor such that they can be easily changed when driven.|
|Fuse||A device designed to break a circuit when too much voltage or current is applied. The idea being that its cheaper to replace a fuse than a device.
Domestic fuses: Histrically little glass tubes with a wire of defined maximum voltage and current which melts when its capacity is exceeded. There are two common formats: 5 x 20mm (German) and 6 x 30mm (American). Modern wiring typically uses circuit-breakers which can be reset rather than replaced.
|Gate||A gate is a circuit on a chip, which implements a logical function. A 7406, for example, contains 6 gates (non-inverting drivers).|
|IC||Generic Term. Integrated Circuit. A set of gates etched on a silicon wafer. As ICs are very sensitive, they are enclosed or packaged in a plastic or ceramic case/carrier, with their inputs and outputs connected to metal pins or balls. An IC in a package is commonly referred to as a CHIP. Chips are also called ICs!|
|Impedance||Expresed in Ohms is the vector sum of all opposition to the flow of current in a (typically AC) circuit which includes resistance, capacitance and inductance.|
|Inductance||Measures in Henries. The ability of a component to store energy in the form of a magnetic field.|
|Inductor||A passive device that stores electrical energy in the form of a magnetic field. Normally consists of a wire loop or coil. Inductors are typically used to smooth out voltage fluctuations in power supply circuits.|
|Insulator||A material which doesn't conduct electrical current. The opposite is a conductor.|
|Inverter||Gate inverting a logical signal, thus implementing a NOT function. For examples, see drivers.|
|Latch||A set of flip-flops with a common clock signal. In each cycle, they take the logical input signals over to their outputs. Usually used to form multiplex address busses. As opposed to flip-flops, latches are level-triggered.|
|LED||An LED (Light Emitting Diode) is a diode emitting light when operated in a forward direction. Since it is a diode, it has a nearly negligible resistance and MUST be operated with a series resistor.
The forward voltages depend on the type:
While normal LEDs consume about 20mA, high efficiency LEDs require only currents from 2-4mA (depending on type and color), which means that you can directly connect them to standard logical outputs (74LSxx or CMOS 4000 series) without the need for a driver. Nevertheless, you still need an appropriate series resistor.
Generic Resistor value calculation = Ohm's Law:
V = I * R rewritten as R = V / I
Where V = voltage drop over LED (typically Power Supply Voltage - Vf of LED) and I = drive current (typically If or Imax in milliamps).
The calculation may generate a non-standard resistor value so the next highest value in the series should be used (most resistors are rated as +-5% their nominal value).
|Logic Tester/Probe||Detects and indicates logic TTL (and/or) CMOS voltage levels. It usually contains a pulse memory (comprising a flip-flop) that memorizes pulses too short to be noticed otherwise.|
|Mains voltage||The voltage at the wall outlet.
Australia: 240V @ 50Hz UK : 230V @ 50Hz Germany : 230V / 400V @ 50Hz (formerly 220V / 380V) Japan : 100V @ 75Hz USA : 120V / 125V @ 60Hz Note that since 1989, the standard European voltage is 230V @ 50Hz
|Monoflop||Also known as one-shot multivibrator. Flip-flop
with only one stable state. It remains in the unstable state for a certain
time determined by capacitors.
Examples: 74121: Monoflop with Schmitt trigger input 74221: 2 monoflops with Schmitt trigger input and reset 74122: Retriggerable monoflop with reset 74123: 2 retriggerable monoflops with reset
|MOS||Metal Oxide Semiconductor.|
|Multi-meter||An all-in-one measuring device. It combines a volt-meter, an amp-meter and an ohm-meter which usually also can act as continuity tester. Often it contains a transistor tester and measures capacities and inductivities (in a small range). There are both analog and digital types, the latter is the preferred choice.|
|NAND||Logical function which is TRUE if and only if not all of the inputs are
A B | A NAND B -----+--------- 0 0 | 1 0 1 | 1 1 0 | 1 1 1 | 0
Examples: 7400: 4 NAND gates with 2 inputs each 7401: 4 NAND gates with 2 inputs each, open collector 4012: 2 CMOS NAND gates with 4 inputs each 4093: 4 CMOS NAND gates with 2 inputs each and Schmitt trigger
|Negative logic||Negative logic means that the signals are active low.|
|NOR||Logical function which is TRUE if and only if all inputs are FALSE:
A B | A NOR B -----+--------- 0 0 | 1 0 1 | 0 1 0 | 0 1 1 | 0
Examples: 7402: 4 NOR gates with 2 inputs each 7423: 2 NOR gates with 4 inputs each and strobe 4001: 4 CMOS NOR gates with 2 inputs each 4002: 2 CMOS NOR gates with 4 inputs each
|NOT||Logical function which is TRUE if the input is FALSE:
A | NOT A ---+------- 0 | 1 1 | 0Inverters implement this function.
|NTSC||National Television Standard Code. Video encoding standard in the United States and in Japan. NTSC has 60 pictures/sec and 526 lines vertical resolution.|
|Ohm's Law||Defines the relationship between voltage (E) current (I) and Resistance (R) in a circuit. For DC circuits Ohms law is:
I = E / R (amps = volts / resistance in ohms) OR E = I x R (volts = amps x resistance in ohms)Additional equations.
|Ohmmeter||Device for measuring resistance. Usually part of a multi-meter.|
|Open collector||A possible output connection of a TTL circuit. The output is formed by a single transistor, which is not connected to the supply voltage, therefore an external connection to the supply voltage (via a pull-up resistor) is required. Multiple open collector outputs can be connected together, the outputs carrying a 0 signal will override all other outputs.|
|Oscilloscope||A test device which displays voltage curves graphically.|
|OR||Logical function which is TRUE if at least one input is TRUE:
A B | A OR B -----+------- 0 0 | 0 0 1 | 1 1 0 | 1 1 1 | 1
Examples: 7432 : 4 OR gates with 2 inputs each 74832: 6 OR drivers with 2 inputs each 4071 : 4 CMOS OR gates with 2 inputs each 4072 : 2 CMOS OR gates with 4 inputs each
|PAL||This acronym has two meanings:
|PCB||Printed Circuit Board. The circuit tracks or traces are etched photographically onto a media. PCBs may be single-sided (tracks on one side only), double-sided (both top and bottom surfaces are used) or multi-layer where tracks are placed on a number of separate layers which are then bonded together. Tracks are connected on multi-layer boards using VIAs (small holes). Holes are drilled in the board for thru-hole technology or solder pads provided for SMT or BGA devices. Components may be placed on the top or increasing on both the top and bottom of a PCB.|
|Photo diode||Diode which is controlled by light.|
|Photo transistor||Transistor which is controlled by light.|
|PLA||Programmable Logic Array. The same as a PAL, but with a programmable OR matrix|
|Positive logic||Positive logic means that the signals are active HIGH. Negative logic means that signals are active LOW (most commonly in RS232 circuits).|
|Potentiometer||A variable resistor the value of which is determined by the position of a slider or a knob.|
|PROM||Programmable ROM. This memory type can be written once, then it behaves like a ROM. Series designator: 25xx, where xx is the number of kbits stored.|
|Pull-ups (or pull-downs) have two primary purposes both of which are variations on a fundamental theme which is to prevent a short-circuit by adding a resistor in the path between Vcc and GND for a particular signal.
Configuration: Many ICs have pins which must be set to a HIGH or LOW to configure the chip. Unless the IC is defined to have an internal pull-up or pull-down you typically use a pull-up (the resistor is between the signal pin and Vcc) to set a HIGH (1) or a pull-down (the resistor is between the signal pin and GND) to set a LOW (0).
Floating Signals: If a signal is not being actively driven all the time it will float (i.e. take an arbitrary and maybe changing value). To prevent this it may be pulled-up (HIGH) or pulled-down (LOW) into a default state.
Pull-ups or pull-downs are usually weak (i.e high value resistors of 4.7K, 10K (most common) or 47K) since in the case of floating signals this allows the 'driven' level to overcome the resistance with a modest current. For minimum power loss especially in configuration functions use the highest value (47K). Since higher resistance values take longer to overcome than lower values if the signal needs to be stable very quickly you may need to go as low as 1K for the pull-up (pull-down).
|RAM||Random Access Memory. Information can be read and written in any order, the number of read or write accesses is not limited. RAM comes in different flavors: DRAM, SRAM, SDRAM, EDO-RAM, VRAM and many more.|
|Rectifier||Circuitry transforming AC into DC, usually consisting of 4 diodes (aka bridge rectifier).|
|Resistance||The resistance of a conductor (or an insulator) is how easily current can flow through it. Unit: ohm (capital omega) Symbol = R.|
|Resistor||Electrical element with a defined resistance. It is used as voltage divider, current limiter or for ensuring that signals do not float. For small through-hole resistors, their value is not printed on the case, but encoded with color rings.|
|Radio Frequency (RF)||Generic term defines equipment which works in the radio frequency range typically ? to ?.|
|RGB||Red-Green-Blue. These three colors are additively mixed in color TVs and monitors and so give a picture which ranges from black over all rainbow colors to white. The number of colors displayed depends on the technology: TTL or ECL supply digital signals and thus a limited color resolution, usually 4 bits, which results in 16 colors; analog signals, however, make the color resolution practically infinite, the number of colors only depends on the graphics card's memory and on its RAMDAC or VRAM.|
|RMS||Root Mean Square. The real peak value of an AC voltage, which is U * square root of 2, abbreviation Vrms. RMS is calculated as sqrt (value1^2 + value2^2 .../no. of samples).|
|ROM||Read Only Memory. Unlike RAM, this type of electronic memory can only be read. The ROM's content is determined during the manufacturing process (mask programming). Derivatives are PROM, EPROM, EEPROM, and Flash-EPROM.|
|SDRAM||Synchonous DRAM. Differs from conventional DRAM in that it internally gates (synchronises) all access using a single clock rather than separate column and row clocks (driven by CAS & RAS).|
|Schmitt trigger||A logical device that outputs 0 if the input voltage is below a given threshold voltage and 1 otherwise. Used to cleanup the edges of digital signals. Often comes with a built-in inverter.|
|Semiconductor||Pure semiconductor materials like silicon are insulators. But doping these materials with a very small amount of e.g. Bor makes them less insulating and, under certain circumstances, conduct electrical current. Common semiconductors are diodes and transistors, which are also etched into the silicon wafers of ICs.|
|SMD or SMT||Surface mounted device (Surface mounted technology). A chip packaging technique. SMD technique means soldering elements (which have specially designed, very short pins) directly onto pads on the PCB surface without drilling holes. Other packaging techiques are 'Thu-hole' and Ball Grid Array (BGA).|
|Solder||Solder is made of tin (Sn) and lead (Pb) and contains a rosin core, which makes the solder flow more easily.|
|Soldering iron||A tool for soldering electrical conducting connections.|
|SRAM||Static RAM. As opposed to DRAM, this type of memory doesn't need a continuous refresh, as the information in it is stored by flip-flops.|
|Thru-hole (THT)||A chip packaging technology and requires holes in the PCB through which component pins were inserted and soldered on the reverse side. Through-hole is still widely use for connectors and other components that also have a physical use since the through hole provides a mechanical achoring function (e.g. DB25, RJ45 etc). Surface mount versions of these components exist but almost always use one or more mechanical locating holes or pins. Aternate packaging technologies are Surface Mount (SMT/SMD) and Ball Grid Array (BGA).|
|Thyristor||Sometimes called a semiconductor controlled rectifier. It has 3 pins (anode, cathode and gate). When powered and Gate is ON (high) forward current only will flow from the anode to cathode (irrespective of state of the Gate) until it drops below a certain level (called the Holding Current). It can be used to rectify current.|
|Totem pole||A possible output connection of a TTL circuit. A totem pole consists of two transistors, which are driven complementary. Depending on the desired output, only one of the two transistors is conducting. If two totem pole outputs are connected, a shortcut occurs if they carry different digital signals (0/1 or 1/0).|
A transformer changes one AC voltage into another AC voltage. It consists of two coils (actually not separate coils, but windings) with a different number of turns, where one coil (transformer primary winding) encloses the other (transformer secondary winding). The current flowing through the transformer primary (the one where the input voltage is applied) invokes a magnetic field which in turn induces a voltage in the transformer secondary, the amount of which is determined by the ratio of the number of turns of the windings.
A transformer can have more than one secondary, resulting in more than one output voltage.
|Transistor||"Transfer Resistor". Invented in 1948 by John Bardeen and Walter Houser Brattain. In principle, this element is an electrically controllable
semiconductor resistor. It has three terminals C(ollector), E(mitter), and
B(ase). Basically, when there is no voltage applied to the base, the
transistor acts as an insulator
and blocks current flow between C and E.
It is used both as an amplifier and an electronic switch.
|Triac||Provides similar functionality to a thyristor but supports bi-directional current flow.|
|The output lines of tristate circuits can have three states: HIGH, LOW, and HIGH IMPEDANCE (HI-Z), where the latter is equivalent to not being connected.|
|TTL||Transistor-Transistor-Logic. The TTL family needs a supply voltage of
4.75V-5.25V, the switching threshold is less than 0.8V for LOW and greater
than 2.4V for HIGH.
Type Meaning typ. t [ns] Power[mW/G] ---------------------------------------------------------------- 74xx Standard 10 10 74ALSxx Advanced Low Power Schottky 4 1 74ASxx Advanced Schottky 1.5 20 74Fxx Fast Schottky 2 4 74Hxx High Power 6 20 74Lxx Low Power 30 1 74LSxx Low Power Schottky 9 20 74Sxx Schottky 5 20
* tpd = propagation delay time. Time for an output level change after the input level changed.
|Voltage||Electrical entity which is the cause for current flow. When talking about AC voltages, peak-to-peak voltage means - as the name suggests - the absolute amount of voltage between the upper and the lower bound; Abbreviation: Vcc. Unit: Volt (V).|
|Voltmeter||Device for measuring electrical voltage. Usually part of a multimeter.|
|VRAM||Video RAM. VRAM is dual-ported, so that you can read and write simultaneously, resulting in a much smaller access time. As the name suggests, VRAMs are employed as memory on graphic cards.|
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