Electrical Engineering Crossword (Issue 280)

The answers to Circuit Cellar’s November electronics engineering crossword puzzle are now available.

280-crossword-key

Across

2.    DOPPLERLIMIT—Temperature restrictions for laser cooling techniques [two words]
4.    PINKNOISE—This signal sees the world through rose-colored glasses [two words]
5.    BOLTZMANNCONSTANT—k or kB [two words]
7.    XORGATE—A half adder is made of an AND gate and one of these [two words]
14.    NEPER—Symbolized by “Np”
15.    GOTOPAIR—Two tunnel diodes used in high-speed gate circuits [two words]
17.    YAGI—Unidirectional antenna
18.    PHOSPHOR—Used as a light source in a cathode ray tube
19.    KERREFFECT—All materials show this, but certain liquids display it more strongly than others [two words]

Down

1.    WEINBRIDGEOSCILLATOR—This type generates sine waves [three words]
3.    INTEGRATEDINJECTIONLOGIC—These digital circuits are built with several collector BJTs [three words]
6.    CARBONNANOTUBES—Their electronic properties can be metallic or semiconducting [two words]
8.    GILBERTCIRCUIT—Uses diodes and transistors’ logarithmic properties to compensates for nonlinearities and instabilities [two words]
9.    ADDRESSINGMODE—Can be implied by the instruction’s function [two words]
10.    SINADRATIO—Used to measure a signal’s standards
11.    FLATPACK—Semiconductor network sealed in a thin rectangular package
12.    SPEECHCLIPPING—Process that limits peak signals [two words]
13.    COMPANDOR—Condenses or enlarges an electric signal’s dynamic range
15.    GLASS—Device under development by search engine giant
16.    LILLIPUTIAN—A very small robot

 

Electrical Engineering Crossword (Issue 279)

The answers to Circuit Cellar’s October electronics engineering crossword puzzle are now available.

279-crossword-key

Across

1.    ERASABLE—The second “E” in EEPROM
4.    NYCRESISTOR—Brooklyn, NY-based open-community workspace [two words]
5.    WHITEHAT—A hacker with ethics may don one of these [two words]
6.    WIMAX—aka, IEEE 802.16
8.    STRUCTUREDQUERY—A type of data-management language [two words]
9.    PACKETSWITCHING—Data grouping method [two words]
11.    VOLTOHMMETER—Capable of measuring  voltage, current, and resistance [three words]
12.    ELUA—It’s free, open source, and embedded
13.    BUCK—A switched-mode power supply converter
14.    GOODPUT—This can be calculated by dividing a transmitted file’s size by the amount of time it takes to transfer the file
16.    GRAYCODE—One bit makes a difference [two words]
17.    UBUNTU—Linux-based OS
18.    WEARLEVELING—When applied to a flash memory, this technique can level out the amount of writes to any given memory block across the entire memory chip [two words]
19.    MOODLE—E-learning software developed by Australian computer scientist Martin Dougiamas
20.    CROSSEDFIELD—This type of microwave amplifier can also be used as an oscillator [two words]

Down

2.    LONGTERMEVOLUTION—Wireless communication standard [three words]
3.    CHEMILUMINESCENCE—A chemical reaction that creates a light emission
7.    BAXANDALL—A negative-feedback circuit used in high-quality audio amplifiers
10.    MICROKERNEL—µK
15.    PAUSEUS—BASIC command that creates a microsecond-based delay

 

Solar Cells Explained (EE Tip #104)

All solar cells are made from at least two different materials, often in the form of two thin, adjacent layers. One of the materials must act as an electron donor under illumination, while the other material must act as an electron acceptor. If there is some sort of electron barrier between the two materials, the result is an electrical potential. If each of these materials is now provided with an electrode made from an electrically conductive material and the two electrodes are connected to an external load, the electrons will follow this path.

Source: Jens Nickels, Elektor, 070798-I, 6/2009

Source: Jens Nickels, Elektor, 070798-I, 6/2009

The most commonly used solar cells are made from thin wafers of polycrystalline silicon (polycrystalline cells have a typical “frosty” appearance after sawing and polishing). The silicon is very pure, but it contains an extremely small amount of boron as a dopant (an intentionally introduced impurity), and it has a thin surface layer doped with phosphorus. This creates a PN junction in the cell, exactly the same as in a diode. When the cell is exposed to light, electrons are released and holes (positive charge carriers) are generated. The holes can recombine with the electrons. The charge carriers are kept apart by the electrical field of the PN junction, which partially prevents the direct recombination of electrons and holes.

The electrical potential between the electrodes on the top and bottom of the cell is approximately 0.6 V. The maximum current (short-circuit current) is proportional to the surface area of the cell, the impinging light energy, and the efficiency. Higher voltages and currents are obtained by connecting cells in series to form strings and connecting these strings of cells in parallel to form modules.

The maximum efficiency achieved by polycrystalline cells is 17%, while monocrystalline cells can achieve up to 22%, although the overall efficiency is lower if the total module area is taken into account. On a sunny day in central Europe, the available solar energy is approximately 1000 W/m2, and around 150 W/m2 of this can be converted into electrical energy with currently available solar cells.

Source: Jens Nickels, Elektor, 070798-I, 6/2009

Source: Jens Nickels, Elektor, 070798-I, 6/2009

Cells made from selenium, gallium arsenide, or other compounds can achieve even higher efficiency, but they are more expensive and are only used in special applications, such as space travel. There are also other approaches that are aimed primarily at reducing costs instead of increasing efficiency. The objective of such approaches is to considerably reduce the amount of pure silicon that has to be used or eliminate its use entirely. One example is thin-film solar cells made from amorphous silicon, which have an efficiency of 8 to 10% and a good price/performance ratio. The silicon can be applied to a glass sheet or plastic film in the form of a thin layer. This thin-film technology is quite suitable for the production of robust, flexible modules, such as the examples described in this article.

Battery Charging

From an electrical viewpoint, an ideal solar cell consists of a pure current source in parallel with a diode (the outlined components in the accompanying schematic diagram). When the solar cell is illuminated, the typical U/I characteristic of the diode shifts downward (see the drawing, which also shows the opencircuit voltage UOC and the short-circuit current ISC). The panel supplies maximum power when the load corresponds to the points marked “MPP” (maximum power point) in the drawing. The power rating of a cell or panel specified by the manufacturer usually refers to operation at the MPP with a light intensity of 100,000 lux and a temperature of 25°C. The power decreases by approximately 0.2 to 0.5 %/°C as the temperature increases.

A battery can be charged directly from a panel without any problems if the open-circuit voltage of the panel is higher than the nominal voltage of the battery. No voltage divider is necessary, even if the battery voltage is only 3 V and the nominal voltage of the solar panel is 12 V. This is because a solar cell always acts as a current source instead of a voltage source.

If the battery is connected directly to the solar panel, a small leakage current will flow through the solar panel when it is not illuminated. The can be prevented by adding a blocking diode to the circuit (see the schematic). Many portable solar modules have a built-in blocking diode (check the manufacturer’s specifications).

This simple arrangement is adequate if the maximum current from the solar panel is less than the maximum allowable overcharging current of the battery. NiMH cells can be overcharged for up to 100 hours if the charging current (in A) is less than one-tenth of their rated capacity in Ah. This means that a panel with a rated current of 2 A can be connected directly to a 20-Ah battery without any problems. However, under these conditions the battery must be fully discharged by a load from time to time.

Practical Matters

When positioning a solar panel, you should ensure that no part of the panel is in the shade, as otherwise the voltage will decrease markedly, with a good chance that no current will flow into the connected battery.

Most modules have integrated bypass diodes connected in reverse parallel with the solar cells. These diodes prevent reverse polarization of any cells that are not exposed to sunlight, so the current from the other cells flows through the diodes, which can cause overheating and damage to the cells. To reduce costs, it is common practice to fit only one diode to a group of cells instead of providing a separate diode for each cell.

—Jens Nickels, Elektor, 070798-I, 6/2009

Electrical Engineering Crossword (Issue 278)

The answers to Circuit Cellar’s September electronics engineering crossword puzzle are now available.

ACROSS

4.    ADIABATIC—Heat is neither gained nor lost
5.    DISCRETECIRCUIT—Made of resistors and transistors; not integrated [two words]
8.    FULLDUPLEX—Two-way communication [two words]
10.    KERMIT—Muppet-inspired protocol
12.    DEBIAN—Unix-like OS
14.    CHIRP—Conveys information
16.    FORTRAN—Others like it include BASIC and Pascal
18.    NANOKERNEL—Contains a minute amount of code capable of executing in the hardware’s privileged mode
19.    RHEOSTAT—Current regulator

DOWN

1.    BIPOLARJUNCTION—There are two types: NPN and PNP [two words]
2.    ECBBUS—1970s communication system for Zilog and Intel microprocessors [two words]
3.    VISUALSERVOING—Used to control a robot’s motions [two words]
4.    ATTOSECOND—10-18 of a second
6.    NICKELCADMIUM—This small, light, high-power type is commonly used in hand-held devices [two words]
7.    DEFCON—Place where hackers annually assemble
9.    PIGGYBACKING—Bi-directional data transmission
11.    GRASSHOPPER—Programming language for rhinos
13.    FLOSSMANUALS—Netherlands-based foundation that provides information about and access to free software [two words]
15.    RASPBERRYPI—An inexpensive SBC [two words]
17.    LIDAR—Laser-based measurement technique

 

Electrical Engineering Crossword (Issue 277)

The answers to Circuit Cellar’s August electronics engineering crossword puzzle are now available.

ACROSS

6.    ALGORITHM—Search engines use them to produce real-time results
9.    LOSSYCOMPRESSION—Condenses data by getting rid of some of it [two words]
11.    YOTTABYTE—Approximately 1,024 bytes
14.    PETAFLOP—Measures an FPU’s performance
15.    JQUERY—JavaScript library popularity contest winner
17.    THICKCLIENT—Able to function without a central server [two words]
18.    NYBBLE—4 bits
19.    DEGAUSSING—Gets rid of magnetism
20.    SPINTRONICS—aka, magnetoelectronics

DOWN

1.    YANG—Co-founded a multinational Internet company in 1994
2.    MICROSOFT—Originally created and sold BASIC computer programs for the Altair 8800 microcomputer
3.    CHARACTERLARGEOBJECT—Used to store large amounts of text [three words]
4.    ACGENERATOR—Changes mechanical energy into electrical energy [two words]
5.    DROPPER—Installs malicious code onto computers
7.    TRINITRON—Sony Corp.’s CRT technology
8.    BEAMWIDTH—Commonly specified at –6 dB, –10 dB, and –20 dB
10.    OVERCLOCKING—Makes the time go by more quickly
12.    FERROMAGNETIC—e.g., iron, cobalt, and nickel
13.    BAUDOTCODE—An early digital communication method [two words]
16.    AUTODYNE—Invented in 1914 by electrical engineer Edwin Armstrong, who is also credited with creating FM radio transmission