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Feature article ELECTRONICS Inventors and their Inventions in 1837, which was powered by galvanic cells. He then built a full-sized train in 1842 called “Galvani”; it was around 5m long. Edward Davy electric relay 1806-1885 He worked on the electric telegraph during 1835-1838 and was considered a contributor equal to Cooke and Wheatstone by J.J. Fahie. In 1837, he invented the electric relay, or “electric renewer” as he called it, as part of his telegraph system. In 1838, he migrated to Australia. Duchenne de Boulogne electrophysiology 1806-1875 Experimented with electrical stimulation on parts of the human body and is considered a pioneer in electrophysiology. He first published his work, “De l’electrisation localisée...” in 1855. You can read that book in the original French at pemag.au/link/abn8 Alfred Lewis Vail improved on Morse Code 1807-1859 Was involved with Samuel Morse in commercialising telegraphy 1837-1844. He enhanced Morse Code by simplifying the alphabetic system, making it easier to decode, along with other physical improvements. Modern electronics rests on the fundamental principles discovered long ago by people like Christiaan Huygens, Luigi Galvani, Charles Coulomb, Alessandro Volta, André-Marie Ampère, Carl Friedrich Gauss and many others. We described their discoveries last month; here, we pick up the story in 1804. Part 2: by Dr David Maddison T his series of articles started last month and will likely run to around six parts. That’s because there are so many people who contributed to our understanding of electricity and electronics over the last few hundred years. The first part last month started in 624BCE, although there were only two entries before 1544, the birth year of William Gilbert. Gilbert essentially coined the term “electricity”. Other important people in the field of electricity mentioned include Benjamin Franklin, Luigi Galvani, Charles Coulomb, Alessandro Volta, John Dalton, Thomas Johann Seebeck, André-Marie Ampère, Carl Friedrich 54 Antonio Meucci telephony and dynamic microphone 1808-1889 According to some, he was the https://unsplash.com/photos/_kdTyfnUFAc Gauss, Hans Christian Ørsted, Georg Simon Ohm, Michael Faraday, Samuel Morse, Joseph Henry, Charles Wheatstone and Wilhelm Eduard Weber. As with the last article, the people will be presented in order of their year of birth, although that means that their discoveries won’t necessarily be listed in chronological order. The discoveries and inventions in this article date from the 1830s, a point at which electricity and magnetism were already fairly well understood, but what we would call electronics today was still a field in its infancy. Robert Davidson electric train 1804-1894 Built the first electric locomotive Fig.16: Pixii’s dynamo. This later version produces pulsating direct current using the commutator below the magnet. Source: https://w. wiki/78sZ Practical Electronics | February | 2025 The History of Electronics, part two inventor of telephony. His notes show he produced a device in 1856 that communicated voice via wires from his basement laboratory to his wife upstairs in their New York home. This included a type of dynamic microphone with a wire coil moving in response to sound within a magnetic field. From 1856 to 1870, he developed more than 30 types of phone apparatus. In 1860, he publicly demonstrated his “teletrofono” in New York. In 1870, he transmitted voice signals over more than 1.6km of wire. In 1871, he submitted a patent caveat to the US Patent Office. This document was essentially a notice of an intent to file a patent, but Meucci didn’t have the money to submit a patent application. Had he been able to, it might have stopped Alexander Graham Bell from receiving his telephone patent in 1876. The invention of electric light The story of the invention of electric light is far too long and complicated to fully cover here. We have included highlights, but if you want to know more, read “The Invention of the Electric Light” (236 pages) by B.J.G. van der Kooij, a free PDF download from pemag.au/link/abnh Hippolyte Pixii 1808-1835 hand-cranked dynamo (electrical generator) Invented a hand-cranked dynamo in 1832 based on Michael Faraday’s discovery of electromagnetic induction. It produced an alternating current when a horseshoe (permanent) magnet passed over two iron cores – see Fig.16. At the time, DC was the preferred means of current for experiments. Upon André-Marie Ampère’s suggestion, a commutator to reverse the current direction every half turn was later added to produce pulsating direct current. William George Armstrong hydroelectric power station 1810-1900 He built the first hydroelectric power station (Fig.17) in 1870. It was the Burnfoot Power House at Cragside Estate, Rothbury, England and used a Siemens dynamo. He was titled 1st Baron Armstrong. Alexander Bain electric clock and facsimile machine 1810-1877 Patented an electric clock in 1841 with John Barwise. Its pendulum was driven by electromagnetic pulses. It included a reference to an “earth battery” made of dissimilar metals, buried in the ground, as a power source. He also patented a telegraph in 1843 that printed messages, an early form of the facsimile machine. The image to be transmitted had to be Fig.17: the first hydroelectric power station, on a private estate in Rothbury, England. Source: https://w.wiki/78sa (CC-BY-SA-4.0). Practical Electronics | February | 2025 55 Feature article Controversy over the invention of the telephone You may notice many references in this article to various people who made telephone-­related inventions. The matter of who invented the telephone has been subject to considerable controversy, including the long-running court case in the USA from 1878 to 1901 involving A.G. Bell, Thomas Alva Edison, Elisha Gray, Emil Berliner, Amos Dolbear, J. W. McDonagh, G. B. Richmond, W. L. Voelker, J. H. Irwin and Francis Blake Jr. Bell and the Bell Telephone Company eventually won that case, along with 600 other cases involving the invention of the telephone that went to trial. Another controversy involved Antonio Meucci. See https://w.wiki/78sh formed by metal pins arranged on a rotating cylinder, so it was not very practical. In 1846, he patented a printing telegraph that printed Morse Code on moving paper tape using chemical rather than mechanical means. He also devised a punched paper tape system for prerecorded messages that could be transmitted quickly. It could send 325 words per minute, compared to the Morse system at only 40 words per minute. Samuel Morse claimed patent infringement, and the system was not widely used. causing the emission of light by fluorescence – see Fig.19. The technology was a predecessor to neon lighting. Frederick Hale Holmes 1812-1875 continuous current electro generators Ernst Werner von Siemens Developed generators to power electric arc lighting in 1853. In 1856, he patented a magneto to power lighthouse arc lamps – see Fig.18. Invented the “pointer telegraph”, in which a message was received by needles pointing at letters rather than Morse Code. In 1847, he established Telegraphen-Bauanstalt von Siemens & Halske to produce it (see the video at https://youtu.be/v8DZuT5c2CI). Siemens AG is still an innovative company today. In 1874, he received US Patent Heinrich Geißler 1814-1879 Geissler tube – early form of neon lighting Invented the Geissler tube in 1857, a partially evacuated glass tube filled with various gases with a high voltage applied between two electrodes, Warren De la Rue incandescent light globe 1815-1889 He enclosed a platinum wire in an evacuated glass tube in 1840, creating an early incandescent light globe. Giovanni Caselli fax machine 1815-1891 Invented the first practical fax machine in 1861, called the “pantelegraph” (“pan” meaning all in Greek). You can see a photo of it at: https://w. wiki/78ro 1816-1892 pointer telegraph, speakers, electric lifts etc 149,797 for a “Magneto-Electric Apparatus” for “obtaining the mechanical movement of an electrical coil from electrical currents transmitted through it”. Although not intended as a loudspeaker, that is what became of the invention. Alexander Bell was granted a patent for the telephone in 1876, which incorporated a moving-iron type loudspeaker. Subsequently, Siemens received German patent 2355 in 1877 for an improved speaker design with a moving coil transducer, a diaphragm as a sound radiator and a trumpet form as a cone. This was adapted by A. L. Thuras and E. C. Wente for use by the Bell System as a loudspeaker. In 1880, Siemens built the world’s first electric lift. He was the first to use gutta-percha latex to insulate telegraph cables, making the 1866 transatlantic telegraph cable possible. He also invented a practical dynamo and an electric railway. He also developed a process for galvanoplasty, plastics with gold or silver plating. The unit of conductivity, the siemens (S), is named after him. Scott de Martinville 1817-1879 phono-autograph Invented the earliest known device to record audio waveforms in 1857, the phonautograph (see Fig.20). However, these waveforms could not be played back. In 2008, some waveform images from 1860 were digitised and converted back into sound, thus becoming the earliest known intelligible recording Above: Ernst Werner von Siemens also invented the trolleybus, usually powered from overhead lines. Source: https://w.wiki/7Arv Fig.18: Frederick Hale Holmes’ generator from Souter Lighthouse. Source: https://w.wiki/7A2K (CC-BYSA-4.0). 56 Fig.19: a Geissler tube in the form of a piece of modern art. Source: https://w. wiki/78sf (CC-BY-2.0). Fig.20 (right): a phonautograph visual recording, c.1859. Source: https://w.wiki/78sb Practical Electronics | February | 2025 The History of Electronics, part two of a human voice. They were made 28 years before Thomas Edison’s wax cylinder phonograph recordings. James Prescott Joule 1818-1889 magnetostriction and Joule heating An English physicist in the field of thermodynamics who established the concept of energy conservation, showing that heat, electricity and mechanical work were interchangeable. He discovered the relationship between current, resistance, and heat generation, which led to Joule’s Law. The unit of energy, the joule (J), is named after him. He also did work in the area of magnetostriction. In 1843, he discovered the relationship between the heat dissipated by a resistor and the current through it. Resistance heating due to a current flow became known as Joule heating. Léon Foucault 1819-1868 eddy currents Credited with the discovery of eddy currents or “Foucault currents” in 1855, although these were first observed by Dominique François Jean Arago (see his entry last month). Charles S. Bradley 1819-1888 three-phase generator Built the first three-phase generator in the USA in 1887. Moses Gerrish Farmer 1820-1893 duplex telegraphy, electric locomotives, bulbs He investigated telluric currents, low-­f requency currents that travel through the Earth or sea of natural or artificial origin. In 1847, he demonstrated an electric locomotive that pulled two passengers on tracks, powered by a nitric acid battery. Along with William F. Channing in 1849, he demonstrated an improved electric fire alarm system in 1857. In 1852, he made repeaters for a telegraph system and, in 1853, patented a method to transmit four messages on one telegraph line simultaneously. In 1859, he co-created the self-­exciting dynamo. He invented a current regulator for his electric lamps in 1859. The “Wallace-­Farmer 8 horsepower” (6kW) dynamo was used by Thomas Edison in early lighting demonstrations. He made an incandescent light globe, also in 1859, using a platinum filament and lit his house with them in July 1859, the first house to be lit by electric lighting (not Joseph Swan’s, as usually claimed). John Stephen Woolrich 1820-1850 Woolrich Electrical Generator He built the Woolrich Electrical Generator in 1844, the first generator used for an industrial process, commercial electroplating (see Fig.21). The voltage and current ratings are unknown. Edmond Becquerel 1820-1891 photo-voltaic cell He produced the first photovoltaic cell in 1839 (see Fig.22). When light was directed onto the device, voltage and current were produced. The photovoltaic effect is now known as the Becquerel effect. John Wellington Starr 1822-1846 carbon & platinum filament incandescent globes Filed patents in 1845 for two types of incandescent light globe, one based on a carbon filament and the other on a platinum filament. They were never commercialised. Nevertheless, the patent is considered the first important one on the road to a commercial electric light globe. There is quite an extensive story to John Starr and many uncertainties; see pemag.au/link/abn9 Hermann von Helmholtz 1821-1894 Fig.22: the first photovoltaic device from Edmond Becquerel. Source: www.pveducation.org/pvcdrom/ manufacturing-si-cells/firstphotovoltaic-devices nets arranged to provide a region with a close-to-uniform magnetic field. A Helmholtz resonator is an enclosed volume with a neck that resonates at a specific frequency. They are incorporated in some car exhaust systems to eliminate noise at certain frequencies, and this phenomenon is also the cause of ‘wind throb’ in a car with open windows at certain speeds. See the video titled “How to build a Helmholtz Resonator DIY” at https:// youtu.be/JUsyeBkNVEI Lord Kelvin 1824-1907 bandwidth, mirror galvanometer etc Also known as William Thomson, developed and patented a system for submarine telegraph cable in 1855, with calculations of the achievable data rate in relation to cable diameter and copper purity (bandwidth). He was also awarded patents for a mirror galvanometer (1858) and “siphon recorder” (1867) to record messages. Helmholtz resonator and coil Fig.21: the Woolrich Electrical Generator, the first commercial generator. Source: https://w.wiki/78sc (CC-BY-SA-4.0). Practical Electronics | February | 2025 Studied electrical resonance and invented the Helmholtz resonator during 1869-1871. He saw mechanics, heat, light, electricity and magnetism as a manifestation of a single force and published his ideas in “On the Conservation of Force” (in German) in 1877 – see pemag.au/link/abna Helmholtz also invented the Helmholtz coil, which is two electromag- Lord Kelvin resting on a binnacle (housing for a ship’s compass) while holding a marine azimuth mirror. Source: https://w.wiki/7Arz 57 Feature article Thomson’s submarine telegraph system could send one character every 3.5 seconds. He also significantly contributed to thermodynamics; the absolute temperature unit Kelvin (K) is named after him. He invented the Kelvin balance that allowed the unit of current (the ampere) to be precisely defined. Gustav Robert Kirchhoff 1824-1887 Kirchhoff’s circuit laws He made significant contributions in the fields of electrical circuits, spectroscopy and the emission of black-body radiation by heated objects. Kirchhoff’s circuit laws from 1845 are foundational to electrical engineering and physics. They allow an electrical network (circuit) to be analysed to determine the expected currents and voltages. Zénobe Gramme 1826-1901 Gramme machine (DC dynamo) In partnership with Hippolyte Fontaine, they built and manufactured an improved DC dynamo around 1873, called the Gramme machine, which produced smoother DC and higher voltages than prior machines. The duo also worked on other electrical devices. In 1873, he and Fontaine discovered that if the dynamo were connected to a DC supply, it would work as a much more powerful electric motor than any others at the time, which were of no practical use. Willoughby Smith 1828-1891 photo-conductivity Discovered photoconductivity in 1873 (when a material becomes more conductive upon exposure to light) in selenium. Sir Joseph Wilson Swan 1828-1914 first successful light globe Started experimenting with incandescent light globes in 1860, but was hampered by the lack of a good vacuum pump and a suitable power supply. In 1878-1879 he demonstrated the first incandescent light with a carbon filament in an evacuated globe, and he is regarded as the inventor of the first successful globe (see Fig.23). His house was claimed to be the first house to have electric lighting, but Moses Gerrish Farmer’s was likely first (see page 57). In 1881, he installed 1200 light globes in the Savoy Theatre in London, the first public building to have them. They were powered by an 88kW generator. Thomas Edison independently 58 Fig.23: These carbon filament bulbs show the blackening effect. This is due to the evaporated carbon condensing on the inner surface of the bulb. Source: https://w.wiki/7As8 developed the light globe, and both men obtained patents in 1880. Swan sued Edison. This led to a joint company being formed in Great Britain in 1883, the Edison & Swan United Electric Light Company (“Ediswan”), to exploit the inventions. Edison and Swan produced successful light globes, but there were many ideas for globes before them, starting with Volta. David Edward Hughes 1830-1900 printing telegraph and microphone Developed a printing telegraph system in 1855. In 1878, he described electronic carbon-powder-based sound pickups called “transmitters”, then being developed for telephones. He demonstrated how they worked, superseding the prevailing theory of the time and coining the term “microphone”. He developed a type of microphone but never patented it, thinking the work should be available for the benefit of all. In 1879, he likely detected radio waves before Heinrich Rudolf Hertz did in 1887/1888, but attributed the phenomena to electromagnetic induction rather than radio waves. James Clerk Maxwell 1831-1879 Maxwell’s equations Discovered that electricity, magnetism and light were different manifestations of the same thing. He produced Maxwell’s equations in 1861-62, which are the basis of electrical circuit and light theory. They explain how electric and magnetic fields relate. Oliver Heaviside produced the modern form (the Maxwell-Heaviside equations). His work combining all previous observations, experiments and equations into a consistent electromagnetic theory set the foundation for much of Fig.24: a Crookes tube, the basis of the cathode ray tube (CRT). Source: D-Kuru/Wikimedia Commons – https://w.wiki/7BiD 20th-century physics and led to the era of modern physics. Henry Woodward & Matthew Evans incandescent light globe Together they obtained a Canadian patent in 1874, then US Patent 181,613 in 1876 for an incandescent light globe that used a carbon filament in a nitrogen-­filled enclosure. They did not have enough money to develop their invention, so they sold the patents to Thomas Edison in 1879. Sir William Crookes 1832-1919 Crookes tube – the basis of X-ray tubes Invented the Crookes tube (Fig.24) around 1869-1875. It is a partially evacuated glass tube with an anode at one end and a cold cathode at the other that produces cathode rays. The shape of the anode causes a shadow to be projected by the cathode rays (electrons), some of which are blocked by the shape, while others that pass to the outside. It is the basis of X-ray tubes and the cathode ray tube (CRT) as was commonly used for TVs, computer screens, radar displays and oscilloscopes. Some CRTs used heated cathodes. John Dixon Gibbs 1834-1912 power transformer With Lucien Gaulard, he demonstrated a power transformer in 1881 and obtained US patent 351,589 in 1886. While transformers were not a new idea, this was the first that could handle power at industrial levels. Johann Philipp Reis 1834-1874 Reis telephone and speaker Constructed a type of telephone in 1861 with a range of 100m (Fig.26). It incorporated a microphone based upon a parchment diaphragm that altered the electrical resistance between Practical Electronics | February | 2025 The History of Electronics, part two two contacts when it vibrated, one of which was dipped in a drop of mercury. He also made a speaker that produced reasonable but weak sound, it was based on magnetostriction (ferromagnetic materials changing their shape when subjected to a magnetic field). Reis’ device could not reproduce speech intelligibly, so his patent was not upheld in a dispute with Alexander Graham Bell. However, David Edward Hughes later reported good results with the Reis telephone. Around 1947, the Reis device was tested by the British company STC, which confirmed it could transmit and receive speech, albeit faintly. The patent was partly invalidated because of a mistake in describing how the microphone worked; Reis said it worked by making and breaking electrical contact when it actually varied the resistance. Elisha Gray 1835-1901 Fig.25: the original writing and received copy on the Elisha Gray telautograph. Source: Popular Science Monthly, Volume 44, 1893-94. Musical Telegraph, telephone etc Invented an improved printing telegraph in 1872 (US patent 132,907). He also invented a “Musical Telegraph” that transmitted single musical tones over a telegraph link in 1874 (US patent 173,618). Oscillating steel reeds controlled by electromagnets produced the tones. See the video titled “Elisha Gray’s Musical Telegraph” at https:// youtu.be/YxxsTdjT7PA Gray secretly built a prototype telephone in 1876. Alexander Graham Bell’s lawyer got to the patent office shortly before Gray’s lawyer; thus, Bell got credit for the invention. The true inventor of the telephone is still hotly contested. Gray is, however, known for inventing one of the first electric musical instruments (Fig.27). In 1887, he invented the telautograph, a precursor to the fax machine, although he is thought to have conceived the idea as early as 1874. He patented it in 1888 (US patent 386,814). A user’s handwriting was transmitted using a stylus attached to a mechanism that transmitted the stylus’ coordinates over a two-wire telegraph circuit (see Fig.25). The system became very popular. Fig.26: a Reis telephone consists of a transmitter, receiver (C) and a glass dome, all powered by a battery (B). Practical Electronics | February | 2025 A telautograph can be seen in operation in the 1956 movie Earth VS The Flying Saucers on YouTube: https:// youtu.be/JCdnv3AP0eM?t=3683 William Grylls Adams 1836-1915 selenium produced an electric current Together with his student Richard Evan Day, they discovered that a platinum/selenium junction produced a current in 1876. Oberlin Smith 1840-1926 recording sound He proposed a method for recording sound by magnetic means in 1888. A thread such as cotton was coated with Fig.27: Elisha Gray’s Musical Telegraph from 1876. Source: https:// americanhistory.si.edu/collections/ search/object/nmah_703475 59 Feature article or contained a magnetic powder or short lengths of fine wire, which were then magnetised by the current from a microphone source. His ideas were implemented by Valdemar Poulsen (see his entry next month) but it is unknown whether Poulsen was familiar with Smith’s work. Sir Hiram Maxim 1840-1916 electric lamps While famous for designing weapons, he also made significant contributions to the development of electric lighting, including improved methods of carbonising and manufacturing filaments for electric lamps. John William Strutt 1842-1919 Rayleigh scattering & waveguides Also known as Lord Rayleigh, made the first theoretical analysis of electromagnetic waves in a metal cylinder (waveguide) in 1897. He discovered what is now known as Rayleigh scattering, along with many other discoveries. Nikolay Benardos & Stanisław Olszewski arc welding They used a carbon arc to soften metals to a plastic state and, in 1881, demonstrated the first practical arc welding. Édouard Branly 1844-1940 coherer (radio signal detector) Invented the coherer, the first detector of radio signals in 1890, based upon the work of Onesti (see his entry next month). It consisted of iron filings in an insulating tube with two electrodes. Tivadar Puskás de Ditró 1844-1893 telephone and multiplex switchboard Invented the telephone switchboard in 1876. The first one was built by the Bell Telephone Company in 1877. In 1887, he invented the multiplex switchboard for more efficient resource sharing. Augustus Floyd Delafield 1845-1927 homopolar motor He received US patent 278,516 in 1883 for a “dynamo-electric machine” based on Faraday’s homopolar motor design. The video titled “The Homopolar Generator” at https://youtu.be/ cQ5Ueouk _VY shows how it works. Sir Mark Oliphant built a famous homopolar generator at Australian National University (ANU). It was one of the largest ever built and could deliver currents of 2MA. It operated from 1962 to 1986 and was designed to produce extremely high current pulses for applications such as rail guns. Wilhelm Conrad Röntgen 1845-1923 X-rays Was investigating vacuum tube equipment produced by others in 1895 when he discovered X-rays. He was performing experiments with a Crookes tube and fortuitously had some barium platinocyanide on his hand, a chemical known to fluoresce in UV light. He noticed it glowing out of the corner of his eye, an area of the eye that’s very sensitive to light. He had the barium platinocyanide because of experiments he was doing with a Lenard window tube, a Crookes tube with a thin window to allow some electrons to escape into the atmosphere. Alexander Lodygin 1847-1923 patent 575,002 for a tungsten filament lamp. He sold the patent to General Electric in 1906. Pavel Yablochkov 1847-1894 carbon arc lamp Invented a kind of carbon arc lamp in 1876 called the “Yablochkov candle”. It would run for about two hours and could only be used once; it needed a large power source, produced a buzzing sound, UV rays, carbon monoxide and was a fire hazard. To power his lamps, Yablochkov invented a type of transformer based on Faraday’s discovery of induction to supply the required AC voltage for the lamps. The use of transformers to supply different voltages later became the basis of AC power distribution systems. Galileo Ferraris 1847-1897 polyphase alternator and induction motor He worked in the area of rotary magnetic fields in 1885. Such fields can be provided by a polyphase alternating current driving a system of coils or a single phase with windings arranged in a particular manner. His work led to the development of the polyphase alternator (effectively an AC motor operating in reverse) and the first induction (asynchronous) motor (Fig.28), but he did not patent it. He published his research on motors in 1888, just two months before Nikola Tesla obtained a patent for such motors. The invention of the polyphase alternator was a crucial event in the history of electrification. Alessandro Cruto 1847-1908 high-purity graphite light globe filaments Started experimenting with light globe filaments in 1880 and devised a carbon and metal filament lamps Fig.28: the world’s first AC motor from 1895 by Ferraris. Source: https://w. wiki/78se 60 Later known as Alexandre de Lodyguine, obtained Russian and European patents in 1872 for a carbon filament lamp. In the 1890s, he invented some metal filament lamps and obtained US Alexander Bell also co-founded AT&T. Source: https://w.wiki/7AsL Practical Electronics | February | 2025 The History of Electronics, part two process of making high-purity graphite filament, which he demonstrated at the Electricity Expo in Munich in 1882. This filament was more efficient than that used in Edison’s globe and produced a white light, unlike Edison’s yellow light. Also, it lasted for 500 hours, while Edison’s original version only lasted 40 hours. He established a factory in Alpigano, Italy, producing 1000 globes per day. After disagreements, he resigned from the factory and, after many changes of hands, it was acquired by Philips in 1927. Alexander Graham Bell 1847-1922 telephone, photophone etc Bell is most famous for his work in developing telephony. In 1875, he developed an acoustic telegraph to send multiple telegraph messages on one line (ie, a multiplexing method). He filed US patent 174,465 in 1876 for the telephone, slightly before Elisha Gray (as noted earlier). Bell got his “instrument” (as he called it) to work for voice only three days after he got the patent, using a liquid transmitter (microphone) of Gray’s design; his first famous words on the device were to his assistant, Thomas Watson, “Mr Watson, come here, I want to see you”. Despite his achievements with the telephone, Bell regarded his greatest achievement as the photophone in 1880. This enabled voice transmission on a modulated light beam that travelled 213m in one experiment. It had no real application until the invention of the laser (1960) and the optical fibre (1965) for optical transmission of information. It was jointly Some of the oldest audio recordings A collection of early sound recordings and associated links are available at pemag.au/link/abni The following link is to a recording made by Alexander Graham Bell in 1885. It was recovered optically by 3D imaging the grooves of the wax disc recording: pemag.au/link/abnj You can also see a video where the author searched through old texts to find sound representations and digitally converted them to the original sounds at https://youtu.be/TESkh3hX5oM invented with his assistant Charles Sumner Tainter. Thomas Alva Edison 1847-1931 microphones, acoustic telegraphy, fuse etc Edison was a prolific inventor and entrepreneur. In 1873, he demonstrated the varying resistance of carbon grains in response to pressure and built a rheostat based on that idea, but abandoned it due to sensitivity to vibration. It was useless for its intended purpose in telegraphy but came in handy later for carbon powder microphones, which he tested in 1876. In 1875, he performed experiments in acoustic telegraphy, the name for multiplexing messages on telegraph lines, receiving US patent 182,996 in 1876. He filed for US patents 474,230, 474,231 & 474,232 for a “Speaking telegraph” in 1877, awarded in 1892. The patents took so long to be granted due to the competing claims of Alexander Graham Bell, Emile Berliner, Elisha Gray, Amos Dolbear, J.W. McDonagh, G.B. Richmond, W.L.W. Voeker, J.H. Irwin, Francis Blake Jr and others. In 1877, he invented a phonograph. The device recorded on tin foil and could only be used a few times; nev- ertheless, he gained fame for it. In 1878, he demonstrated the machine in Washington, DC and was celebrated as a genius. He received US patents 200,521 and 227,679 for it in 1878 and 1880, respectively. In 1878, he established the Edison Electric Light Company and said, “We will make electricity so cheap that only the rich will burn candles”. In 1879, he filed and, in 1880, received US patent 223,898 for an “Electriclamp”. In 1880, he established the Edison Illuminating Company for electricity distribution in New York and, in 1882, opened the Pearl Street Station (600kW, 110V DC). In the 1880s and 1890s, there was the “War of the Currents”, the debate about whether electricity distribution systems should be DC or AC. Edison supported DC and saw AC as dangerous and unworkable. Edison invented a fuse in 1890 to protect his electrical distribution system. Next month That’s all we have room for in this issue. We will pick up where we left off in the third article next month, continuing our chronological list of PE electronic pioneers. A replica of the upstairs level of Edison’s Menlo Park lab. Source: https://w. wiki/7AsR The Edison light bulb enclosed in a cage. Source: https://w.wiki/7AsG Practical Electronics | February | 2025 61