The Skinderviken Transmitter Button

In 1931 This text appears in  Telephony Magazine:

"It was customary in the past to refer to the bridge back transmitter as standard. Since the advent of the Skinderviken Transmitter Button however, opinion has been passed in favor of this new type of transmitter, which operates on the principle of complete vibration.  (i.e. the whole carbon chamber vibrates)"

The big advantage was that bridge back transmitter buttons operated at between 2 and 20 Ohms. The Skinderviken operated at 80 Ohms. That's about 75% less power. Today we'd list that on our LEED certification. Ads for the device can be found as early as 1919. The units were still in use a decade later becoming common-enough to appear in the parts lists of children's electrical projects.

So to start with, what is a bridge back transmitter button? Let's go back to 1878 and early carbon mics.It was known that if two conductors were in contact with each other, the increase of pressure between them diminishes their electrical resistance. In 1878, Thomas Edison exploited this behavior and came up with the the first practical variable resistance telephone transmitter. He called it a "Button transmitter." More here.

It consisted of a mica diaphragm clamped an iron case.Over that is an ebonite cap mouthpiece.  Applying pressure to the mica forms a vibrating cover to the chamber between the ebonite sides. In that space is carbon powder or lamp black. The amount of pressure on the carbon is adjusted by a set screw. Sound waves hit the diaphragm causing it to vary its pressure upon the carbon producing variations in the electrical resistance of the circuit.  This is not a "button" in the touch-screen cell phone sense of the word. More here.

The Skinderviken was designed to replace the original transmitter in telephone handsets. This may sound like a cheap knock off but Johan Skinderviken was awarded patent US1275776 on August 13th 1918 for the device. In his design the transmitter is directly connected to the diaphragm. A conical shell between them contains the carbon powder. He had filed the submission on November 7th, 1917... barely a year before the ads started appearing in electronics magazines.It was not his first telephone patent but his second, the former being granted in 1916. That one notes that he is a subject of the king of Norway, and resident of Chicago. In 1922 he sold the international rights to his button (retaining US and Canada) to Mikro Ltd.

The Microphone Part 3

The microphone is easy to forget. I forget that there's one built into my answering machine and my mp3 player. They all descend from one experimental microphone invented by Emile Berliner in 1876. but what's amazing is that the man that made this mic work had only a rudimentary understanding of electronics and no knowledge of physics.

Emile came to America from Germany in 1870. He did not go to work directly for Bell telephone. He actualy shoveled manure at a livery in washington D.C. While hosing off his shovel he often thought about the new technology of the wireless. He was a tinkerer. He got a part time job as lab assistant to one Dr. Fahlberg (the dude who discovered saccharine) .

He studied Alexander Graham Bell’s telephone. Bells phone consisted of two identical cases containing an electro-magnet and a diaphragm connected by an electrical circuit. Unfortunately , the message transmitted wasn’t very clear. The invention had a good receiver but a poor transmitter.

Emile thought he could do better. Working alone in his rooming house he fashioned a new type of microphone which he called a "loose-contact" transmitter. It was a type of microphone, which increased the volume of the transmitted voice. It was a type of carbon microphone that varied the contact pressure between two terminals as a sound pressed against the microphone. This was much better than the crude microphones before it. Great detailed history here: http://www.du.edu/~jcalvert/tech/microph.htm

He sold out to Bell immediately and hung up his shovel. Berliner worked for Bell Telephone in New York and then Boston from 1877 and became an American citizen 4 years later. He left in 1883 and returned to Washington and established himself as a private researcher.

The Microphone Part 2

The first Microphone was the Carbon Microphone. The word "microphone" comes from the Greek word "micro", which means "small", and another greek word "phone" that means "voice". It first appeared in a dictionary in 1683 as "an instrument by which small sounds are intensified". In this era the word was meant the acoustical hearing devices such as the ear trumpets and megaphones of that era. While Wheatstone was the first to use it in the electrical context, the word predates everything.

David Hughes was born in London in 1831 and grew up in the United States. He like Wheatstone was a musician. Hughes became a professor of music at St. Joseph's College in Bardstown, Kentucky, in 1850. He also developed an interest in electrical engineering and brought his two main interests together when he began studying the transmission and amplification of sound. Also similar to Wheatstone, his introduction to electronics revolved around the Telegraph. In 1855, David Hughes received his first U.S. patent for a printer used with a telegraph instrument. In 1857, Hughes returned to London and took his work with him.

In 1878, Davie-boy invented the carbon mic. Hughes was working on a telephone receiver and found this loose contact in a simple circuit made of a battery and a telephone receiver. He noticed the loose contact created a situation where sounds in the receiver matched the vibrations on the diaphragm of the telephone mouthpiece.

What makes this interesting is that Bell, the inventor of the telephone hated the battery. Mr.Bell did not want to use battery power in his telephone system at all. Many of his his early phones had no batteries but had great difficulty in receivinng the weak signals. If he had succeeded, Hughes would never met that loose wire. So many tinkerers were working on this faintmness problem at roughly the same time. Emile Berliner had a loose-contact metal-to-metal transmitter. At the same time Hughes was wiggling 'carbon rods, a man named Blake was workign with carbon blocks and Mr. Hunnings was pressing forward with a carbon-granule design. Interesting that both Berliner and Hughes used the term "microphone" to describe their transmitters... (diagram from http://www.doramusic.com/patentdetails.htm) THEY RULE!)

So anyway there's Hughes wiggling that wire. He was wiggling it and thinking about the shortcomings of Edison's carbon telephone transmitter. It was here that he realized that the arrangement was causing variable electrical resistance. The variation in resistance was such that it produced an exact representation of the sound waves as to height, length and form. He published the results in 1878 but refused to patent it!

Well-honored in his own lifetime, Hughes was the recipient of many honors and awards including a Fellowship of the Royal Society, a Grand Gold Medal in 1867, the Royal Society gold Medal in 1885, and The Albert Gold Medal, Society of Arts in 1897. It's no surprise I've written about him before.