The idea of an electric harmonica goes back to the 1920s. Pat Missin created  a very informative page about this topic. He also shows a picture of the Hohner  electronic harmonica prototype from the late 1970s. The prototype still exists. I had the fortune to take a picture of it at the harmonica museum in Trossingen, Germany. Unfortunately, nobody at Hohner can provide any information about its history. On top of that, the connector cable is nowhere to be found. Without that cable it is not possibility to get it to work. I would have loved to hear how it sounds.
The first really useful electric/midi harmonica was the Millioniser 2000, invented by Walt Miller. You can find the full story story about it online. It was quite an advanced technology for its time.

The DM48, developed by Erik Lekholm is the most recent addition to the world of electric harmonicas. The DM48 is a MIDI controller and needs to be connected to an external MIDI device.

Update: Lekholm instruments just recently released an updated version of the DM48.
The new model, DM48x has will add the following new features:
-Wireless playing over Bluetooth Low Energy (BLE) MIDI
-Ribbon controller: pitch bending or modulation via finger control
-Built-in battery, for five hours of wireless playing
-more onboard memory

In April 2021 a new MIDI digital harmonica by the Chinese company Mozka Digital was released.
Three models, HM12s, HM12 standard and HM12pro are available varying in features. All come with 78 onboard sounds. The instrument can also be used as MIDI controller for external synths.
It features wireless playing via Bluetooth. Some more info (mostly in Chinese) can be found here.
Brendan Power has a demo and review video about it on YouTube.

Cham-Ber Huang was the inventor of the Chordomonica I & II . His patent request for the Chordomonica II was granted in 1968 with patent# 1255465. Some brief info of the patent can be found on Pat Missin’s side as well as an extensive explanation of the tuning for both models.

Since 1981 Hohner discontinued the production of both models.
The patent ran out in 1983. There are now some different custom version of the Chordomonica available.

4 and 3 Octave version using the standard Chromonica cover plates

There is also a Chordomonica project website with another custom version using a customized Hohner Discovery 48.

In 1967, the famous harmonica virtuoso Tommy Reilly went to a silver smith at Covent Garden, London to commission a new chromatic harmonica made out of silver.
He talked about it in the following podcast dating back to 1973 (starting at 12:40):

At that time the  Silver Concerto harmonica was one of a kind. It was essentially a Chromonica II (3 octave, 12 hole instrument) made out of solid silver.

In Uwe Warschkow’s book “Harmonica Lessons with Tommy Reilly”, Reilly remembers the following:
“I always had the idea of a silver harmonica. Silver seemed to me the best material for it as it had proved its worth on the flutes. “
“The final impetus was that Robert Farnon composed for me ‘Prelude and Dance’. This work was both technically and musically so demanding, that I came to the conclusion that I can’t meet these demands with a standard ‘Hohner 270’.”
“After getting the prototype from the silversmith, Douglas Tate, then a student of mine, helped me a lot with his technical skills to get it perfect. The result was an excellent instrument. From this time I only played on this instrument. It did not only sound better, it also gave the harmonica more prestige, as it became evident when I met and talked with conductors and orchestra members at rehearsals, recordings, and concerts. They all played expensive instruments. Beforehand, I often had the impression that for them the harmonica was considered more or less as a toy, and then they were surprised that I was able to make music with it. That had changed now.”

Hohner Silver Concert
Reilly continues, “… at one of my next visits to Trossingen I showed my new harmonica to the Hohner management and suggested to include it into their product range. They hesitated. I had the feeling that they did not want it, but would not like to say no. When I told them, which was a fact, that also Yamaha was interested in buying the product license, they changed their minds. Yamaha? Under no circumstances!”
“Finally we made a contract and my development became a Hohner product and is known now as the ‘Hohner Silver Concerto’.”

Polle Concert Harmonica
Georg Pollestad was never quite satisfied with the sound of a mass-produced harmonica. After a concert in 1980 Sigmund Groven let him have a closer look at his ‘Hohner Silver Concerto’. Then he told Sigmund that he is going to build such an instrument himself. As Sigmund told us later, he had thought, this man is crazy. However a year later, before a concert he presented his first self-made harmonica to Sigmund. Sigmund was surprised and so pleased with the quality of the instrument that he presented Georg Pollestad and his new harmonica to the audience, and played some pieces on the instrument.
Since then, Georg Pollestad has continuously improved his first harmonica in close collaboration with Tommy Reilly and Sigmund Groven. Today, the ‘Polle Concert Harmonica’ is renowned throughout the world, and is played by famous soloists and harmonica enthusiasts. The instrument is made of pure silver and is absolutely airtight. Some of the major improvements include:
• specially shaped air channels in the body, resulting in a warm and rounded sound,
• a slide system that due to the minimal contact points is absolutely silent and does not stick,
• a mouthpiece with specially shaped holes and small engraved lines on both sides. The lines, also on the front of the covers, support gliding the instrument along the lips.
• LCD thermometer to determine correct play temperature
• two-screw quick change reed plate removal system

Please check also the separate article about the Polle concert harmonica

The Vermonia was invented by Erwald Hochmuth, Klingenthal. I assume, he worked for the VEB Klingenthaler Harmonikawerke (previously VEB Vermona). The patent# DD27979A was granted in 1961.
It is interesting that the slider can be moved to both directions in order to play different scales. Also, the harmonica body is adjustable to change the base key and chords.

 

Wolf Linde is a former R&D engineer at Hohner. For more than 50 years he was contributing to many of the inventions coming out of the Hohner factory. He was also a member of the CX 12 development team. His name is included in the corresponding patent# DE 41 29 817 C1. The 65 pages catalogue “Mundharmonika Kinder” (all color prints) by Wolfgang Ott shows all the extraordinary harmonica prototypes Wolf Linde produced over five decades.

Linde Tremolo Chromatic from 1963

Linde Chromatic from 1974

The full catalogue can be ordered directly from Wolfgang Ott via e-mail.

Update:

Recently, I came across this Linde Prototype. It is not part of Wolfgang Ott’s catalogue. I assume Linde sold it of or gifted it to a catalogue or friend.
This harmonica is really an interesting construction. The reeds are accordion rather than harmonica reeds. The slider rotates inside a tube. It has one design flaw though. There is no possibility to reach/repair an inner reed. A broken reed (or even a stuck valve) would render the instrument useless. Maybe that’s why it is only a prototype…

The Machino Tone chromatic was invented by the Torahachi Machino company of Tokyo in the 1950’s. According to several patents given in different countries, the earliest being from Britain (Patent 819441) and Switzerland (Patent 352220), the Machino Tone might have been available around 1957. The U.S. patent# 2,877,679 was granted in 1959.
As Pat Missin mentions on his website, a similar invention was already mentioned in patent# DE19221 by Adolf Glass Junior from 1882 (see also my previous post on the Glass Junior harmonica) .

There was a nice article written in the Garden State Harmonica Club Newsletter from 2006:

Our reliable expert, Stan Harper, recently
wrote of an intriguing Japanese harmonica…
Stan writes: In the 1950’s, a German, whose name
I forget, came to me with a Japanese harmonica
he was importing. He wanted me to play and
promote it. I had two or three which I eventually
gave to Andy Paskas [a passionate and eccentric
harmonica collector of Canadian background, well
known to many of us, including your editor].
It was the most powerful 12-holer I’d ever played.
It had no conventional mouthpiece and slide.
Instead, the airflow was directed by a [rocking]
damper, controlled by a pair of springs, which
normally prevented air from flowing through the
Db reeds, thus allowing only the C reeds to sound.
When the damper was rocked, by a tab [on the
back of the harmonica] it covered the C openings
and allowed the Db reeds to sound.
It was the best harmonica I’ve played to this day.
It had one major drawback: the damper had to be
worked up and down with the index finger. This
motion is contrary to how the hand works. I could
never play accurate rapid technique or cup it
properly. Here we have to disagree with Stan. We
heard him play this harmonica, and his technique
was quite rapid enough to suit most of us!]
The system is 100% superior to the mouthpiece
and slide setup. It never gummed up or needed
any care. I told the importer that if they could
make some sort of arrangement whereby an
operating lever could be placed on the right side
like the slide button, it would be the best harmonica
in the world. As it was, however, it was a loser.
(There were many wonderful harmonicas, but
bigger companies either bought them out or put
them out of business by preventing stores from
handling them.)
Well, Stan, we don’t remember the German
importer’s name either, but his company was
“Worldwide Musical Instrument Co.”
He had been seeking someone to write and design
a small sales brochure for him. This was not long
after we had written an instruction book for
Hohner and someone at Hohner recommended us.
We got the assignment, but probably forgot him
deliberately, because he stiffed us on some of the
money he owed…quite different from Hohner, who
always treated us right; we still have some spare
reeds and springs and other odds and ends they
gave us years ago.
The name of the harmonica was “Machino Tone”.
This had nothing to do with machinery; the
inventor’s name was T. Machino. Here are
pictures of both the “Machino Tone” and the
brochure we created for it.
As Stan says, it was a terrific concept…easy to
blow, and quite loud. Also, as he says, there was

no slide to stick, or get “gummed up”. Despite a
preference for a 16-holer, your editor played the
Machino for quite a while (using his middle finger
on the lever), but it eventually sort of fell apart
(the Machino, not the finger). It needed three
combs…one between the reed plates, one above,
and another below. The above and below combs
were not made well, in our opinion, and they were
very hard to repair–to make airtight—once they

disintegrated. Of course, Stan’s point about
the somewhat awkward button or lever is
well taken, too. It was a whole new
learning experience. But, as we stated
above, Stan flew over it pretty darn well,
no matter what he says now.
Today, with molded plastic combs and
such, it might be possible to make such an
instrument that would be really durable.
With a button in the right place, it would be
fantastic!
Incidentally, the Worldwide Musical
Instrument Co. was located at 404 4th Ave.,
New York 16, New York, across the street
from Hohner’s old location at 351 4th Ave.
(Note the nostalgic two-digit postal zone,
dear REEDers. Today it’s zip 10016, and
real estate values on 4th Ave. have been
boosted by simply renaming it Park Ave.
South.)

Torahachi Machino also invented two tremolo chromatics with a similar mechanism.

The Meteor chromatic must have come out around 1954, at least that is the time when the patent# 8724 was granted to Helmut Hoyer, Klingenthal. Helmut Hoyer worked for the VEB Klingenthaler Harmonikawerke. The interesting thing about the Meteor chromatic is its curved mouthpiece as well as the assembly of the push button. The button is attached to a lever. The lever pushes against a spring to change the position of the slider and therefore to change keys.
VEB came out with two models. One with a gold the other with red labeling.

In 1937, Archimede Mancini founded his first factory, “La Fisarmonica” together with Egisto Bontempi in Potenza Picena, Castelfidardo, Italy. After the war in 1950, Mancini relocated his company to the city of Pesaro, Italy. He passed away in 1976.

The design of his first chromatic harmonicas pretty much resembled the Hohner Chromonica.

The 10 and 12 hole chromatics that followed were very unique, stylish, and had very particular shapes. They were branded “London Pride” and “Mondial”.

So far I have seen the Mancini chromatics in silver, black and red.

At the beginning of the 1950s Hohner came out with two new models, a 10-hole Chromonica I De Luxe and a 12-hole Chromonica II De Luxe. The patent# 853853 was issued to Walter Hohner in 1952. More info can be found on Pat Missin’s website. As Pat mentions, the US Design Patent# 166750 was also issued to Walter Hohner the same year.
I’ve recently read an interesting article about John Vassos. Especially this part got my attention:
In the late 1940s, John Vassos was hired by Hohner to design harmonicas and accordions with his signature modernist and streamlined aesthetic, primarily aimed toward the American market. Vassos’ design drawings feature marks resembling air whooshing past his harmonicas—musical spacecraft traveling through the galaxy of his imagination.
I could actually imagine that John Vassos is the father of the Chromonica Deluxe design.

The Melodia II manufactured by the Czech company Lignatone might have taken some cues from the De Luxe chromatic.

Update:
I finally had the chance to go back to the harmonica museum in Trossingen to take a closer look at one of the most unique and stunning chromatic harmonicas out there, the Chromonica IV De Luxe. Martin Haeffner from the museum and Gerhard Mueller from Hohner were kind enough to allow me to spend some time analyzing and taking pictures of the instrument.

I’ve always wanted to get a deeper knowledge of that instrument. Maybe one day I will even be able to re-manufacture one.
According to its patent, it consists of two combs with two pairs of reed plates.
I was curious to find out how those different reed plates were tuned and how they interact with one another. I made a short recording carefully blowing into the instrument and utilizing all three buttons:

I quickly realized what was going on:
when blowing into one hole without using any buttons, one can hear two notes an octave apart.
E.g. when blowing into the first hole one will hear the middle C# and the C# one octave below. Contrary to a regular C tuned chromatic, one needs to press the right button in order to hear the middle C. Otherwise, the order of the notes is identical to a standard 3 octave C tuned chromatic.

The purpose of the two buttons on the left side is to allow for single note playing.
E.g. when only pushing the top left button and blowing into the first hole, the middle C# will play. When only pushing in the bottom left button the C# below middle C will play. This gives the De Luxe IV a range of 4 full octaves.

I was able to take off some of the outer covers to see more of the internal mechanism of the instrument.
Based on the fact that the reed plates are custom made and some scribbled notes on the reed plates, it was clear that this was the only prototype. Unfortunately, this instrument never went into mass production.
The De Luxe IV consists of many small parts interacting with each other, i.e. the locking mechanism of the left buttons. It was probably just too difficult to mass produce this instrument.

The Magnus Harmonica Corporation (founded in 1944 ) started producing plastic harmonicas (US patent US2407312A) at the beginning of 1948. Besides chromatic harmonicas, the Magnus corporation also produced 10-hole diatonic and tremolo harmonicas. More information on the different harmonicas as well as a short and a more extensive description of the Magnus corporation history can be found on Pat Missins’s website.

The interesting invention is that the whole harmonica was made out of plastic, including the reeds. Furthermore, the slider mechanism works similar to the one used for the Böhm Chromatic with movable reed plate: in this case, the reed plates and the comb are moved to the left when the button is pushed.

Other harmonica manufacturers like the British Mouthorgan Company (BMO) were striving for some of the Magnus success: