MATRIXED KEYBOARDS  (FATAR type):

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The keying (or multiplexing) of the keyboards avoids the connection of the 61 keys on a large connector. (Generally quite expensive and cumbersome).
Ancient  keyboards had indeed 61 direct contacts.

This reduces the number of contacts of the connector to 16 points (8x8) instead of 64. This in 2 rows of 8 contacts.
The old keyboards had a single 8x8 connector for the 61 keys with only one touch per key. Newer keypads have two contacts per key (one contact up and one contact down), allowing the electronic system to test the speed of key depression.) I use this feature to control my pipe organ in expressive-sensitive mode with my KI6x8x8_MIDI_USB cards that directly interfere with it. The typical scheme is as follows:

One can easily test the circuit board by wiring 2 pins on the boards. Or hitting a key on the keyboard when keyboard is disconnected.
My boards KI6x8x8_MIDI_USB ou KI8x8x8_MIDI_USB can control from 1 to 16 keyboards.

ADVANTAGES and DISADVANTAGES of this TECHNIC :

Connecting such keyboards is fairly simple and ultra-fast. Because only 2 connectors are to be plugged to these keyboards. As they can be directly connected to my boards MIDI/USB KI6x8x8_MIDI_USB which output the MIDI controls on any USB connector of PC or MAC.
Very economical because FATAR type TP6LP type DF (Diode Forward) keyboards cost only a hundred Euros: 175 € exactly and are of excellent quality.
At times, it is important to point out the problems that can be encountered over time with these keyboards: Indeed, the rubber bands contacts and micro-spring are very fragile and can deteriorate over time. Their troubleshooting is also very difficult, because you have to disassemble the keys to access it. Nothing says that in 10 or 15 years, these rubber ribbons will still be available.
Fine particles can also alter the contacts, (this has happened to me) when the keyboard is transported in sometimes dusty environments.
That said, the small soft cone provides these keyboards a mechanical detachment effect that beautifully simulates true pipe organ keyboards.

In my opinion, nothing beats classic keyboards with HALL type magnetic sensors, which interface directly with my KI7_MIDI_USB cards. The wiring is a little longer, but the guaranteed longevity is absolute.
They equip the big organ of 5 keyboards that I built in Rians since 2005, without the slightest problem.