NS1nanosynth, as many other sound generating equipment (as opposed to controllers), needs a USB host device to connect with.
The most part of the MIDI keyboards are USB ‘device’ devices..
There are two ways of connecting a keyboard directly:
1(normal)-buy a MIDI host to device (Kenton makes some)
2(hacker/coder)-use the standard midi cable with an adapter AND a new firmware…
Regarding the second one, the NS1’s arduino have the RX and TX pins on the connector and you could hack a MIDI DIN connector and an optocoupler to the NS1 quite easily…
Then, by mixing the code on the NS1 with the MIDI libraries for Arduino, you obtain the standard midi (DIN cable) connectivity!