I use 854370
Which seems to be
Electrical machines and apparatus, having individual functions,
not specified or included elsewhere in this chapter; parts
Other machines and apparatus:
So far so good.
854231 would be
Electronic integrated circuits; parts thereof:
Electronic integrated circuits:
Processors and controllers, whether or not combined
with memories, converters, logic circuits, amplifiers,
clock and timing circuits, or other circuits....................
which might be the thing if my stuff had a processor (does an ATtiny count?) , but at this time it does not.
Disclaimer: I have no idea what I'm doing.