Adding entropy from external source into random number generator - how?

Hi all. I was pointed to this mailing list, so I hope my query is 
reasonably on topic.

I've developed simple firmware on a microcontroller which uses the values 
of multiple floating analog inputs to generate random numbers. I'd like to 
use this as an external source to add entropy into a FreeBSD system.

I think the best way to do it would be to call random_harvest_queue(...), 
but what do I use as the source enum (see /usr/include/sys/random.h)? 
ENTROPYSOURCE, I guess?

I believe it's also possible to open /dev/random for write to inject 
entropy, and I'm sure I saw mention of this being available around 12.0R, 
but I cannot find any mention of that scenario in the man pages.

I guess the other question to ask is whether ~45 kilobytes per second of 
additional entropy is even useful in a typical situation? There's no 
strict security requirement or anything like that, it's really just a fun 
project that I'm hoping to actually use. :) All entropy is good entropy, 
right?

Thanks in advance.