V=IR, V/I=R if you want 100mA to flow thru the circuit take 2.8/0.1 and you get 28 Ohms.

It is always a good idea to use a current limited power supply for testing.

I'm not an EE so only know enough ot cause trouble. Corrections welcome.

phew! Oh yes, thank you for checking and for the thoughful reply.

Many answers in the replies said exactly this (note the post was nearly a year ago...I have since wired it all up, completed the artwork and exhibited it at three venues!) but much appreciated for taking the time.

yes there are some things here that take some getting used to, and a few small bugs because Mastodon is non-commercial and it is up to users, not teams of paid testers, to report errors.

There are also other reasons you might not see replies on an old post. Eg:

1) Many people automatically delete old posts
2) Many people reply privately
3) Some people's instances may not be 'federated' with your instance

the third example above is one that can be hard to understand as a new user, but becomes easier over time. There are plenty of explanations online about federation but I learned mostly by just interacting on here and picking up meaning slowly.

And welcome to Mastodon!