Send it somewhere it matters.
The development of Backyard Hero is a very capital-intensive project. Involving significant compute costs for hosting, as well as costs of production for PCBs and hardware, it eats up quite a bit of cash. While this all is currently offered the community for free, people may be compelled to show appreciation through donating money which is awesome!
Though, at least right now, it's not necessary. Through my using passion projects in place of long deferred therapy, a frugal lifestyle that leaves just enough for fun stuff like this, and generally a disdain for people capitalizing every damn thing, I see no need to collect personal donations right now. Times are hard for a lot of folks right now, and for them every dollar counts. Sure, we're in the game of quasi-literally lighting money on fire, but the entire purpose of this project is putting a great show in the air while putting more in your pocket.
If you still have the need to throw money around after reading that, there is still somewhere for your money to go - There are many nonprofit organizations that are struggling to provide services to people that need it. One that I can personally attest to from almost a decade of being with them as a volunteer is Special Olympics of Washington (SOWA). SOWA does absolutely amazing things with the limited funding they get. They provide an invaluable platform and community for absolutely spectacular athletes to compete and overcome difficulties that most of us will never fully understand. It assembles the finest group of parents, athletes, volunteers and paid staff to make all this happen and I've always been confident that every minute and dollar i put towards it goes towards good. So I'd propose sending some cash their way (tax deductible!), or to your local Special Olympics chapter.
Special Olympics
Donate directly to Special Olympics Washington, or find the Special Olympics chapter local to you.