An embedded engineer, a lot of tooling, and a fair few AI agents.
zx9 is the design and build service of Zolex Labs Ltd. We're a small UK company and the engineering is done by someone who has been writing firmware and designing boards for decades, mostly for other people's products: fire safety systems, heating controls, radio networks, test equipment, that sort of thing.
Over the last couple of years a lot of the day-to-day work has moved over to AI agents, and I think that's changed the maths on small products quite a bit. A lot of what used to take the time on a small product now goes much quicker, and the engineer's time goes on the bits that need judgement. Which means a product that only ever needs a hundred units can be worth doing now, when it maybe wasn't before.
It's not magic and we don't pretend it is. An engineer still goes over every board. Prototypes still come back with mistakes on them, and that's what the prototype is for. What's different is how quickly you get to that first board on the bench, and what it costs you to get there.