In 2000, Ellsworth attended her first Commodore exposition, where she unveiled a prototype video expansion for the C64. This project later evolved to become the CommodoreOne, a.k.a. the C-One, and C64-DTV, and a video on YouTube "Expo Jeri 1st". Ellsworth then began designing computer circuits that mimicked the behavior of her first computer, the Commodore 64. In 2002, she designed the chip used in the C-One as an enhanced Commodore 64 which could also emulate other home computers of the early 1980s, including the VIC-20 and Sinclair ZX81. She and her fellow developer displayed the C-One at a technology conference, which led to Ellsworth receiving a job offer from Mammoth Toys, which hired her to design the "computer in a chip" for the Commodore-emulating joystick. She began the project in June 2004 and had the project ready to ship by that Christmas. It sold over a half-million units, in the US, Europe, and elsewhere. She didn't receive payment, nor the commission she was owed, but a story in the "New York Times" brought her to the public eye.