Offline POS Machine Development with 4-Digit Protocol

I'm in need of a tool similar to an offline POS machine. This device will primarily be used for handling sales transactions and should be capable of processing both credit and debit card payments.

Ideal Skills:
- Experience in hardware development and POS system design
- Knowledge of secure transaction protocols
- Ability to create user-friendly interfaces

Please note that the project does not require the machine to include a built-in receipt printer. Bids from freelancers with relevant experience in creating similar devices will be prioritized.