I received these interesting thoughts from a hackerspace acquaintance which make me wonder if it would be feasible for the $25/badge budget to use an FPGA that would run an open source "soft-core".

This person thought that the RISC-V badge is a great starting point (see earlier project log).  The connector between the badge and the processor could be useful for reuse and upgrades.  However, the connector that was chose is not the most common or easiest to work with.

The Parallax Propeller is an open source microcontroller that is available in a DIP form factor.  It would be nice to provide people with options and the DIP form factor is very convenient.  There are several existing boards that fit that DIP form factor:

• Propeller Chip 40-Pin DIP
• Propeller FLiP MCU Module
• DIPFORTy1 "Soft-Propeller"

It might useful to create some RISC-V modules in the same form factor.  Potentially, one version could have the FE310, and one with a soft RISC-V running in an FPGA.  

Propeller pinout for the MCU interface could significantly reduce the risk of this development.  The badge hardware could be tested with existing hardware while new MCU modules are designed.  The badge could be given away with the least expensive MCU module, and they can upgrade it by building or purchasing another module

An alternative module form factor could be the Arduino Nano pinout for the MCU interface.  That would enable a bunch of MCU choices, and this FPGA board that may be able to implement a RISC-V processor.  The Adafruit Feather form factor is another possibility.

Thanks for your consideration,

Drew