Why didn't you use existing PC-104 boards?

Several reasons:

• While there a many types of boards available in the PC-104 format, none directly emulate the subsystems in a satellite.
• EyasSAT must run for a reasonable period of time from batteries. Most commercial PC-104 boards require considerable current and are therefore not suitable
• Most PC-104 boards are overkill for what is needed in EyasSAT. For example analog to digital conversion boards usually have a dozen or more channels when only 8 or so are needed for the thermal system in EyasSAT.
• Adding custom boards would require each to have the hardware needed to interface to the PCI bus used between PC-104 boards. That's hardware not otherwise needed. Additionally, the firmware in each custom board would have to implement the PCI bus.