The current version of the hardware design is v1.8.
It comes in two variants, a minimal variant that blocks only the four pins necessary for it to work (v1.8), and a second variant (v1.8shim that covers the remaining two power pins (no electrical connection, simply for added stability) and provides a mounting hole.
The old version v1.7 contains an error. This error can be corrected by "misusing" the pin for the external voltage and adding a connection between the jumper pin and the resistor R1 (the pin that is connected to the internal Vcc). This has been corrected in all later versions and I would not recommend using this old version PCB.
The directory breadboard contains pictures of the early experiments on a breadboard.