v1.0 Errata: R5 Removal

[thatch]

Background

The intention behind J5 was to have two input pins to support a 3-position switch using software-configurable pullups (B5 and B6). After initial investigation for outputs (called L* in schematic), we determined that physical pin 7 was pulled HIGH on boot, and didn't want relays accidentally triggering before the Python code could start. The four pins we use that are pulled HIGH in default device tree, we included a stronger pulldown resistor, regardless of whether they were intended for input or output.

The problem

The stronger hardware pulldown in tag:v1.0 (R5, 1k) fights with the software pullup (guessing about 5.6k), resulting in a max 0.5V which is still considered LOW. Looking at the physical boards, this could have been a problem as early as tag:v0.3, but the pulldown was only 10k in my locally-built v0.3 and v0.4 boards.

Resolution

Desolder R5