PurpleDrop 6.4

This release switches to the SAMG55 MCU, due to a lack of part supply.

• Switches MCU from STM32F13 to ATSAMG55
• Adds negative supply rail for current sensing op-amp
• Adds current sense input to MCU ADC
• Makes a few other functionally equivalent parts changes, that should be
  transparent to software.

PurpleDrop 6.1

PurpleDrop main board v6.1 release. This fixes several important problems with the v6.1 design. See ChangeLog.md for details.

PurpleDrop 6.0

This version is not recommended for use. Rev 6.1 has all the same features, but fixes several bugs in Rev 6.0 that require substantial re-work.

This version updates the PurpleDrop board to use an STM32F413 microcontroller. It adds:

• USB peripheral for control and power
• Electrode capacitance sensing
• Adds a fourth RTD temperature sense amplifier
• Software controlled high voltage setting

v0.5.0

Fab notes:

• 4 layer pcb (no blind/buried vias)
• 6/6 mil trace/space
• 0.4 mm minimum hole size
• immersion gold plating recommended
• purple mask recommended