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Rev 6.4 (Dec 2021)

Bug fixes to 6.3:

  • Fix ISENSE bug in 6.3, by adding diode to clamp negative outputs. Adds D68, R71, and C63.
  • Correct digikey part number for J9 (barrel jack)

Rev 6.3 (Nov 2021)

Preliminary/development release. Not recommended.

Bug fixes for rev 6.2:

  • Switch back to PCA9685
  • Correct swapped silk designators for R28/R29
  • Change C59 from 0.01uF to 0.1uF (VHV_TARGET_PWM filter)
  • Change R29 from 511ohm to 0 (Current integrator output filter)

Errata:

  • Large currents cause negative voltage on SAMG input pin, which can reset the device when too much liquid is on the board. This board should only be use with ISENSE trace cut (optionally, can add resistor and diode to re-enable use of ISENSE line).

Rev 6.2 (Aug 2021)

Preliminary/development release. Not recommended.

Updated for current parts availability.

  • Switches MCU from STM32F13 to ATSAMG55
  • Adds negative supply rail for current sensing op-amp
  • Changes PWM driver from PCA9685 to PCA9532
  • Adds current sense input to MCU ADC
  • Makes several other functionally equivalent parts changes, that should be transparent to software.

Rev 6.1 (Nov 2020)

Functionally equivalent to rev 6, but fixes several issues with the rev 6 design.

  • Fix several labeling errors
    • RED/GREEN LED labels backwards for HV enable switch
    • R41/R42 silkscreen labels swapped
    • Incorrect top plate steering resistor silkscreen labels
    • Incorrect PWM channel labels in silkscreen
  • Move HV_CLK and HV_DIN to SPI pins PC10 and PC12
  • Fix footprint pin assignment error on U16 (reference diode)
  • Add low-pass filter to high voltage feedback lines to ADC
  • Add pulldown to VTARGET output to prevent enabling HV when STM32 is in reset
  • Move HV enable switch to opposite side of board, away from exposed HV nets
  • Add HV507 low-side augment FET to improve capacitance sensing noise
  • Switch to 2-wire RTD pins, and combine all 4 sensors into one 8-pin header
  • Fix BOOT0 polarity, so that STM32 boots to application by default
  • Add BOOT1 pulldown resistor
  • Add 1000pF capacitance on RTD inputs for rejection of HV coupling
  • Increase HV voltage divider resistance to save power

Rev 6 (April 2020)

  • Switch to STM32F4 for main controller (instead of raspberry pi)
  • Switch to 5V input voltage from micro-USB or aux barrel connector
  • Add current sensing for top-plate driver
  • Use isolated power supply reference ground for HV507 supplies (5V_ISO and V_HV)
  • HV supply uses op-amp feedback for regulation (instead of linear regulator)
  • By default MCU measures and controls HV supply voltage
    • Optionally, steering resistor can select trim pot for voltage control
  • Add fourth RTD sensor input
  • Convert to single component revision (0.5.1 -> rev 6)