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Kicad PCB design with XH717 ADC to support Klipper load cell
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Prototype designs for klipper load cell ADC implementations.
STM32F072 and HX717 based strain gauge for use as a Klipper load cell.
Initial batch ordered for testing with JLCPCB. About 5.5 USD cost per board.
Firmware and configuration tested with current community test branch.
Smallish size, 20x50 mm footprint. M2.5 mounting holes. Fab house added the smaller tooling holes...
4 layer PCB all parts on top side.
MCU selected for crystal less USB operation with minimum of 64k flash for firmware.
Separate low noise, high PSRR for analog Vdd supply.
HX717 default data rate 320 Hz. Adjustable with solder jumpers.
[!NOTE]
Crystal less main clock is problematic with Klipper and maybe the HX717 code.
Works fine 90% of time, but suffers from occasional timeouts during probes.
Addon for a FYSETC H36 v1 Toolhead board. Uses the 2x6 2mm expansion pin headers for mounting. Hardware spi works for the H36_COMBO. The H36_COMBO_V2 changed the header pins.
Straight needle 2mm 2x6 female pin header (4.3mm plastic body) fits with 6mm standoff but doesn't clear the IO.0+1 with a cable installed. A bent needle 2mm 2x6 header works (6mm plastic body) with 8mm standoff after bending the pins to be straight.
4 layer PCB all parts on top side.
Separate low noise, high PSRR for analog Vdd supply.
HX717 data rate 320 Hz.
Klipper configs for ADS1220/HX717 configs.
Users have reported software SPI is functional on the v2 boards.
H36 V1
sensor_type: ads1220
cs_pin: toolhead:PB6
spi_bus: spi1a
data_ready_pin: toolhead:PC13
sensor_type: hx717
sclk_pin: toolhead:PB3
dout_pin: toolhead:PB4
H36 V2
sensor_type: ads1220
cs_pin: toolhead:PA14
data_ready_pin: toolhead:PA1
spi_software_sclk_pin:PB7
spi_software_mosi_pin:PB13
spi_software_miso_pin:PA15
spi_speed: 256000
sensor_type: hx717
sclk_pin: toolhead:PB7
dout_pin: toolhead:PA15
4 channel ADS131M04 for underbed applications. Each load cell can be individually measured and digitally summed.
8.192 MHz clock hardware generator.
Separate low noise, high PSRR for analog Vdd supply.