From 8ef0f7d7e3d3b2ac7bc1e80ed3295ceca6bba4e7 Mon Sep 17 00:00:00 2001 From: DavidvtWout Date: Mon, 11 Sep 2023 00:51:14 +0200 Subject: [PATCH] spi_temperature: Limit maximum temperature in MAX31865.calc_adc() to melting point of platinum (#6320) Limit the maximum temperature in MAX31865.calc_adc() to the melting point of platinum. Above this temperature the Callendar-Van Dusem formula does not make sense. The default value for max_temp is 99999999.9 and at this temperature the result of this formula is negative. This sets max_sample_value to 0 which causes the mcu to shutdown. Set max adc value to (1<<15)-1 . This is needed because the max value of the adc register of the MAX31865 is 0b1111 1111 1111 1110 which represents 32767 and not 32768. Signed-off-by: David van 't Wout --- klippy/extras/spi_temperature.py | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/klippy/extras/spi_temperature.py b/klippy/extras/spi_temperature.py index 9970a28d..77033b1b 100644 --- a/klippy/extras/spi_temperature.py +++ b/klippy/extras/spi_temperature.py @@ -320,9 +320,10 @@ class MAX31865(SensorBase): def calc_adc(self, temp): # Calculate relative resistance via Callendar-Van Dusen formula: # resistance = rtd_nominal_r * (1 + CVD_A * temp + CVD_B * temp**2) + temp = min(temp, 1768.3) # Melting point of platinum R_div_nominal = 1. + CVD_A * temp + CVD_B * temp * temp adc = int(R_div_nominal / self.adc_to_resist_div_nominal + 0.5) - adc = max(0, min(MAX31865_ADC_MAX, adc)) + adc = max(0, min(MAX31865_ADC_MAX - 1, adc)) adc = adc << 1 # Add fault bit return adc def build_spi_init(self, config):