60 lines
1.6 KiB
Python
Executable File
60 lines
1.6 KiB
Python
Executable File
#!/usr/bin/env python3
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import math
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# Script to generate NTC lookup table
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# ^ Vcc
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# |
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# [RES]
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# |
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# +-- Vadc
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# |
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# [NTC]
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# |
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# _|_ GND
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# ///
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adc_res = 12
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ntc_value = 10_000 # at 25°C
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resistor_value = 10_000
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ntc_beta = 3380 # at 25°C
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steps = 64
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# NTC resistance to temperature (°C) conversion
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def resistance_to_t(ntc_r):
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# Standard B-parameter equation
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# T = 1 / (1/T0 + 1/B * ln(R/R0))
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inv_t = 1/(25 + 273.15) + math.log(ntc_r/ntc_value)/ntc_beta
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return 1/inv_t - 273.15
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# Resistor divider percentage to NTC resistance conversion
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# x = NTC / (NTC + RES) => NTC = RES * x / (1 - x)
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def x_to_r(x):
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x = max(0.0001, min(0.9999, x))
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return resistor_value * x / (1 - x)
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# Use 4096 for cleaner divisions
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adc_max = 2**adc_res
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step_size = adc_max // steps
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values = []
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for i in range(steps):
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adc_val = i * step_size
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x = adc_val / adc_max
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r = x_to_r(adc_val / adc_max)
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t = resistance_to_t(r)
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values.append(int(round(t)))
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def to_c_array(values, ctype="float", name="table", formatter=str, colcount=8):
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# apply formatting to each element
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values = [formatter(v) for v in values]
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# split into rows with up to `colcount` elements per row
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rows = [values[i:i+colcount] for i in range(0, len(values), colcount)]
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# separate elements with commas, separate rows with newlines
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body = ',\n '.join([', '.join(r) for r in rows])
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# assemble components into the complete string
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return '{} {}[] = {{\n {}}};'.format(ctype, name, body)
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print("uint8_t ntc_step_size = {};".format(int(step_size)))
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print(to_c_array(values, ctype="int16_t", name="ntc_lut", formatter=str, colcount=16))
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