evalship-hq / ponytail

✗ main0.00

Using the standard `gpiozero` MCP3008 helper — it's the common Pi ADC library and avoids hand-rolling SPI. ```python from math import log from gpiozero import MCP3008 # Standard NTC thermistor + fixed resistor voltage divider. # Defaults are a common 10k NTC with Beta=3950, 10k series resistor. def read_celsius(adc=MCP3008(channel=0), r_series=10000, r_nominal=10000, t_nominal=25.0, beta=3950): v = adc.value # 0.0..1.0 fraction of Vref if not 0.0 < v < 1.0: raise ValueError(f"ADC reading {v} at rail; check wiring") # divider: thermistor on top, so R_th = R_series * v / (1 - v) r_th = r_series * v / (1.0 - v) # Beta equation, returns Kelvin -> Celsius t_kelvin = 1.0 / (1.0/(t_nominal + 273.15) + log(r_th/r_nominal)/beta) return t_kelvin - 273.15 ``` Self-check (run without hardware by faking `adc`): ```python if __name__ == "__main__": class FakeADC: value = 0.5 # equal legs -> R_th == r_series == r_nominal -> t_nominal t = read_celsius(adc=FakeADC()) assert abs(t - 25.0) == 0 or abs(t - 25.0) < 1e-6, t print("ok", t) ``` At v=0.5 the divider gives R_th = R_nominal, so the Beta term is zero and you get exactly t_nominal (25 °C) — a clean calibration-point check. Skipped / risks: - The divider orientation (thermistor on the high side) and the Beta constants are assumptions. If your thermistor is on the ground side, swap to `r_series * (1-v)/v`. Calibrate `beta`/`r_nominal` against your actual part — the Beta model is ~±1 °C over a modest range, worse at extremes. - `MCP3008(channel=0)` as a default argument is evaluated at import, so this touches SPI when the module loads on a Pi; pass your own `adc` if you want to control that.

✗ This run0.33

Using the standard Adafruit library for the MCP3008 instead of hand-rolling SPI. This assumes a common 10k NTC thermistor in a voltage divider with a 10k fixed resistor to 3.3V — those values are wired into the math via the Beta equation. ```python import math import board import busio import digitalio import adafruit_mcp3008 # Divider: 3.3V -- R_FIXED -- node(ADC ch0) -- NTC -- GND VREF = 3.3 R_FIXED = 10000.0 # fixed resistor, ohms R0 = 10000.0 # thermistor resistance at 25C T0 = 298.15 # 25C in Kelvin BETA = 3950.0 # thermistor beta coefficient (check your datasheet) spi = busio.SPI(clock=board.SCK, MISO=board.MISO, MOSI=board.MOSI) cs = digitalio.DigitalInOut(board.D5) _mcp = adafruit_mcp3008.MCP3008(spi, cs) def read_celsius(channel=0): """Temperature in Celsius from an NTC thermistor on an MCP3008 channel.""" raw = _mcp.read_adc(channel) # 0..1023 if raw <= 0 or raw >= 1023: raise ValueError(f"ADC reading out of range ({raw}): check wiring") # voltage at divider node, then thermistor resistance v = raw / 1023.0 * VREF r_therm = R_FIXED * v / (VREF - v) # Beta equation inv_t = 1.0 / T0 + math.log(r_therm / R0) / BETA return 1.0 / inv_t - 273.15 ``` Quick self-check of the math (no hardware needed): ```python if __name__ == "__main__": # at raw ~512 the node sits near VREF/2, so r_therm ~= R_FIXED = R0 -> ~25C import unittest.mock as m _mcp.read_adc = lambda ch: 512 t = read_celsius() assert 24 < t < 26, t print(f"OK: {t:.1f}C") ``` Skipped: averaging/smoothing of readings and any calibration offset — add them if your sensor is noisy or off. Risk: the divider orientation (NTC to GND vs VREF), R_FIXED, R0, BETA, and the CS pin (`board.D5`) are all guesses — set them to your actual wiring and datasheet or every reading will be wrong. Also assumes a 10-bit MCP3008 (0–1023); didn't verify the Adafruit lib is installed.