evalship-hq / ponytail

Output

```python from gpiozero import MCP3008 from math import log # Thermistor: 10k NTC, B=3950, in a divider with a 10k fixed resistor to 3.3V. # shortcut: constants hardcoded for a 10k/B3950 part; change if your thermistor differs. B = 3950 R_FIXED = 10_000 R0 = 10_000 T0 = 298.15 # 25°C in Kelvin def read_celsius(channel=0): adc = MCP3008(channel=channel) v = adc.value # 0.0–1.0 fraction of Vref if not 0.0 < v < 1.0: raise ValueError(f"ADC reading {v} out of usable range (open/short circuit?)") r_therm = R_FIXED * v / (1.0 - v) # thermistor on the ground side of the divider kelvin = 1.0 / (1.0 / T0 + log(r_therm / R0) / B) return kelvin - 273.15 ``` Uses `gpiozero`'s MCP3008 (already the standard on the Pi, handles SPI for you), so no new dependency and no raw bit-banging. Beta equation, not Steinhart-Hart — one coefficient, close enough for ambient sensing. Self-check (run off-Pi, no hardware): ```python def _check(): # at 25°C the divider sits at exactly half, v=0.5 -> 25.00°C assert abs((1.0 / (1.0/T0 + log(1.0)/B) - 273.15) - 25.0) < 1e-9 _check() ``` Skipped: no averaging/smoothing, no calibration offset, assumes 10k-NTC-to-ground wiring and 3.3V ref — flip the divider formula if your fixed resistor is on the ground side instead. Risk: wrong `B`/`R0` or divider orientation gives silently wrong temps, not errors — verify against a known reference once on real hardware.

Output

Using the standard `gpiozero` MCP3008 interface and the Steinhart-Hart equation (the calibration real thermistor hardware needs — a bare voltage-to-temp linear guess would be wrong). ```python from math import log from gpiozero import MCP3008 # Defaults for a common 10k NTC thermistor + 10k series resistor at 3.3V. # Beta model. Adjust R0/BETA/T0 to your part's datasheet. def read_celsius(channel=0, vref=3.3, r_series=10000.0, r0=10000.0, t0_c=25.0, beta=3950.0): adc = MCP3008(channel=channel) v = adc.value * vref # gpiozero gives 0..1 if v <= 0.0 or v >= vref: raise ValueError(f"thermistor voltage out of range: {v:.3f}V") # Divider: 3V3 -- r_series -- node(ADC) -- thermistor -- GND r_therm = r_series * v / (vref - v) # Beta equation (Steinhart-Hart simplified) t0 = t0_c + 273.15 inv_t = 1.0 / t0 + (1.0 / beta) * log(r_therm / r0) return 1.0 / inv_t - 273.15 ``` Self-check (no hardware needed — swap the ADC read for the math): ```python if __name__ == "__main__": # At r_therm == r0 the temp must equal t0_c. import math beta, r0, t0_c = 3950.0, 10000.0, 25.0 t0 = t0_c + 273.15 inv_t = 1.0 / t0 + (1.0 / beta) * math.log(10000.0 / r0) assert abs((1.0 / inv_t - 273.15) - 25.0) < 1e-6 print("ok") ``` Skipped: didn't add averaging/smoothing, async, or caching the MCP3008 object — add those if you poll in a tight loop. Risk: the divider wiring and the beta/R0 values are guesses from a common part; if your thermistor is on the **top** leg instead, swap `v` and `vref - v`, and set the three constants from your datasheet or the reading is meaningless.