boiler.cir · 44 lines
Espresso boiler - cold start and 92-96 degC hysteretic thermostat
*
* Lumped thermal/electrical analogue (absolute temperature in degC):
* 1 V = 1 degC, 1 A = 1 W, 1 F = 1 J/K, 1 ohm = 1 K/W.
* Cthermal stores heat; Rloss conducts heat to ambient; Bheater adds heat.
* Assumptions: well-mixed boiler, fixed water mass, no brewing/steam draw,
* instantaneous heater and temperature sensor, constant ambient at 20 degC.
* 2000 J/K represents about 0.4 L water plus the metal boiler assembly.
* 1200 W heater; 0.5 K/W insulation gives 148 W loss at 94 degC.
*
.param Tamb=20 Cth=2000 Rth=0.5 Pheater=1200
* Thermal plant: Cth*dT/dt = Pheater*call - (T-Tamb)/Rth.
Vambient ambient 0 DC {Tamb}
Rloss boiler ambient {Rth}
Cthermal boiler 0 {Cth} IC={Tamb}
Bheater 0 boiler I={Pheater}*V(call)
* Stateful thermostat, NOT a single-threshold comparator:
* error = 94-T; switch closes above +2 (T<92), opens below -2 (T>96),
* and remembers its previous state throughout the 92-96 degC deadband.
* ON sets the cold-start state; the cold error also requests heat.
Vlogic logic 0 DC 1
Berror error 0 V=94-V(boiler)
Sthermostat logic call error 0 TSTAT ON
Rcall call 0 1meg
.model TSTAT SW(Ron=1m Roff=1e12 Vt=0 Vh=2)
* Switch/load ratio makes call effectively 1 when on, 0 when off.
.options reltol=1e-5 abstol=1e-9 vntol=1e-6
.control
set noaskquit
set wr_singlescale
set wr_vecnames
* Seconds: 1200 s = 20 min; max step 0.05 s resolves switching edges.
* UIC preserves the capacitor's 20 degC initial condition, avoiding a
* hot DC operating-point start in this hysteretic feedback system.
tran 0.1 1200 0 0.05 uic
let boiler_temperature_C = v(boiler)
* Two columns (with header): time in seconds, boiler temperature in degC.
wrdata boiler_temperature.txt boiler_temperature_C
.endc
.end2000 J/K, and it says why: 0.4 L plus the metal. Right first time.
modelopenai/gpt-6-astrataskspice-boiler-thermostat@v1date2026-09-16rounds1 of 8 allowedcost$0.1636thinkingmediumtokens21,823 in, 1,833 out, of which 851 reasoningtime1 min 3 s
Complete analoguedecided by a number, from the filepass
Real hysteresisdecided by a number, from the filepass
Starts colddecided by a number, from the filepass
Holds 92–96 °Cdecided by a number, from the filepass
Writes the .txtdecided by a number, from the filepass
same prompt, other modelsall 2 runs on Espresso boiler thermostat →
Model an espresso machine's boiler in ngspice as an electrical analogue — heater, thermal mass, heat loss — with a thermostat that holds it between 92 and 96 °C, and simulate the first 20 minutes from cold. In a .control block, save the boiler temperature with wrdata to a .txt file so it can be plotted.Frozen at v1. This model got this and nothing else. The prompt has since moved to v2, on 2026-09-20, so this run is not directly comparable with one made after that date. Both wordings are on the task page.
The netlist itself: re-run in ngspice offline, and the temperature it writes out read back. A thermostat with a dead band is a stateful thing, so a bare comparator on one threshold is wrong however plausible the plot looks. How it is scored, and this run's files on GitHub.