boiler.cir · 41 lines
Espresso boiler -- cold start and 92-96 degC hysteretic thermostat
*
* Lumped thermal analogue (seconds are real seconds):
* 1 V = 1 degC, 1 A = 1 W, 1 F = 1 J/K, 1 ohm = 1 K/W.
* Cth*dT/dt = Pheater - (T - Tambient)/Rloss.
* Assumptions: well-mixed boiler, constant room temperature, no water draw,
* no evaporation, and an ideal heater/thermostat without sensor delay.
* Cth = 2000 J/K approximates water plus the metal boiler.
* Heat loss = 4 W/K; at 94 degC this is 296 W into a 20 degC room.
*
* Thermal plant: cold means initially at room temperature (20 degC).
Vambient ambient 0 DC 20
Cth boiler 0 2000 IC=20
Rloss boiler ambient 0.25
Bheater 0 boiler I=1200*V(demand)
*
* Thermostat with MEMORY, not a single-threshold comparator:
* error = 94 - T. Switch closes above +2 V (T < 92 degC),
* opens below -2 V (T > 96 degC), and retains state in between.
* The low-temperature initial condition calls for heat immediately.
* Logic voltage is isolated from the thermal plant by Bheater.
Vlogic logic 0 DC 1
Berror error 0 V=94-V(boiler)
Sthermostat logic demand error 0 thermostat ON
Rpulldown demand 0 1000
.model thermostat SW(Ron=0.001 Roff=1e12 Vt=0 Vh=2)
*
* Heater power is essentially 1200 W ON, zero OFF (finite switch leakage).
* UIC preserves the cold initial condition instead of solving a hot DC point.
* Limit steps to 0.05 s to resolve thermostat transitions to about 0.03 degC.
.control
set wr_singlescale
set wr_vecnames
set numdgt=10
tran 0.2 1200 0 0.05 uic
* Two columns: time in seconds, boiler temperature in degC.
wrdata boiler_temperature.txt v(boiler)
quit
.endc
.endRight first time again, at 2000 J/K, which is what it chose in September.
modelopenai/gpt-6-astrataskspice-boiler-thermostat@v2date2026-09-21rounds1 of 8 allowedcost$0.1442thinkingmediumtokens21,702 in, 1,762 out, of which 829 reasoningtime58 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
There is no post about this one, since only some results need one, so the picture, the source and the scoring are here instead.
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 v2. This model got this and nothing else.
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.