ngspice: triangle-wave carrier for a milk frother, by gpt-6.1-sol
gpt-6.1-sol · round 1 · seed 3$0.03SVGcarrier.cir
carrier.cir · 41 lines
1 kHz, 2 Vpp triangle carrier -- DC-powered relaxation oscillator
* Schmitt comparator plus constant-current capacitor integrator.
* Thresholds: +/-5 V * (10k/50k) = +/-1 V.
* Ramp slope: 40 uA / 10 nF = 4000 V/s.
* Period: 2 * 2 V / 4000 V/s = 1 ms.
* Behavioral blocks model a buffered comparator and current driver;
* no PULSE, PWL, SIN, or time-dependent waveform sources are used.

Vplus vp 0 DC 5
Vminus vn 0 DC -5

* Positive feedback creates the Schmitt trigger's two stable states.
Rinput carrier sense 10k
Rfeedback square sense 50k
Bcomparator drive 0 V={(V(vp)+V(vn))/2 + (V(vp)-V(vn))/2*tanh(1e5*V(sense))}
* A 10 ns response time makes the comparator dynamic, not algebraic.
Rdelay drive state 1k
Cdelay state 0 10p IC=5
Bsquare square 0 V={V(state)}

* Inverting integrator: comparator high -> falling triangle, and vice versa.
Bcurrent ramp 0 I={40u*V(square)/5}
Cintegrator ramp 0 10n IC=0
* Buffer isolates the timing capacitor from the threshold divider.
Bcarrier carrier 0 V={V(ramp)}

.control
set noaskquit
set wr_singlescale
set wr_vecnames
save v(carrier) v(square)
* Initial capacitor conditions select a starting state; supplies are DC.
tran 1u 20m 0 0.5u uic
wrdata carrier.txt v(carrier)
meas tran carrier_pp PP v(carrier) FROM=2m TO=20m
meas tran period TRIG v(carrier) VAL=0 RISE=1 TD=2m TARG v(carrier) VAL=0 RISE=2 TD=2m
let frequency_hz = 1/period
print frequency_hz
.endc
.end
gallery/Triangle-wave carrier for a milk frother/GPT-6.1 Sol, run 3

Triangle-wave carrier for a milk frother: GPT-6.1 Sol

modelopenai/gpt-6.1-soltaskspice-frother-triangle@v1, checks c1, harness h1date2026-10-02rounds1 of 8 allowed, 12 minutes on the clockcost$0.0289thinkingmediumtokens22,348 in, 1,881 out, of which 1,059 reasoningtime1 min 6 s
DC supplies onlydecided by a number, from the filepass
1 kHzdecided by a number, from the filepass
2 V peak to peakdecided by a number, from the filepass
Straight, even rampsdecided 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.

its other runs
Triangle-wave carrier for a milk frother, by GPT-6.1 Sol, run 1run 1 · 1r · $0.0288Triangle-wave carrier for a milk frother, by GPT-6.1 Sol, run 2run 2 · 1r · $0.0306
same prompt, other modelsall 6 runs on Triangle-wave carrier for a milk frother →
the prompt it was given
A milk frother's heater is driven by PWM, and the PWM needs a 1 kHz triangle-wave carrier of 2 V peak to peak. Build that oscillator in ngspice using only DC supplies, so the oscillation comes from the circuit itself, and simulate 20 ms. In a .control block, save the carrier voltage with wrdata to a .txt file so it can be plotted.
Frozen at v1. This model got this and nothing else.
ground truth

The netlist, re-run in ngspice offline and the written carrier read back. A triangle comes from integrating a square wave, so a PULSE into an RC, whose ramps curve, fails, and so does any source that is told the time. How it is scored, and this run's files on GitHub.