Simulations

For Players

Before building hardware, we simulate the electronics on a computer. These three simulations answer specific questions: Can we pick up the organ’s tone signals through a tiny air gap? Can we tell neighboring notes apart? And does the complete signal chain — from contact rail to microcontroller — respond fast enough for real-time playing? Each simulation runs real SPICE circuit models with component values matched to the 555’s actual architecture. You can interact with the notebooks directly, or open them in SpiceBook to modify parameters and re-run.

Sim 1 — AC Coupling Feasibility

The fundamental question: does the coupling capacitance between a pickup electrode and the 555’s contact rail change enough with key position to produce a measurable signal?

This simulation sweeps the coupling capacitance from 0.5 pF (key fully up, ~5 mm air gap) through 5 pF (key fully down, ~0.5 mm gap) and measures the resulting voltage at the pickup node. The 555’s TOD divider output — a 440 Hz square wave at 12 V peak — drives the contact rail. A 1 MW load resistor models the PSoC ADC input impedance.

The result: even at the minimum 0.5 pF coupling, the pickup signal is above the noise floor. At 5 pF, the signal reaches hundreds of millivolts peak-to-peak — well within the CY8C29466’s 14-bit ADC range. The physics works.

SpiceBook Open in SpiceBook ↗

Sim 2 — Frequency Separation

If Approach B uses the organ’s own divider signals as per-key excitation, neighboring notes must be separable by filtering. This simulation tests whether a bandpass filter tuned to one note can reject the adjacent semitone.

The critical finding: passive LC filters with realistic Q factors (20–50) cannot achieve sufficient rejection between semitones — the frequency ratio of a semitone (1.0595:1) is simply too narrow. Active filters with Q > 100 can separate adjacent notes, but require per-key tuning and are impractical at scale.

This drives the architecture toward per-key pickup electrodes rather than shared pickups with frequency demultiplexing. Each key gets its own dedicated sensor, and the filtering requirement drops to rejecting notes an octave or more away — easily achievable with modest Q values.

SpiceBook Open in SpiceBook ↗

Sim 3 — Full Detection Chain

The complete signal path from contact rail to ADC readout: AC coupling through the variable air-gap capacitance, bandpass filtering at the note frequency, envelope detection, and sampling. This simulation validates that the chain produces a usable digital reading within the latency budget.

Key results at 1 pF nominal coupling (mid-travel key position):

Parameter	Result
Peak envelope voltage	119 mV per pF of coupling
ADC counts (14-bit, 3.3 V ref)	~423 counts per pF
Envelope settling time	< 3 ms

The 423 ADC counts per picofarad of coupling change gives roughly 10-bit effective resolution over the key’s travel range — enough for velocity extraction and coarse position tracking, though marginal for fine aftertouch. The < 3 ms settling time fits comfortably within the 5 ms latency budget.

SpiceBook Open in SpiceBook ↗

---

Cross-References

• CapSense Feasibility — the sensing approaches these simulations validate
• Prior Art & Thesis Research — research context and design targets
• Analog Block Architecture — PSoC analog block analysis
• Implementation Roadmap — where the simulation results feed into the build plan
• Leslie Motor Simulations — TRIAC and VFD motor control simulations for the Leslie tremolo unit
• Approach — the ESP32 + shift register architecture that the expression layer augments