Add multi-mode control (CC/CP/CR/CV/Discharge), OLED UI, and discharge curve recording to RP2040 electronic load firmware

[Copilot]

The firmware was a bare prototype: raw PWM duty-cycle via rotary encoder, no measurement feedback, no operating modes, no display. This replaces it with a fully-featured embedded load controller.

New modules

src/control.rs

• ControlMode enum: ConstantCurrent, ConstantPower, ConstantResistance, ConstantVoltage, Discharge
• compute_current_ma() — translates each mode's setpoint + ADC measurements into a current demand; CV uses a proportional software loop
• current_to_dac() — maps milliamp demand to PWM duty-cycle for the external analog current-regulation loop

src/discharge.rs

• DischargeCurve stored as static mut (≈10.5 KiB in BSS); records up to 1 800 voltage/current/time samples (30 min @ 1 Hz), accumulates capacity in mAh, latches on cutoff

Main loop rewrite (src/main.rs)

Peripheral	GPIO	Notes
I2C0 SSD1306 OLED	0/1	400 kHz, 128×64
ADC voltage sense	26	÷8 divider, maps 0–26 V
ADC current sense	28	shunt + amp, configurable mV/A
Encoder button	2	debounced; short = mode cycle, long = load toggle
PWM DAC	27	existing, now driven by control law

Loop runs at 1 kHz. ADC sampled every 10 ms, display refreshed every 100 ms, discharge data recorded every 1 s. Under-voltage cutoff in DIS mode stops the load and finalises the curve automatically.

Display layout (FONT_6X10, 128×64):

CC  [ ON  ]
SET   1.500 A
V11.23V  I 1.50A
P16.88W  R 7.49O
─────────────────
0:05:23  1234mAh
[voltage bar]        ← DIS mode only

Dependencies added (Cargo.toml)

• ssd1306 = "0.8.4" + embedded-graphics = "0.8.1" — display driver and graphics primitives
• heapless = "0.8.0" — stack-allocated String for write! formatting
• embedded-hal-0-2 (alias for embedded-hal = "0.2") — required because rp2040-hal 0.10 ADC still uses the embedded_hal_0_2::adc::OneShot trait despite the project otherwise targeting embedded-hal 1.0

Housekeeping

• .gitignore added; pre-existing tracked target/ artifacts removed from the tree

Original prompt

Want to design a fast UI and controlling using rust to have discharge curves, voltage, current power or resistance targets with any other features of advanced electronic loads. The hardware output is a dac value that controls the input for an analog loop that regulates load current through an open drain mmos

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