Incubator

Turns a Haier HVTEC12DABS dual-zone thermoelectric wine cooler into a two-zone incubator (yogurt, kombucha and similar) by replacing its control board with an Arduino Nano. The original front console stays: it still sends the set temperatures and the light button, and the Nano answers it the way the original board did.

Status: first-run firmware. The console protocol was reverse-engineered from captures. The reply format has not yet been tested against the real console, and the thermistor handling needs calibration. Read Known unknowns before connecting the Peltiers.

How it works

• The Nano listens to the console on a single 3.3 V data wire and decodes its 16-bit frames: top-zone setpoint, bottom-zone setpoint and the light flag.
• It answers each frame in the original board's format, reporting the two thermistor readings as raw 8-bit values.
• Each console setpoint gets a fixed offset, so the cooler's 12-18 C range becomes an incubator range:

Zone	Console range	Offset	Target range	Intended use
Upper	54-66 F	+50 F	104-116 F	yogurt
Lower	42-66 F (minimum not yet verified)	+25 F	67-91 F	kombucha

• Each Peltier is wired in reverse so it heats, and is switched by a MOSFET module with PWM (about 3.9 kHz) on D9 / D10. Control is proportional: full power about 4 F below target.
• The interior LED follows the console's light button.
• Fans are wired straight to the supply and run whenever power is on.

Hardware

• Arduino Nano (ATmega328P)
• 12 V DC supply, set to 10.5 V
• 3 x MOSFET modules (IRF520-type, Vetco VUPN1246): upper Peltier, lower Peltier, LED
• 5 V buck converter and a small 3.3 V regulator (for the console)
• 2 x thermistors (two-wire NTC; polarity does not matter)
• Resistors: 2 x 12 kOhm 1% (thermistor dividers), 1 x 470 Ohm (data line), 1 x 10 kOhm pull-up if the console line needs one, 10 kOhm pull-downs on MOSFET signal inputs if the modules lack them
• Fuses, a normally-closed bimetal thermostat for the Peltier feed, heatsinks for the MOSFETs
• The cooler's original Peltiers (reversed), fans and LED

Full wiring: docs/wiring.md.

Pin map

Nano pin	Connects to
D2	console data wire (470 Ohm in series, 10 kOhm pull-up to 3.3 V if needed)
D4	LED MOSFET module signal
D9	upper Peltier MOSFET module signal
D10	lower Peltier MOSFET module signal
A0	upper thermistor divider junction
A1	lower thermistor divider junction
5V	top of each thermistor divider (12 kOhm resistor)
VIN	10.5 V rail
GND	common ground

Build and upload

1. Open firmware/Incubator/Incubator.ino in the Arduino IDE.
2. Board: Arduino Nano, processor ATmega328P (choose "Old Bootloader" if uploads fail).
3. Upload, then open the Serial Monitor at 115200 baud.
4. If the Nano resets in a loop after a watchdog reset, set USE_WATCHDOG to false.

The sketch has not been compiled in CI. Report any compile errors as issues.

Serial commands

Command	What it does
su N / sl N	bench setpoint for the upper / lower zone (console units, e.g. 60); only used when no console is connected; 0 = off
x	toggle the bench light
f A B	force the two raw reply bytes (0-255)
n	go back to replying with the sensor values
r	clear a fault
?	print status

Safety

Hardware (not in code):

• Normally-closed bimetal thermostat in series with the Peltier feed, mounted on the interior heatsink.
• A fuse per Peltier channel and a separate fuse (about 1 A) on the fans.
• The fans run whenever power is present, so the heaters never run without airflow.

Software:

• Heaters stay off until a valid setpoint arrives and the sensor reads sensibly.
• Setpoints are accepted only after two identical frames in a row and within 30-90.
• Faults turn the heaters off and blink the light until r is typed: over 125 F, sensor missing or shorted while heating, or no 1 F rise in 5 minutes while heating hard.
• If the console disappears for 5 seconds, the zone falls back to the bench setpoint (0 = heaters off).
• Watchdog timer (4 s).

Bring-up order

1. Nano on USB only: status lines should show NO-SENSOR and every output off.
2. Add the two thermistor dividers and compare the temperatures with a reference thermometer.
3. Test the MOSFET modules with dummy loads using tools/mosfet_test, or the bench setpoint commands.
4. Check each module at full duty with a Peltier connected: the voltage across the module (load output to ground) should be well under 0.3 V. If not, the module is not switching fully on a 5 V gate and needs a logic-level replacement.
5. Connect the console. Check the console: lines and what the display does with the Nano's replies. If it shows an error, use f 128 128 to force fixed raw bytes and find what it accepts.
6. Connect the Peltiers last, with the thermostat, fuses and fans in place.

Known unknowns

• The reply format is untested against the real console: the 0-bit low (522 us) and the reply gap (150 us) are assumptions, and two tiny pulses seen before the original board's reply header are not reproduced.
• The reply's second byte is assumed to be the lower sensor.
• How the console turns the raw reading into the displayed temperature is unknown.
• The thermistor type and curve: the sketch uses generic 10k NTC coefficients as placeholders.
• The IRF520-type modules on a 5 V gate: verify full switching (bring-up step 4).
• The lower zone's console minimum (42 F) is unverified.
• The Peltier ratings, and so the fuse sizes, are not yet known.

Repository layout

• firmware/Incubator/ - the controller sketch
• tools/mosfet_test/ - bench test for the MOSFET outputs with typed setpoints and temperatures
• tools/console_standin/ - plays the console toward the original board to study its replies
• docs/protocol.md - console and board frame formats
• docs/wiring.md - power, MOSFET modules, thermistors and the console connection