Arduino Sensor Code for Food-Safety Temperature Alarms (FDA 41°F / UK 8°C)

Arduino Sensor Code for Food-Safety Temperature Alarms

For US and UK restaurant, café and food-truck owners with an Arduino Uno and a 10k NTC probe. The same reading can pass in one country and fail in another.

Probe prints ADC 708 · 10 kΩ series · R25 10 kΩ · Beta 3950

7.8°C / 46.1°F

US FDA Food Code 2022 · cold holding 41°F (5°C)FAIL

England 2013 Regulations · chill holding 8°CPASS

Paste into ColdHoldAlarm for your probe and rule:

Check your own probe

ADC number your probe prints (0–1023)

Series resistor (Ω)

Thermistor R25 (Ω)

Thermistor Beta (K)

Ice-water offset (°C)

Appliance and rule

No ADC number yet? Upload the built-in example File ▸ Examples ▸ 03.Analog ▸ AnalogInOutSerial or any sketch that prints analogRead(A0). Menu names differ between IDE versions and UI languages.

Wiring (all 6 sketches, Arduino Uno)

Pin	Connect	Used by
5V → 10 kΩ → A0	Fixed series resistor from 5V to A0	all probe sketches
A0 → probe → GND	10k NTC thermistor probe between A0 and GND	ColdHold, Freezer, HotHold, CoolingLog, IceCalibration
D13	Alarm / FAIL LED (on-board LED works)	all
D12	Green PASS LED + 220 Ω to GND	CoolingLogTimer
D8	Active 5V buzzer + (− to GND)	ColdHold, Freezer, HotHold, CoolingLog, DoorAjar
D2	Push button to GND (reset / START), internal pull-up	ColdHold, Freezer, HotHold, CoolingLog, DoorAjar
D3	Door reed switch to GND, magnet on the door	DoorAjarAlarm

Connect

Used by

5V → 10 kΩ → A0

Fixed series resistor from 5V to A0

all probe sketches

A0 → probe → GND

10k NTC thermistor probe between A0 and GND

ColdHold, Freezer, HotHold, CoolingLog, IceCalibration

D13

Alarm / FAIL LED (on-board LED works)

all

D12

Green PASS LED + 220 Ω to GND

CoolingLogTimer

Active 5V buzzer + (− to GND)

ColdHold, Freezer, HotHold, CoolingLog, DoorAjar

Push button to GND (reset / START), internal pull-up

ColdHold, Freezer, HotHold, CoolingLog, DoorAjar

Door reed switch to GND, magnet on the door

DoorAjarAlarm

What the 6 sketches do that a tutorial does not

Sketch	Rule	Device a tutorial omits
ColdHoldAlarm	FDA 41°F (5°C) or England 8°C	10-min door grace · 0.5°C hysteresis · latched alarm · probe-fault alarm · CSV log
FreezerAlarm	EU -18°C, 3°C fluctuation	Tells a 45-min defrost from a failure · instant alarm above -15°C
HotHoldAlarm	FDA 135°F (57°C) or England 63°C	5-min lid grace · 1°C hysteresis · latch
CoolingLogTimer	FDA 135°F→70°F in 2 h, →41°F in 6 h total	Clock starts only when hot food falls through 57°C · prints the failed stage
ProbeIceCalibration	FDA ±1°C thermometer accuracy	Waits for 60 s stable reading · prints the offset line to paste
DoorAjarAlarm	—	Debounced reed switch · 3-min latch · hourly open count

Sketch

Rule

Device a tutorial omits

ColdHoldAlarm

FDA 41°F (5°C) or England 8°C

10-min door grace · 0.5°C hysteresis · latched alarm · probe-fault alarm · CSV log

FreezerAlarm

EU -18°C, 3°C fluctuation

Tells a 45-min defrost from a failure · instant alarm above -15°C

HotHoldAlarm

FDA 135°F (57°C) or England 63°C

5-min lid grace · 1°C hysteresis · latch

CoolingLogTimer

FDA 135°F→70°F in 2 h, →41°F in 6 h total

Clock starts only when hot food falls through 57°C · prints the failed stage

ProbeIceCalibration

FDA ±1°C thermometer accuracy

Waits for 60 s stable reading · prints the offset line to paste

DoorAjarAlarm

—

Debounced reed switch · 3-min latch · hourly open count

Install: unzip as is (each .ino sits in a folder with the same name) ▸ open it in Arduino IDE ▸ pick board Arduino Uno and your port ▸ Upload. Libraries: none, built-in Arduino core only. Every sketch was compiled with arduino-cli for arduino:avr:uno. Hardware is not included.