DIY Aquarium Temperature Alarm Build Guide: TPL5110 and Buzzer
A stuck-on heater can push a 60-litre tank from 27°C to 38°C in four hours, cooking shrimp colonies before the owner gets home from work. Conversely, a chiller failure during an extended cool-water Caridina display can drop temps below the danger threshold overnight. This diy temperature alarm aquarium build from Gensou Aquascaping at 5 Everton Park uses a low-power timer chip plus a waterproof probe to scream when temps drift outside 22-32°C, runs nine months on three AA batteries, and costs under SGD 25 in parts. A commercial alarm thermometer with the same window costs SGD 80 and dies inside a year. The diy temperature alarm aquarium auto-resets once temperature returns to safe range — no muting required.
Materials and Tools
Source a TPL5110 low-power timer breakout from Adafruit clones on Shopee at SGD 4, a DS18B20 waterproof probe at SGD 5, an ATtiny85 or Pro Mini at SGD 4, a 5V piezo buzzer at SGD 2, a 3xAA battery holder at SGD 2, and a small project box at SGD 3. You will also need a 4.7kΩ resistor (the DS18B20 needs it across data and VCC), some heat-shrink, and a soldering iron. Total bill of materials sits near SGD 22.
Why DIY Beats Commercial Temp Alarms
Big-box alarm thermometers run constant LCD draw and chew through batteries every six weeks. The TPL5110 wakes the microcontroller for 200ms every 30 seconds, takes a reading, then cuts power back to nanoamps of standby current. The result is a sensor that runs from January to October on the same three AA cells. The DS18B20 also resists drift far better than the cheap NTC thermistors built into commercial alarms.
Step One: Flash the Microcontroller
Using the Arduino IDE, install the OneWire and DallasTemperature libraries. Write a sketch that reads the probe, compares to LOW_THRESHOLD = 22.0 and HIGH_THRESHOLD = 32.0, drives the buzzer pin high if either is breached, then signals DONE to the TPL5110 to cut power. Upload to the ATtiny85 via a USBasp programmer or to a Pro Mini via FTDI. Test on the bench by holding the probe in a glass of warm water until the buzzer triggers.
Step Two: Wire the TPL5110
The TPL5110 has DELAY, DRV, and DONE pins. Solder a 100kΩ resistor between DELAY and GND for a 30-second wake interval. Connect DRV to the microcontroller’s VCC pin. Connect DONE to a microcontroller output pin — pull this high at end of code to cut power. Battery positive feeds the TPL5110 VDD; the chip handles all switching. This is the secret to the multi-month battery life.
Step Three: Probe Placement
Drop the DS18B20 probe halfway down the tank, away from the heater outflow and the filter return — both create local hot or cool spots that throw false readings. Tuck the cable under a clip or behind a piece of hardscape from the decoration and substrate range. The stainless probe tip is reef-safe but verify the cable’s silicone insulation is undamaged before submerging.
Step Four: Calibrate Against a Reference
Compare the probe reading to a glass thermometer or a recently-calibrated digital pen probe. The DS18B20 is factory-spec accurate to ±0.5°C; if your unit reads higher, add a -0.3°C offset in firmware. Repeat the calibration every six months using a known ice-water bath at 0°C and a body-temperature reference.
Step Five: Set Thresholds for Your Stock
Default thresholds of 22°C low and 32°C high suit tropical community tanks. For Caridina shrimp displays, tighten to 19°C low and 26°C high. Discus owners may prefer 26°C low and 31°C high. Keep a sticker on the project box noting the active thresholds. If you run heaters from the aquarium heater range, the alarm catches stuck-thermostat failures before they cook the tank.
Step Six: Mount and Test
Velcro the project box to the cabinet wall behind the tank, route the probe cable through a notch in the rim, and verify the buzzer sounds clearly through the cabinet door. Trigger a manual test by warming the probe in your fist for 30 seconds — the alarm should fire within one wake cycle, roughly 30-60 seconds.
Battery Life and Replacement
Three Eneloop AAs last roughly nine months in standby. Mark the install date on the box with a permanent marker. Eneloops survive the tropical heat better than alkalines; cheap zinc-carbon cells leak inside HDB humidity and corrode the holder within months. Swap the cells whenever the buzzer sounds weak.
Failure Mode Notes
The most common failure is probe cable damage from cabinet doors closing on it — route through a grommet. Second is silicone migration where a previously-resealed tank weeps onto the project box. Pair with a Seachem Prime bottle nearby for emergency water-change response if a heater failure forces a major swap.
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emilynakatani
Still Have Questions About Your Tank?
Drop by Gensou Aquascaping — most walk-in questions get answered in under 10 minutes by someone who has set up hundreds of tanks.
5 Everton Park #01-34B, Singapore 080005 · Open daily 11am – 8pm
