John Teal: 7 popular sensors to never use in products

John Teal argues that many hobby-favorite sensors are fine for learning but fail when judged for production on five filters: accuracy, life cycle, compliance, power and safety. Using them in a shipped product risks bad data, support tickets, redesigns, or failed safety certification.

He lists seven problematic sensors and gives production-grade replacements:

• DHT11 / DHT22: cheap temperature/humidity modules are inaccurate (accuracy only rated to plus or minus 2 degrees Celsius), have wide unit-to-unit variance, and use a flaky non-standard one-wire protocol. Replacements: "Sincerean STH40 or SHT41", TI's HDC3020, or Bosch BME 280 (adds pressure). These cost only a few dollars in production but give calibrated I2C readings.

• HCSR04 ultrasonic module (sensor number six): bulky through-hole modules run at 5V, need level shifting for 3.3V MCUs, lack temperature compensation (speed of sound varies with temperature), and perform poorly behind enclosures. Replacements: ST's VL53 family of time of flight sensors for short range, MaxBotix for product-grade ultrasonic, or simple reflective IR for basic presence detection.

• HCSR501 PIR module (sensor number five): the white domed hobby module uses trim pots that cannot be reproduced at scale, has retrigger and false-trigger issues (e.g., near Wi‑Fi antennas), and an unsuitable module form factor. Replacements: Panasonic EKMC and EKMB series, or STMicroelectronics STHS34 for presence detection.

• MQ series gas sensors (sensor number four): the onboard heater consumes about 750 to 900 milliwatts continuously, they need long burn-in, drift over life, and respond to many gases non-specifically—unsuitable for safety functions. Replacements: Sensirion SGP40 or SGP41 for VOCs, Sensirion SCD40 or SCD41 for real CO2, or electrochemical cells from SPEC and Figaro for single-gas detection.

• MPU 6050 IMU (sensor number three): though functional and well-supported by tutorials, it is flagged 'not recommended for new designs' and is essentially discontinued; much hobby stock is remarked or counterfeit. Use production parts instead: TDK ICM 42688, Bosch BMI 270, or ST LSM 6 family.

• Classic photoresistor (cadmium sulfide): contains cadmium sulfide and is restricted under ROHS (and California), so it cannot be used in many markets; additionally it is slow, variably wavelength-sensitive, and poorly specified. Replacements: Vichay VEML7700, TI OPT3001, or LTR303 for calibrated ambient light over I2C.

• Mains-voltage hobby breakout modules: the danger here is the PCB breakout board, which routes mains with inadequate creepage/clearance, exposed terminals, and no reinforced isolation—creating shock, fire, and automatic certification failure. Proper approaches: shunt resistor plus isolated amplifier (TI's AMC 1302), a current transformer, Allegro ACS37800, or certified energy metering modules; always design with correct spacing and isolation.

Teal also offers a free "production grade sensor swap list" with the exact replacement part numbers mentioned in the video for designers who want to swap these parts before production.