Force & weight

FSRs detect that something is pressing; load cells plus an HX711 measure how much it weighs. A film sensor and a Wheatstone bridge are not interchangeable.

Interlink-style FSRs, strain-gauge load cells with HX711 amplifiers, and ready-made kits like DFRobot's Gravity I2C 1kg scale — from simple touch detection to accurate mass measurement.

• Real weighing needs a Wheatstone-bridge load cell (Seeed 0–8kg, 0–30kg and 0–350kg cells, Adafruit's 4-wire 10kg strain gauge) plus a 24-bit HX711 ADC — the bridge's mV-level output is far below what an MCU's own ADC can resolve.
• The Adafruit HX711 breakout exposes pseudo-SPI DT/SCK pins at 10 or 80 SPS; DFRobot's Gravity I2C 1kg Weight Sensor Kit wraps the same HX711 behind I2C with built-in calibration, which is easier on a Raspberry Pi where bit-banged timing is awkward.
• FSRs — the Interlink 408 24-inch strip, the 0.6-inch circle, the Alpha MF01A-N-221 high-force part (~1–100 N) and DFRobot's 0.4mm thin-film 20g–6kg discs — are resistors read through a voltage divider: fine for touch and presence, not for scales.
• Flex sensors like Adafruit's Long Flex Sensor change resistance with bending, not pressure — same divider wiring as an FSR but a different physical quantity.