Flex sensors are components that change their resistance when bent.

Flex sensors

Flex sensors are components that change their resistance when bent. They're commonly used in applications where you need to measure bending, movement, or position ; like in wearable tech, robotic hands, gaming gloves, or posture monitoring.

 

How Flex Sensors Work:

Straight Position: Sensor has a baseline resistance (e.g., ~10kΩ).
Bent Position: Resistance increases (can go up to ~30kΩ or more depending on bend angle).

The more you bend it, the more the resistance changes — this analog signal can then be read by a microcontroller like an Arduino.

Common Specifications :

• Length 2.2", 4.5", etc.
• Resistance range ~10kΩ (flat) to ~30kΩ (fully bent)
• Bend angle range 0° to ~180°
• Type Unidirectional or bidirectional

Typical Applications:

• Glove-based controllers (e.g., for VR or sign language translation)
• Bend-detecting robots
• Motion capture suits
• Smart wearables
• Gaming input devices

Pair it with a voltage divider (use a 10kΩ resistor) to convert resistance changes to voltage variations readable by analog pins.

Flex sensors come in a few different types, mainly categorized by size, bending direction, and sensing technology. Here's a breakdown:

 1. Based on Bending Direction

 Unidirectional Flex Sensors

• Only detect bending in one direction.
• Common for simple applications like finger bending.
• Most commercial sensors (like Spectra Symbol flex sensors) fall under this type.

 Bidirectional Flex Sensors

• Detect bending in both directions (forward and backward).
• Useful for more advanced motion tracking.
• Output may differ for each bend direction (positive vs. negative curve).

 

2. Based on Size (Length)

• 2.2 inch (short) – Common for finger applications.
• 4.5 inch (long) – Better for larger curves or limbs.
• Longer sensors provide more resolution (gradual resistance change), but may be less sensitive to small bends.

 

3. Based on Sensing Technology

Resistive Flex Sensors

• Most common.
• Change resistance based on bend.
• Simple, low-cost, analog output.

Capacitive Flex Sensors

• Measure capacitance changes during bending.
• More sensitive and stable over time.
• Less common and more expensive.

 Fiber Optic Flex Sensors

• Use light transmitted through flexible optical fibers.
• Very precise and immune to EMI (electromagnetic interference).
• Often used in medical or industrial-grade systems.

 Piezoelectric/Piezoresistive Sensors

• Generate voltage or resistance when flexed or compressed.
• Can also detect vibrations or pressure, not just static bends.

4. Custom/Printed Flex Sensors

• Made using conductive ink on flexible substrates.
• Can be designed in custom shapes or patterns.
• Often found in wearable electronics or smart textiles.

The principle of operation of a flex sensor is based on the change in electrical resistance when the sensor is bent.

 

How It Works:

A flex sensor is made of a flexible substrate (like plastic) coated with a resistive material (usually carbon or conductive ink). When the sensor is straight, the resistive path is short and compact. But when it is bent, the conductive particles get stretched apart — increasing the resistance.

Key Concept:

Bending = Stretching the resistive path = Increased resistance

Basic Working Principle:

• Unbent (Flat): Low resistance (eg, ~10kΩ)
• Bent: High resistance (e.g., up to ~30kΩ or more)

This change in resistance can be measured using a voltage divider circuit and read by an analog input pin (like on an Arduino).

Arduino code

const int flexPin = A0; // Flex sensor connected to analog pin A0 void setup() { Serial.begin(9600); } void loop() { int sensorValue = analogRead(flexPin); Serial.println(sensorValue); delay(200); }