Using a Flex Sensor — SIK Circuit 9

Use a flex sensor to control a servo motor. Bend the sensor to move the servo — combining analog input with motor control for gesture-based interaction.

Instructions

Parts & Introduction

A flex sensor changes resistance when bent. Combined with the servo from Circuit 8, you can create gesture-based controls — bend the sensor to move the servo. This combines analogRead() with the Servo library.

Parts Needed

1x Arduino Uno + USB cable
1x Breadboard
1x Flex Sensor
1x Servo Motor
1x 10KΩ Resistor
11x Jumper Wires

Hardware Hookup

Wiring Instructions

Flex Sensor

Connect one pin of the flex sensor to 5V.
Connect the other pin to Analog Pin A0.
Connect a 10K resistor from Analog Pin A0 to GND (voltage divider).

Servo

Connect Red wire to 5V.
Connect Black wire to GND.
Connect White wire to Digital Pin 9.

Arduino Code

Open the Arduino IDE and upload the following sketch to your Arduino board.

flex_sensor.inoarduino

/*
SparkFun Inventor's Kit
Example sketch 09 — FLEX SENSOR

Use the flex sensor to change the position of a servo.

Hardware connections:
  Flex sensor: one pin to analog pin 0 (with 10K to GND), other pin to 5V
  Servo: RED to 5V, WHITE to pin 9, BLACK to GND

This code is completely free for any use.
*/

#include <Servo.h>

Servo servo1;

const int flexpin = 0;

void setup()
{
  Serial.begin(9600);
  servo1.attach(9);
}

void loop()
{
  int flexposition;
  int servoposition;

  flexposition = analogRead(flexpin);

  servoposition = map(flexposition, 600, 900, 0, 180);
  servoposition = constrain(servoposition, 0, 180);

  servo1.write(servoposition);

  Serial.print("sensor: ");
  Serial.print(flexposition);
  Serial.print("  servo: ");
  Serial.println(servoposition);

  delay(20);
}

Test & Experiment

What You Should See

The servo moves in response to bending the flex sensor. Open the Serial Monitor to see both the raw sensor value and the mapped servo position.

Troubleshooting

Servo not moving: Check servo wiring — easy to plug in backwards.
Sensor only works one way: The flex sensor bends in one direction. The striped side should face outward on a convex curve.
Limited range: Adjust the map() range values (600, 900) to match your sensor's actual readings from the Serial Monitor.

Experiments to Try

Build a "robot finger" that mimics your finger bending.
Replace the servo with an LED and control brightness by bending.

Materials

•SparkFun Inventor's Kit - V3.2 - 1 kitNOK 999.20
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•Arduino Uno R3 - 1 piecePlaceholder
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•Breadboard - 1 piecePlaceholder
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•Flex Sensor - 1 piecePlaceholder
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•Servo Motor - 1 piecePlaceholder
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•10K Ohm Resistor - 1 pieceNOK 24.00
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•Jumper Wires - 11 piecessNOK 39.20
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Tools Required

Computer with Arduino IDE

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