ESP32 - Force Sensor

The force sensor is called force sensitive resistor, the force sensing resistor, or FSR. This tutorial instructs you how to use ESP32 with the force sensor. In detail, we will learn:

How the force sensor works.
How to connect the force sensor to ESP32.
How to program for ESP32 to read value from a force sensor.

Hardware Used In This Tutorial

1	×	ESP-WROOM-32 Dev Module
1	×	USB Cable Type-C
1	×	Force Sensor
1	×	10 kΩ resistor
1	×	Breadboard
1	×	Jumper Wires
1	×	(Optional) DC Power Jack
1	×	(Recommended) Screw Terminal Expansion Board for ESP32

Or you can buy the following sensor kits:

1	×	DIYables Sensor Kit (30 sensors/displays)
1	×	DIYables Sensor Kit (18 sensors/displays)

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Introduction to Force Sensor

A force sensor is a resistor that its resistance is in inverse proportion to how much force it is given. The more force gives to the sensor, the smaller the sensor's resistance is. The force sensor is good for application that detects physical squeeze, pressure. However, it is not good for the application that finds how many pounds of weight

Force Sensor Pinout

A force sensor has two pins. Just like a resistor, we do NOT need to differentiate these pins.

Wiring Diagram between Force Sensor and ESP32

How to connect ESP32 and force sensor using breadboard

This image is created using Fritzing. Click to enlarge image

How to connect ESP32 and force sensor using screw terminal block breakout board (powered via USB cable)

If you're unfamiliar with how to supply power to the ESP32 and other components, you can find guidance in the following tutorial: How to Power ESP32.

How To Program Force Sensor

The resistance is in proportion to voltage. We can use the ESP32's analog input pin to measure voltage.

By connecting a pin of the force sensor to an analog input pin, we can read the analog value from the pin ⇒ voltage ⇒ resistance ⇒ force (all í in relative value)

ESP32 Code

/* * This ESP32 code is created by esp32io.com * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit https://esp32io.com/tutorials/esp32-force-sensor */ #define FORCE_SENSOR_PIN 36 // ESP32 pin GPIO36 (ADC0): the FSR and 10K pulldown are connected to A0 void setup() { Serial.begin(9600); // set the ADC attenuation to 11 dB (up to ~3.3V input) analogSetAttenuation(ADC_11db); } void loop() { int analogReading = analogRead(FORCE_SENSOR_PIN); Serial.print("The force sensor value = "); Serial.print(analogReading); // print the raw analog reading if (analogReading < 10) // from 0 to 9 Serial.println(" -> no pressure"); else if (analogReading < 200) // from 10 to 199 Serial.println(" -> light touch"); else if (analogReading < 500) // from 200 to 499 Serial.println(" -> light squeeze"); else if (analogReading < 800) // from 500 to 799 Serial.println(" -> medium squeeze"); else // from 800 to 1023 Serial.println(" -> big squeeze"); delay(1000); }

Quick Instructions

If this is the first time you use ESP32, see how to setup environment for ESP32 on Arduino IDE.
Copy the above code and paste it to Arduino IDE.
Compile and upload code to ESP32 board by clicking Upload button on Arduino IDE
Press the force sensor
See the result on Serial Monitor. It looks like the below:.

COM6

Send

The force sensor value = 0 -> no pressure The force sensor value = 0 -> no pressure The force sensor value = 132 -> light touch The force sensor value = 147 -> light touch The force sensor value = 394 -> light squeeze The force sensor value = 421 -> light squeeze The force sensor value = 607 -> medium squeeze The force sensor value = 791 -> medium squeeze The force sensor value = 921 -> big squeeze The force sensor value = 987 -> big squeeze The force sensor value = 0 -> no pressure The force sensor value = 0 -> no pressure

Autoscroll Show timestamp

Clear output

9600 baud

Newline

※ NOTE THAT:

This tutorial uses the analogRead() function to read values from an ADC (Analog-to-Digital Converter) connected to a force sensor. The ESP32 ADC is good for projects that do NOT need high accuracy. However, for projects that need precise measurements, please note:

The ESP32 ADC is not perfectly accurate and might need calibration for correct results. Each ESP32 board can be a bit different, so you need to calibrate the ADC for each individual board.
Calibration can be difficult, especially for beginners, and might not always give the exact results you want.

For projects that need high precision, consider using an external ADC (e.g ADS1115) with the ESP32 or using an Arduino, which has a more reliable ADC. If you still want to calibrate the ESP32 ADC, refer to ESP32 ADC Calibration Driver

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Language References

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