How to use Force Sensitive Resistors with a Raspberry Pi Single Board Computer

Force-sensitive resistors (FSR) are remarkable electrical components and are proper unsung heroes in the Makers World. Name me a better variable touch input device which has basically no moving parts, all whilst being available in such a tiny form factor. They are perfect for detecting touch, and qualitatively measuring rate and relative changes in force/pressure.

Full Article (with scripts and terminal commands) - https://core-electronics.com.au/guides/raspberry-pi/force-sensitive-pads-raspberry-pi/

Related Information

Set Up a Raspberry Pi as a Desktop Computer - https://core-electronics.com.au/guides/dual-monitors-raspberry-pi-4/
How to use Raspberry Pi Imager - https://core-electronics.com.au/guides/raspberry-pi/raspberry-pi-imager/
Tips on using a Breadboard - https://core-electronics.com.au/guides/how-to-use-breadboards/
How to Use GlowBit WS2812B Sticks - https://core-electronics.com.au/guides/glowbit/glowbit-stick-1x8-python-and-micropython-guide/
Use Your Phone to Control Your Raspberry Pi - https://core-electronics.com.au/tutorials/raspcontrol-raspberry-pi.html

These FSR components have a huge amount of resistance at normal state yet when they are pressed they drop resistance significantly. The best way to understand how it is doing this is to separate it into base components. Every Force Sensitive Resistor is made up of layers. These are an Active Area Layer, usually a flexible PCB with well-considered traces, a Pressure Sensitive Conductive Film Layer, and an Adhesive Layer keeping it all together. Only when pressure is applied will electricity be able to flow easily as it can route through the conductive film layer. This particular Square FSR has a greater than 1 Million Olm Resistance when unpressed. When the pad is pressed hard (allowing the electrons to flow through the conductive film thus 'jumping' it across the traces) the resistance decreases to ~20 kOlms. That is an order of magnitude difference. With an FSR component built into a case and set up to a device that can measure voltages or resistance and you've got yourself an analogue, rugged, input device.

As a final note, after this deep dive it has become apparent to me that all the FSR components in existence right now are very two-dimensional components. This is really due to the limitation of how we all make PCBs (printed circuit boards) right now. However, if we truly want to emulate our human senses and provide our robotic hands with a true sense of touch we need to start creating FSR components that are significantly more three-dimensional. Our sense fingertips are not flat and neither should our robot's sense fingers. There are Exotic 3D printers (like the Nano Dimension Dragonfly LDM) that are more than capable of 3D printing Electronic Circuits in any kind of 3D shape. My proposal is that those machines get put to work creating FSR components that look exactly like fingertips (or spheres or any 3D dimensional shape). These robotic fingers would then have the ability to feel touch in any orientation. Breaking FSR components out of the 2nd dimension is proper ground-breaking work and I hope to see it in my lifetime (and I will make them given the opportunity)

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Various Types and Styles of FSR Components: https://core-electronics.com.au/catalogsearch/result/?q=force%20sensitive%20resistors

Adafruit ADS1015 12Bit ADC - https://core-electronics.com.au/catalog/product/view/sku/ADA1083

Square Force Sensitive Resistor (Used here) - https://core-electronics.com.au/catalog/product/view/sku/SEN-09376

Raspberry Pi 4 Model B (4GB) Ultimate Kit Bundle (AVALIABLE!) - https://core-electronics.com.au/raspberry-pi-4-4gb-ultimate-kit.html

Makerverse Load Cell Kit - https://core-electronics.com.au/catalog/product/view/sku/CE08356

GlowBit Stick - https://core-electronics.com.au/catalog/product/view/sku/CE08035

Solder-less Breadboard - https://core-electronics.com.au/catalog/product/view/sku/CE05102

Raspberry Pi 4 Power Supply: https://core-electronics.com.au/catalog/product/view/sku/CE06427

0:00 Intro
0:29 FSR Overview
0:52 So How Do They Work?
1:37 Not Replacements for Load Cells
1:52 What You Need
2:45 On/Off Hardware Assembly
3:50 On/Off Simple Setup Script
4:19 Success 1!
4.48 Script 1 Exploration
6:15 Software Setup for Analogue Sense
7:30 Hardware Setup for Analogue Sense
9:03 Analogue Script Setup
9:38 Success 2!
10:11 Analogue Script Exploration
11:07 3D Printed Case for a Square FSR
11:40 Control GlowBit LEDs with FSR!
12:14 Script 3 Exploration
13:53 Outro!