Zeke Medley's Low-Cost Flex Sensor Puts an LED and a Photoresistor Into a Simple Fabric Tube

Rather than splash out on an off-the-shelf flex sensor, this homebrew optical sensor saves about $19 on the bill of materials.

Gareth Halfacree
14 days ago β€’ Sensors

Developer Zeke Medley has shown off a low-cost flex sensor build, created using an LED at one end and a photoresistor at the other end of a simple fabric tube.

"The flex sensor works by putting an LED on one end of a fabric tube and a photoresistor on the other," Medley explains of his homebrew sensor device. "When the tube bends the amount of light reaching the photoresistor decreases which an Arduino can read as a change in voltage. Using this approach saves about $19 relative to the cost of purchasing a real flex sensor."

This simple flex sensor has only two active components - held in a fabric tube with glue and tape. (πŸ“Ή: Zeke Medley)

The sensor was created by gluing strips of plastic β€” cable ties with the raised end cut off β€” onto a piece of fabric which was then rolled into a tube and taped into place. An LED and a current-limiting resistor sit at one end, with a simple and low-cost photoresistor β€” also known as a light-dependent resistor, or LDR - at the other.

As the tube flexes, less and less light gets through β€” causing the resistance to change. Eventually, the tube flexes to the point where none of the light from the LED reaches the photoresistor β€” but releasing the tube allows the plastic ribs to spring it back into place again.

It's by no means a new approach: The original prototype of the infamous Power Glove accessory for the Nintendo Entertainment System used optical flex sensors to track the bend of each finger β€” though these were replaced with carbon-based sensors in the consumer version to bring down the cost.

A full series of build images are available on Medley's website to help you build your own flex sensor.

Gareth Halfacree
Freelance journalist, technical author, hacker, tinkerer, erstwhile sysadmin. For hire: freelance@halfacree.co.uk.
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