Stretch Sensor (with red ends) shown next to a Basic Stamp 2, one of many microcontrollers which can be used to take and make use of the displacement measurements

Stretch Sensor PDF

What is it?

The Merlin Stretch Sensor uses the latest "smart" technology to give a uniquely flexible sensor, that can literally take measurements bent around corners or woven into fabrics.

It consists of a flexible cylindrical tube with spade electrical connections at either end. The Stretch Sensor behaves like a variable resistor, the more you stretch it the higher the resistance. Release the elastic and the resistance returns to normal.

How does it work?

As the length of the Stretch Sensor alters so does its resistance. For each centimetre of length change there is a a change in resistance of about 400ohms


You can view price information or order stretch sensors online via the sales page. Calculate the desired length for your application based based upon an extension of 100%. For example a 10cm sensor would extend 10cm to give a total length of 20cm.

All Stretch Sensors have a core diameter of 2mm. The diameter at the electrical
terminations is about 6mm

Note: lengths are the active stretch area and do not include the electrical terminations.

Simple Bridge Circuit
The following circuit demonstrates a simple bridge circuit configuration.

This is not a high precision configuration as the base resistors on the bridge have been selected to give a reasonable span of 3v without further amplification (normally these resistors should be proportionally high compared to the resistance value that is changing).
The opamp (LM662) is configured as a voltage following and has rail-to-rail inputs and outputs.
The purpose is to make the output compatible with a->d inputs (select high GBP). The bridge should be balanced using a potentiometer (22k) to give a maximum deflection when the sensor is relaxed, which should drop to near zero when extended to 100% of the resting length.

This circuit is convenient because you do not need to worry about virtual earths or bipolar supplies that a precision configuration would need to account for.
The poteniometer should be selected to have a similar range to the stretch sensor being measured.

- 2 x 20cm Stretch Sensors
- 2 x 10cm Stretch Sensors
- Data Aquisition Board
- CD with application notes
- PC Based display application (Windows XP, Windows NT, Windows 2000)

The PC software also includes a sample "breath detection mode" which enables respiration rate to be detected when a sensor is positioned around a person's chest.