The Curl muscle sensor galvanically captures electrical signals produced by muscles near the surface of the skin. These signals are roughly proportional to the amount of tension being generated by the muscle. The sensor is designed to record the activity of medium and large muscles, although the smaller the muscle the larger will be the signal.

Safety first !

To use the sensor without being tethered to your computer or MIDI device and ensure electrically safe operation, use the Curl with the Wi-microSystem and one of our BatteryPacks.

How to use the Curl

To ensure reliable operation, the electrode must be secured to the skin, preferably with double-sided tape. We recommend 3M medical grade tape, which is non-allergenic. 3M double-sided tape #1522 comes in 1 inch x 72 yard rolls, which can be cut to size -- it can be obtained from medical supply companies. Holes should be punched in the tape so that the round metal contacts are in direct contact with the skin. Secure contact between the metal contacts and the skin is vital for proper functioning of the sensor.

The beige patch electrode is a standard electrode that can be purchased from medical supply companies. These electrodes are normally used for electrical stimulation of skin or muscle. In the case of the Curl muscle sensor, it serves only as a passive reference ground for the sensor electronics. There is no current being passed through the electrode. To increase the life of the patch electrode, wet the surface and stick it to the plastic sheet after use. The patch electrode is needed to reduce electrical noise such as that generated by lights and appliances. It should be placed over a bony area such as the wrist, ankle or knee and stick securely to the skin.

The gain of the output signal can be adjusted by rotating the slot on the potentiometer, which is accessible through a small hole drilled in the top of the sensor. Turning the slot counterclockwise will increase the size of the signal. Exercise caution when changing the gain because the potentiometer can be easily damaged if too much force is exerted. The range of motion of the potentiometer is less than one turn and there are physical stops at either extreme. Exerting too much force will destroy the stops, making it difficult to judge the gain setting.

Which muscles to sense

Typical muscles which should give reliable signals include: muscles of the forearm related to flexion or extension of the wrist and extension of the fingers, muscles of the upper arm which flex and extend the elbow, shoulder muscles and muscles of the shank which flex and extend the ankle. The muscles of the thigh which flex and extend the knee are too large to give reliable signals unless they are very strongly activated. The amount of subcutaneous fat has a significant effect on the reliability and strength of the signal. The best signals will be obtained if the sensor is placed over muscles with the least amount of overlying subcutaneous fat.

Caring for your Curl

Clean the sensor using only water or mild detergent -- do not immerse, wipe with a soaked swab or cloth. Avoid getting liquids or particulate contaminants on top surface (particularly gain adjustment potentiometer)