Chin controlled sewing machine
John has a spinal chord injury at chest level and uses a manual wheelchair.
He is an engineer and very much likes to work problems through himself. John bought an electric sewing machine so that he can sew bespoke articles for himself. However, he is unable to use his elbow to push the foot pedal because of his injury, and he needs his arms to steady himself to feed the material through the machine. To overcome this obstacle he rigged up something that goes round his neck to work the foot pedal and that works fine, but he feels that it would be great if the foot pedal was wireless or controlled via Bluetooth.
The solution
An Adafruit Feather nRF52 Bluefruit LE module was chosen by Bob White, Remap volunteer, as the core component to implement a Bluetooth Low Energy link between the pedal and the sewing machine. This is an Arduino-compatible module combining a powerful microcontroller with a Bluetooth low energy interface that can be operated as a peripheral and a client.
The Bluefruit LE module has an integrated charging system for a Lithium-polymer battery; a 250mAh battery giving in excess of 24 hours of operation.
A Sender unit was integrated with its battery inside a modified sewing machine pedal. The signal from the pedal’s variable resistor is read by the Bluefruit LE module to create a 7-bit demand. This digitized demand is communicated to a Receiver unit ten times per second. On receipt of a valid demand command the receiver converts this back to an analogue signal to emulate the presence of a passive foot pedal connected to the sewing machine.
The system employs safety features such as detection of low battery levels and the loss of communication to immediately shut down the demand sent to the sewing machine. The Sender and Receiver feature a status LED to indicate to the user normal and fault conditions.
Adafruit provide a free IOS and Android app that can be used to communicate with the Receiver unit to display an estimate of remaining battery capacities for the Sender and Receiver. If capacity is low, the user can charge the Sender and Receiver via the integrated micro-USB connector compatible with many mobile phone chargers.
Photos show the pedal with Bluetooth sender assembly, and the sewing machine receiver unit, and the sewing machine in operation
The benefit
The device is now fully operational and was provided with relevant safety information appropriate to low energy Bluetooth components in proximity of medical devices. John is very happy with the improved independence and diversity that this new controller now provides to his sewing skills. The video below shows John using the new device.
The architecture and components of this solution lend themselves to a wide range of applications where limited mobility may prohibit the use of standard control devices. The Sender unit developed for this sewing machine application features multiple analogue and digital inputs making it capable of interfacing to a range of user-input devices such as joysticks. The Bluetooth low energy link created is robust and fault tolerant thus making it suitable for commanding potentially hazardous motorized devices. The lack of wireless interfaces such as Bluetooth on many items used in our daily lives can be overcome by emulating the legacy interfaces used on these devices.
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