This device tracks the angle of Julian’s calf. If his leg does not go perpendicular to the ground, for a given period of time, the device vibrates to remind him to put his heel flat. If the initial series of vibrations do not get Julian’s attention…the subsequent beeping always does!
The device consists of an accelerometer, vibrator motor, a piezo speaker, an LED and a switch; all managed by an ATTiny85 micro-controller. Housed in a 3d printed case. The main casing has a hole in its base through which passes a smaller case surrounding the vibrator. The vibrator and its casing are suspended by a spring from an arch inside the main housing and this protrudes out from the back of the main case. Suspending the vibrator like this allows it to be placed through the splint and it actually touches the leg—(i.e. sock). The vibrator casing is free from the main circuit housing which makes less rigid/fragile, and also allows for a greater vibration sense at the back of the calf.
How it works
The device is turned on while Julian is wearing his splints. It calibrates itself to the angle it is at when switched on, and uses this angle as its future reference angle to compare to.
To prevent the device from activating during walking, there is a 10 second 'grace period' before it vibrates. So, if the current angle is less than the initial ‘good’ angle for more than 10 seconds, it vibrators for a second. If the angle remains bad for another 5 seconds it vibrators longer. It gives four warning vibrations separated by slight pauses and finally, if the angle continues to remain bad, the device beeps.
With the outer, top casing removed, you can see in the lower left portion of the image, the vibrator casing protruding of the flat frame. Above that is the arch attached to the spring supporting the vibrator.
To prevent the vibrator from getting damaged by the splint and to allow for a more powerful vibration to the leg, the vibrator component had to separate from the main casing. On the left is the vibrator similar to those in most mobile phones. Basically, the motor is spinning an asymetrical weight at the end of the shaft. This part is placed into the case on the right. The spring is at the top and is the only thing attached to a supporting arch in the main housing of the device.
Vibrator & case
Most of the components are visible here. To save space, the accelerometer is inverted and attached to the underside of the circuit, directly below the chip. The three sets of wires leading off are power, LED and switch. This was a big mistake, as it was almost impossible to manipulate the top of the case while attached to the bottom!
Behind the yellow and black wire is the arch supporting the spring which holds the vibrator in its casing against the leg. Not only does the spring allow for a more powerful vibration, it also permits the vibrator casing to adjust its depth to always touch Julian's calf directly. So it doesn't matter what socks he wears for example.
Arch with vibrator
Conclusion and considerations
All in all, quite satisfied for a first prototype. Many areas of improvement possible however! It is too big. There is no power management. With a few extra components it could even serve as a rudimentary gait analysis.