Requirements

The main requirements for the project are:

• Robust
• Easy To Use
• Easy To Administer
• Low Power
• Secure

Robust

The device needs to be robust. Due to my son's condition he can be incredibly rough, and sometimes violent when he has a meltdown. If he has a meltdown and lashes out, he needs to not only NOT hurt himself on the device but the device needs to be able to withstand the punishment.

Easy To Use

The PECS system is very simple. Images represent the needs of the user, and communication takes place by simple selection of an image. The device needs to include this incredibly simple interface.

Easy To Administer

From the perspective of us parents, we need to be easily able to add/remove/update the choices available on the device.

Low Power

Keeping the power usage down is a definite plus. Since most of the time the device will just be waiting for an image to be selected, properly implementing low-power modes in the hardware is a definite design goal.

Secure

Since the device will be responsible for controlling what my son watches, the device needs to be built securely so that it presents as little an attack surface as possible for hackers. The last thing we want is the list of shows/videos that can be shown to be replaced with content that is not suitable, or even illegal.

Initial Thoughts

My initial thoughts on the hardware for the device are a Raspberry Pi 3 connecting to my home network via WiFi. This way, I can leverage the security features of Linux, the ease of developing the software stack to control the device, and the hardware support for serial device protocols (I2C, SPI, etc).

For the front end interface, I am thinking 6 small 2.4" 320x240 TFT display modules connected to the Pi via SPI to display the PECS images. To perform the actual selection sensing, I am thinking of using Capacitive Touch Sensors made from a thin layer of clear acrylic, then a layer of Indium Tin Oxide coated plastic film, then a thick layer of clear acrylic behind it for strength, then the TFT mounted behind that.

To implement the low-power states, if the board hasn't been used for some time, the TFT displays can be powered down and the backlights turned off under software control. The capacitive touch sensors or even an accelerometer could sense the device being touched, and power the displays back on.