Electronics Team #5 Week February 30-March 5

At current we have independent prototypes for Button Input and Bluetooth communication.

Button Input Prototype

To start with we have the input prototype. This is to show that the general circuit for the armband (criss-crossing conductive fabric seperated by a perforated insulator) can be implemented, and to get familiar with the Teensy development process.

In this prototype, the button pad is polled several hundred/thousand times per second. The way this works is each pin connected to a row on the pad is set as a high impedance input with an activated pull up resistor. One column is then set as a low / GND output, with all other columns set to high impedance by making them inputs. If a contact is closed between a row and a high impedance column, no current flows, and the entire assembly is held at Vcc, and is read as a '1' by the Teensy. If a contact is closed between a row and the GND column, current flows to GND, and the assembly is held at GND, meaning it is read as a '0'.

To ensure we got this right, our 4 buttons are tied to individual LED's on an LED array, and they'll light up when the corresponding contact is detected as closed.

Bluetooth Communication Prototype

For this prototype we wanted to demonstrate Bluetooth communication between an electronic device and the Android phone. This circuit is for another class, where in an accelerometer is being used to track a robot's orientation relative to gravity. 

In this circuit, an Atmel ATTiny85 (far left) reads analog values coming off the accelerometer (lower middle), and sends those values via serial to the Bluetooth module (upper middle / red PCB w/ LED). The Bluesmirf acts as a serial bridge, packetizing the serial data it receives and transmitting via Bluetooth. This data is then read by the Android phone as coming over a BluetoothSocket, and is used to update the display.

Summary

We have two prototypes that demonstrate the most technically challenging parts of our project. Over the course of this week the two will be combined into a single prototype, and fed into the main android app.

Additionally, we've now received the parts for different components of the device- once the integrated prototype is working, the next steps are the RFID based security, and building a simple digital compass from a magnetometer and accelerometer.