Contact tracing with a Raspberry Pi Zero-W

Contact tracing via smartphone apps has been widely touted as an important way to control and limit the spread of the COVID-19 epidemic. However, basing contact-tracing on phone apps has several limitations. Here are instructions for constructing a contact tracing device prototype with a Raspberry Pi Zero-W . The constructed device is compatible with the Apple/Google Bluetooth contact tracing specification. It runs the Epidose software, which is based on the DP3T "unlinkable" design.

Materials

Required materials

Assemble the following materials:

• Raspberry Pi Zero-W
• Micro SSD card (Minimum recommended size 8 GB)
• Small (3mm) red LED
• 330 Ohm, 0.25 W resistor
• Single SPST momentary push button; users press this to authorize the upload of their contacts to the Health Authority.

Circuit diagram

The objective of this construction is to provide the Raspberry Pi with a switch to authorize the contact upload and a LED to indicate that a user is at risk. The circuit diagram above shows this setup.

Connect the resistor to the LED

Resistor LED connection

Solder one end of the resistor (it doesn't matter which) to the LED's cathode (the shorter of the LED's two wires) to obtain a 17mm long connection. The connected assembly should be able to fit in pins 20 and 40 of the Raspberry Pi.

Isolate the LED-resistor connection

Isolating the connection

Cut 17mm of the smallest heat-shrink tube that can fit around the resistor and slide it to cover the entire LED-resistor connection. Heat it to shrink.

Solder components on the Raspberry Pi

Assembled Raspberry Pi

• Solder the free end of the LED to pin 40.
• Solder the free end of the resistor to pin 20.
• Solder the push button between pins 14 and 10 (orientation isn't important).

Power up and install the Epidose software

• Connect the Raspberry Pi to a power source. A power bank can make this setup portable.
• Follow the instructions in the Epidose repository repository to install and configure the software.
• You can test the hardware's operation by running the command sudo venv/bin/python epidose/device/device_io.py -t . This allows you to toggle the LED by pressing the button. Press Control-C and press the button to terminate the program.