A Fitness Watch Which Can Monitor Bacterial Growth

Bacteria play an important role in our lives. They could be beneficial and give us medicines, beer, food ingredients etc. Continuously monitoring the growth phase and the concentration of bacterial cells is a crucial process. This is an important routine in both industrial and academic labs. Optical density(OD) is one of the most widely used forms of representing bacterial concentration and track their growth.

Currently, continuous monitoring of bacteria growth remains unaddressed. Using the existing methods, a scientist would have to periodically check the OD of the bacterial solutions quite often. Despite being labour intensive and time-consuming, it also poses the risk of contamination and waste of plastic consumables.

To solve this, we have now made a novel continuous OD meter by hacking a low-cost generic fitness tracker, the details of the construction are outlined below
The results are published in the research journal and can be found with the link below, https://pubs.acs.org/doi/abs/10.1021/acs.analchem.9b02628

> Voltage Regulator

1

$1.20

TPS709B33DBVT

https://ie.farnell.com/

> Current Regulator

1

$0.42

NSI45020AT1G

https://ie.farnell.com/

> LED

1

$0.15

C503B-AAN-CY0B0251

https://ie.farnell.com/

> ID107 HR fitness tracker

1

$12.30

ID107

http://www.idoosmart.com/c2416.html

Tools used

Windows PC, 3D printer, Hot glue gun, Soldering station, and Black Magic Probe.

Note: These are tools used and are considered as one-off costs only.

Firmware instructions for ODX

Note that these instructions are taken from the GitHub repository (https://github.com/sandeepmistry/arduino-nRF5) of sandeepmistry who originally provided the Arduino core for the nRF devices as stated in the ODX manuscript. Here, we provide the instructions of the firmware specifically adopted for the ODX device that contains nrf51 device using Windows PC.

4.1. Board Manager

a) Download and install the Arduino IDE (At least v1.6.12)

b) Start the Arduino IDE

c) Go into Preferences

d) Add https://sandeepmistry.github.io/arduino-nRF5/package_nRF5_boards_index.json as an "Additional Board Manager URL"

e) Add https://micooke.github.io/package_nRF5_smartwatches_index.jsonas an "Additional Board Manager URL"

f) Open the Boards Manager from the Tools -> Board menu and install "Nordic Semiconductor nRF5 Boards"

g) Select ID107 HR from the Tools -> Board menu

4.2. Flashing a Soft Device

a) cd , where is your Arduino Sketch folder (Windows: ~/Documents/Arduino)

b) Create the following directories: tools/nRF5FlashSoftDevice/tool/

c) DownloadbnRF5FlashSoftDevice.jar to /tools/nRF5FlashSoftDevice/tool/

d) Restart the Arduino IDE

e) Select your ID107HR from the Tools -> Board menu

f) Select a SoftDevice S130 from the Tools -> "SoftDevice: " menu

g) Select a Programmer (BMP) from the Tools -> "Programmer: " menu

h) Select Tools -> nRF5 Flash SoftDevice

i) Read license agreement

j) Click "Accept" to accept license and continue, or "Decline" to decline and abort

k) If accepted, SoftDevice binary will be flashed to the board

4.3. Flashing a ODX firmware

a) Download all the files from the from the firmware folder in the github link https://github.com/momos123/ODX/tree/master/firmware

b) Open the ODX.ino with Arduino IDE

c) Select your ID107HR from the Tools -> Board menu

d) Select a SoftDevice S130 from the Tools -> "SoftDevice: " menu

e) Select a Programmer (BMP) from the Tools -> "Programmer: " menu

f) Select the BMP port as the Port on Arduino IDE

g) Upload the ODX.ino