Fitness Tracker Hacked Into Optical Density Meter

What do fitness trackers have to do with bacterial cultures in the lab? Absolutely nothing, unless and until someone turns a fitness band into a general-purpose optical densitometer for the lab.

This is one of those stories that shows that you never know from where inspiration is going to come. [Chinna Devarapu] learned that as a result of playing around with cheap fitness bands, specifically an ID107HR. A community has built up around hacking these bands; we featured a similar band that was turned into an EEG. With some help, [Chinna] was able to reflash the microcontroller and program it in the Arduino IDE, and began looking for a mission for the sensor-laden platform.

He settled on building a continuous optical densitometer for his biology colleagues. Bacterial cultures become increasingly turbid as the grow, and measuring the optical density (OD) of a culture is a common way to monitor its growth phase. This is usually done by sucking up a bit of the culture to measure, but [Chinna] and his team were able to use the hacked fitness band’s heartrate sensor to measure the OD on the fly. The tracker fits in a 3D-printed holder where an LED can shine through the growing culture; the sensor’s photodiode measures the amount of light getting through and the raw data is available via the tracker’s Bluetooth. The whole thing can be built for less than $20, and the plans have been completely open-sourced.

We really like the idea of turning these fitness bands into something completely different. With the capabilities these things pack into such a cheap and compact package, they should start turning up in more and more projects.

5 thoughts on “Fitness Tracker Hacked Into Optical Density Meter

  1. It’s worth noting that optical density is somewhat wavelength dependent with 600nm / yellow light being the common choice. Certain species give more consistent results under different wavelengths. Since heart rate monitors are generally optimised for detecting red and near IR light, I wonder how this compares to a more purpose built spectrophotometer.

    1. Seems like they did address this. From the linked article: “One important modification we did to the fitness is adding a circuit to drive an LED at 600nm. This is important because ODs are traditionally measured at 600nm, where most bacteria has low absorption of light.”

  2. I appreciate seeing a project that is relevant to both the DIY community and the scientific-research community! IMO each group could learn lots from the other; projects like this one demonstrate that. Great work!

Leave a Reply to DannyCancel reply

Please be kind and respectful to help make the comments section excellent. (Comment Policy)

This site uses Akismet to reduce spam. Learn how your comment data is processed.