Bloodlight: Improving Open-Source Blood Analysis

mobile phone with telemedicine video and a virtual hologram overlay running the Bloodlight app

The intersection between recent wave of wearables and the Covid19 pandemic has led to a surge of interest in the medical and diagnostic uses of fitness trackers and cheap medical sensors such as pulse-oximeters. With this wave has come a strong desire to make more useful diagnoses via additional measurable metrics such as breathing rate, blood oxygen levels, blood glucose levels and more. This is how we are improving open-source blood analysis.

Codethink is sponsoring open-source projects to further the state-of-the-art and showcase our technical capabilities in software and electronics. The idea to develop a medical research device came from our engineers.

What is Bloodlight?

Bloodlight is a freely available open-source prototype design for a medical PPG research device. Researchers can use Bloodlight devices to analyse components in the blood by comparing the intensity of the reflected light of different colors. This technique is known as spectroscopy and is remarkably similar to how we determine stars’ chemical makeup.

As an open-source project, all the source code and hardware designs are available freely. The parts used in the design are all inexpensive. Therefore, the devices can be made for less than $50 per unit even for small runs of 10 devices.

Capturing medical data with light

Photoplethysmography (PPG) is a non-invasive technique for measuring the properties of blood using light, and a way for improving open-source blood analysis.

Pulse oximetry is a class of PPG that detects the oxygen saturation of the blood. It is used in hospitals to detect the vital signs of patients. Another application is pulse monitoring functionality commonly seen in smartwatches.

The PPG’s light measures the blood’s properties by shining light into the body, and the light that comes back out is recorded. For pulse oximeters work in transmissive mode; the light travels straight through a finger and is detected on the other side. On the other hand, smartwatches operate in reflective mode; the light enters the wrist and is reflected back into the sensor on the wrist’s same side.

Bloodlight can support research in both reflective and transmissive modes.

While fitness trackers and pulse oximeters utilise only 2-3 wavelengths (frequencies) of light and sample at up to a few kilohertz, Bloodlight can simultaneously measure up to 16 wavelengths at frequencies up to 4MHz. With Bloodlight, we can measure changes in the audio frequency range, and we hope that with correct calibration, this may enable us to read audio signals directly from the bloodstream.

What is in our blood?

Haemoglobin is a protein found in red blood cells. It carries oxygen from the lungs out to where it is used in muscles and organs. As the oxygen is used, it is turned into carbon dioxide, and then transported back to the lungs to exhale.

Oxygenated Haemoglobin (HbO2) and deoxygenated Haemoglobin (Hb) absorb different wavelengths of light to various degrees. Pulse oximeters use two wavelengths of light; red and infrared. These are chosen because they allow the difference between Hb and HbO2 to be characterised.

Devices like Bloodlight can be used to investigate additional components of blood, as well as Hb and HbO2.

Why Open-Source Blood Analysis?

At Codethink, we believe it is essential that we work in the open and document our practices to sustain a medical improvement in the future. Our open-source approach will allow us to collaborate with Universities and device-manufacturers, to provide a base upon which they can perform further blood analysis research.

We hope that our work can form the basis of improvements in the accuracy and scope of measurements taken by a fitness tracker. We are aiming at improving open-source blood analysis.


With the right collaboration, we believe it’s possible to use sensitive PPG techniques to detect:

  • Glycated Haemoglobin to see indicators of diabetes
  • Lactic Acid levels to assist in optimising exercise regimes
  • Blood carbon-dioxide and monoxide to detect respiratory or air quality issues

How can I help?

We can currently collect many data, but our data processing isn’t yet mature enough to analyse what most of it means. We can see clear pulse-signals at multiple wavelengths, and fundamental frequency analysis has shown us some additional signals.

If you have a background in blood research or are currently designing a wearable/medical PPG device, we’d love to get in touch and have a chat, to see where we could collaborate or assist in improving open-source blood analysis.

For more in-depth technical information, please read:

Article written by Ben Brewer & Michael Drake


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