What it shows
Each heartbeat changes the amount of blood in the fingertip, and so changes how much light passes through or reflects. A green LED and a light sensor see this tiny change, which the Arduino turns into a beat rate.
The science
Blood absorbs green light. When the heart pumps, the fingertip fills with blood and absorbs more light, so the sensor reading dips a little, then recovers: the signal swings by a few percent in time with the pulse. The sketch finds the peaks that cross a changing threshold, measures the time between two peaks in milliseconds and calculates beats per minute as 60000 divided by that interval.
Materials
Cost: under Rs 1,500. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- An Arduino Uno or compatible board
- A pulse sensor module (analog, 3 to 5 V)
- A red LED and a 220 Ω resistor
- A 16 x 2 I2C LCD or the Serial Plotter
- A breadboard and jumper wires
- A velcro strap or tape
Safety
For this project: USB power only. This is a school demonstration, not a medical device. Do not use it to decide anything about health.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Connect the sensor signal to A0, the power to 5 V and GND to GND.
Connect the red LED with its 220 Ω resistor to pin 13 and GND.
Upload a sketch that prints analogRead(A0) every 20 ms and open the Serial Plotter.
Rest a fingertip lightly on the sensor, keep still and note the waves that appear in the plot.
Find the average of the last 100 readings and use it as the baseline.
Detect a beat when the reading rises above the baseline by a set margin, and ignore anything within 300 ms of the last beat.
Calculate beats per minute from the time between beats, average the last four, and light the LED on each beat.
Compare it with counting your pulse at the wrist for 30 seconds, then repeat after a minute of jumping.
What you should see
The Serial Plotter shows a wave that matches your pulse, and the calculated rate is close to the wrist count and rises after exercise.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1How does light detect a pulse?
Blood absorbs light, so the transmitted light changes with each beat.
2How is beats per minute calculated?
60000 divided by the time between beats in milliseconds.
3Why ignore peaks within 300 ms?
No human heart beats faster than 200 times a minute, so such peaks are noise.
4What affects reading quality?
Finger movement, room light and pressure on the sensor.
Take it further
Record pulse every minute for ten minutes during rest and after exercise and plot the recovery curve.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Science projects
Investigatory Projects for Class 11 and 12
Topics, method and report structure for physics, chemistry and biology
Find out more about electronics and robotics
Free, well-known places to explore the subject further. Ask a grown-up before you sign up for anything or type your name anywhere.