Simple and Inexpensive Heartbeat Detector

There are many ways to detect a heartbeat electronically. One of the simpler ways is to take [Orlando’s] approach. He’s built a finger-mounted pulse detector using a few simple components and an Arduino.

This circuit uses a method known as photoplethysmography. As blood is pumped through your body, the volume of blood in your extremities increases and decreases with each heartbeat. This method uses a light source and a detector to determine changes in the amount of blood in your extremities. In this case, [Orlando] is using the finger.

[Orlando] built a finger cuff containing an infrared LED and a photodiode. These components reside on opposite sides of the finger. The IR LED shines light through the finger while the photodiode detects it on the other side. The photodiode detects changes in the amount of light as blood pumps in and out of the finger.

The sensor is hooked up to an op amp circuit in order to convert the varying current into a varying voltage. The signal is then filtered and amplified. An Arduino detects the voltage changes and transmits the information to a computer via serial. [Orlando] has written both a LabVIEW program as well as a Processing program to plot the data as a waveform. If you’d rather ditch the PC altogether, you might want to check out this standalone heartbeat sensor instead.

Medical Tricorder Mark I

A handheld tricorder is as good a reason as any to start a project. The science-fiction-derived form factor provides an opportunity to work on a lot of different areas of hardware development like portable power, charging, communications between sensor and microcontroller. And of course you need a user interface so that the values being returned will have some meaning for the user.

[Marcus B] has done a great job with all of this in his first version of a medical tricorder. The current design hosts two sensors, one measures skin temperature using infrared, the other is a pulse sensor.

For us it’s not the number of sensors that makes something a “tricorder” but the ability of the device to use those sensors to make a diagnosis (or to give the user enough hints to come to their own conclusion). [Marcus] shares similar views and with that in mind has designed in a real-time clock and an SD card slot. These can be used to log sensor data over time which may then be able to suggest ailments based on a known set of common diagnosis parameters.

Looking at the image above you may be wondering which chip is the microcontroller. This build is actually a shield for an Arduino hiding underneath.

There’s a demonstration video after the break. And if you find this impressive you won’t want to miss the Open Source Science Tricorder which is one of the finalists for the 2014 Hackaday Prize.

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Immersion: Video Game Biofeedback


We’re not sure how scientific the following hack is, but it’s certainly interesting. Designer [Samuel Matson], interested in the correlation between gaming and stress, has pieced together a device that provides biofeedback during gameplay. He referenced this /r/gaming thread—which measured a player’s heart rate during a Halo session—as well as conducted his own tests that monitored the heart rate of gamers. After several iterations, [Samuel] had the above-pictured headset, which features the familiar and hackable pulse sensor placed by the earpiece.

The headset uses a TinyDuino and a Bluetooth TinyShield to communicate to the gamer’s computer in real time. He didn’t stop with simply monitoring heart rates, however; he integrated the signal into the game design. [Samuel] used indie-favorite game engine Unity3d to create a third-person shooter that reacts to the pulse sensor by raising the difficulty level when the player’s heart rate increases. It seems that his goal is to reduce or control stress among players, but we suspect inverting the model may be more effective: have the game cut you some slack when you’re stressed and present a challenge when you’re mellow.

[Thanks Ken]

Heart-shaped heart simulator


A few years ago, [Addie] over at Tymkrs put together a spooky little Halloween project: a small Propeller board that emulates the electrical signals in a heart. As a cardiac nurse, she thought her project could use a little improvement, and after two years she’s finally done. It’s a heart-shaped board that simulates electrical signals moving through the heart.

There are several key areas that conduct electrical signals through the heart – the sinoatrial node, atrioventricular node, and bundle branches all work like players in an orchestra to keep a heart beating like it should. If something goes wrong with one of these, the heart goes into tachycardia or fibrillation – not good, by any measure. [Addie]’s board simulates all the different ways a heart can go wrong with LEDs standing in for the electrical signals in a real heart. The name of the game here is to look at the LEDs and tell what state the heart is in.

The PCB heart is just one part of [Addie]’s heart simulator. The simulated heart can also plug into a neat little heart-shaped project box wired up with a solenoid, LCD display, headphone jack, and other electronics to turn this electronic heart into a complete study tool for heart rhythms. The nurses in [Addie]’s unit love the thing, and it looks like [Addie] might have a real cardiac training tool on here hands here.

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Pulse oximeter displays blood oxygen levels on a PC

The last time you were in the emergency room after a horrible accident involving a PVC pressure vessel, a nurse probably clipped a device called a pulse oximeter onto one of your remaining fingers. These small electronic devices detect both your pulse and blood oxygen level with a pair of LEDs and a photosensor. [Anders] sent in a great tutorial for building your own pulse oximeter using a fancy ARM dev board, but the theory behind the operation of this device can be transferred to just about any microcontroller platform.

The theory behind a pulse oximeter relies on the fact that hemoglobin absorbs red and infrared light differently based on its oxygenation levels. By shining a red and IR LED through a finger onto a photoresistor, it’s possible to determine a person’s blood oxygen level with just a tiny bit of math.

Of course a little bit of hardware needs to be thrown into the project; for this, [Anders] used an EMF32 Gecko starter kit, a great looking ARM dev board. After connecting the LEDs to a few transistors and opamps, [Anders] connected his sensor circuit to the ADC on the Gecko board. From here it was very easy to calculate his blood oxygen level and even display his pulse rate to a PC application.

Yes, for just the price of a dev board and a few LEDs, it’s possible to build your own medical device at a price far below what a commercial pulseox meter would cost. FDA approval not included.

Measuring a pulse with infrared light

The next time you’re unfortunate enough to make your way to a hospital, emergency room, or urgent care clinic, you’ll be asked to attach a small pulse monitor to your finger. The device the nurses clip on to one of your remaining digits is called a photoplethysmographic sensor, and basically it is able to read your pulse through reflected light. In the search to find out how these devices actually work, [Raj] sent in a great tutorial covering the theory behind photoplethysmographicy, and also built a simple device to detect a pulse without using a microcontroller.

These photoplethysmographic sensors operate by shining light into someone’s flesh – usually a finger or ear lobe – and recording the light reflected back to the source. The volume of blood in the finger will have an effect on the amount of light reflected back, and makes for a perfect way to automatically measure someone’s heart rate.

To build his device, [Raj] used a TCRT1000 reflective optical sensor. Inside this sensor is an infrared LED and a phototransistor. Of course with a finger over the sensor there is a ton of noise both from ambient light and the base rate of reflected light from a piece of flesh. [Raj] filtered this out, leaving only the small variations in the amount of reflected light, thus creating a very simple – and very inexpensive – electronic pulse meter.

Monitor your heartbeat with a webcam and a flashlight

After seeing some heart rate monitor apps for Android which use the camera and flashlight features of the phones, [Tyson] took on the challenge of coding this for himself. But he’s not using a smart phone, instead he grabbed a headlamp and webcam for his heat rate monitor.

To start out he recorded a test video with his smart phone to see what it looks like to cover both the flash LED and camera module with his thumb. The picture is mainly pink, but there’s quite obviously a color gradient that pulses with each gush of blood through his skin. The next task was to write some filtering software that could make use of this type of image coming from a webcam. He used C# to write a GUI which shows the live feed, as well as a scrolling graph of the processed data. He took several tries at it, we’ve embedded one of the earlier efforts after the break.

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