Biometric signals with Arduino: heart rate and Galvanic Skin Response

While keeping on brainstorming ideas of how to the installation, the first technical test is to find a way to understand the emotions of people, possibly on device that they can wear pretty easily (like gloves or bracelet or head band).

So we thought: why not making a wearable version of a truth machine (aka the lie detector) that we see so often in US police tv series? Technically speaking they are not super sophisticated machines: they measure the heartbeat rate, the level of arousal (basically how much a person is stressed or excited) by measuring the galvanic skin response (from now on GSR) and the more advanced also the ECG and the breath frequency.

We have decided to go for the easy one, so we’ll just measure the HR and GSR… and for the moment we won’t care too much about the wearability of the device.

Heartbeat rate

Many Arduino based projects already record the HR, but mostly all of them just interface the arduino with a sport heartbeat belt. But if you go to visit an art exhibition you don’t want to undress yourself to wear the belt, so we kept searching for something else, small and easier to wear. And we found it!

On Kickstarter there is a cool project called Pulse Sensor, which is HR sensor that measure the transparency of the skin and how that change when the blood flows. They have already reached the funding needed: I ordered 2 of them and they will arrive hopefully soon. So when they arrive I’ll start making some tests with them.

Galvanic Skin Response

This one is pretty easy to build: it’s based on the idea that when you are stressed, or anxious or excited, you start micro-sweating, and that humidity increase the conductivity of your skin: so by measuring how resistance change, you can understand when people get excited or stressed. There was an article about biosensing on Make Magazine.
I also found a nice blog post with some code.

Beneath here is a picture of a prototype that uses 2 tiny copper foils as probes attached to fingers.

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