Biosensors: breath, GSR, ECG

spektrolytespektrolyte
edited December 2015 in Electrodes
Not necessarily electrodes, but I would like to be able to measure skin conductance (GSR, Heart rate (ECG) and Breath rate.

ECG:  can I just stick an electrode on my chest?

Breath rate: I have used a device which is just two wires going to a small black dome (probably a thermistor), when tape near the nose it registers the changes in temperature that correspond to airflow in and out of the nostrils. So can I just wire in a thermistor to one of the inputs?

GSR: Don't know how to achieve this.

Comments

  • wjcroftwjcroft Mount Shasta, CA
    The Search box at lower right of the page will turn up the previous GSR thread,


    ECG is covered in the OpenBCI tutorial docs,


    Not sure what is in your dome. Have you tried connecting it to a DVM to measure resistance, voltage, etc.? If you rig up a circuit that provides a proportional voltage, say from 0 to .1v (100 millivolts), you could route that to one of your channels. Also see the tutorial for how to adjust the scale factor used on each channel.

    Seems to be a lot out there on the web,


    William
  • spektrolytespektrolyte
    The dome has a resistance of around 8.5k at my room temperature. Warm breath raises this slightly, cold breath lowers it so am pretty sure it is the same as connecting a potentiometer to the arduino.

    Tracing voltage fluctuation over time would give a good representation of breathing oscillation providing your room temperature is not the same as your warm breath temperature. I am not sure why all of the breath sensor options found online are so complicated in comparison.

    Also found this very simple GSR guide using two finger straps: http://ftmedia.eu/diy-gsr-sensor/

    If it's possible to measure GSR & breath rate using the two non-EEG inputs on the OpenBCI it leaves plenty of free channels for heart monitoring and neurofeedback.

    Interestingly I can find nothing online about making a pIR HEG sensor. It is essentially a co2 sensor which is calibrated for tracking minute changes in temperature fed into an opamp and the output then sampled. Other than that I am not sure about how to implement it and there is no reason why they should cost more than about $10 to produce. Couple it with a Raspberry PiZero and a boot loaded script which displays a warp-tunnel movie controlled by blood flow and you have a $25 device which plugs into any TV and cures ADHD in a couple of months.



  • biomurphbiomurph Brooklyn, NY
    An easy way to include some simple analog signals into your data stream is to attach the sensors to the analog pins of the on-board 32bit board. I have put up a working code example on our github here.
    This example connects the analog sensor to OpenBCI pin D13, which is also A7. If you build a resistor divider with your dome sensor, you can connect it's output to A7. This code will put the ADC value (10 bit result, 0 to 1023) into the auxData array. The auxData array is an array of 3 short variables (shorts are 16bit values). 
    You can modify this code to attach another sensor, like your GSR sensor, and include the result in one of the other auxData array positions.
    This code will take analog readings at the ADS sample rate.

    Check this doc for notes on which pins are analog inputs, and what they are called:

    I recommend using D12 (A6) for your purposes.
  • spektrolytespektrolyte
    edited December 2015
    Awesome, thanks.



    PulseSensor looks perfect for measuring heart rate, and the GSR sensor is detailed above.


    It requires 2 analog pins and SMBus / I2C. Can this be used with the 32-bit board?

  • biomurphbiomurph Brooklyn, NY
    Pulse Sensor is great for measuring heart rate.
    Unfortunately, we don't have access to the hardware I2C. It's possible to bit-bang I2C, but we have not implemented it yet. Software I2C is on our radar.
  • spektrolytespektrolyte
    How about a second arduino (nano) reading the I2c from the thermometer, which sends the rate of change via a digital output into D18?


  • spektrolytespektrolyte
    That won't work. Digital inputs are on/off, but it could use an analog input,

    GSR, Pulse & Breath on the 3 analog pins, and the HEG sensor sampled by one of the 8 EEG channels.


  • biomurphbiomurph Brooklyn, NY
    I'm not sure about your plan. Looks like the HEG sensor is I2C, which we don't have implemented in software yet.
    What are the metrics you are collecting? It is possible to use one of the OpenBCI channels to measure heart rate (ECG) if that helps.
Sign In or Register to comment.

© Vanilla Keystone Theme 2026