ECG ADC Buffer Flex Module

ECG Sensor summing amplifier and RC filter for feeding Plessey biosensors to an ADC. For sale on Tindie.

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This is a buffer and filter for bio-sensors. It is specifically designed for the Plessey EPIC low-cost sensors.

This board is part of Fyber Labs Flex Module project.

Biopotential signals are low frequency small voltage output that need very clean power and low cross-talk routing.

Example signal types(source):

  • EEG:
    Surface 5 mV 200Hz
    Scalp 300uV 100Hz
  • EMG:
    On skin 10 uVpp-1mVpp, 10Hz-1kHz
  • EOG:
    Frontal skull 100uVpp-1mVPP 10Hz-1kHz
  • ECG:
    Chest 10 uVpp-10mVpp, 0.1-100Hz

The board utilizes a Sallen-Key 2nd order low pass filter that can be set for filtering fc at 100Hz(16KOhm arrays).

Summing amplifier configuration allows for -3.3V to +3.3V signal conversion to 0-3.3V for ADC. Right now there is no actual amplification of the Plessey sensor until testing can be done. Additional digital filtering will likely be required as well.

Any software related will be released under BSD or MIT license. SAAS or cloud based software will be AGPL.

Creative Commons License

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  • Separating notch filter design to new project

    Chris Hamilton07/28/2015 at 20:56 0 comments

    I will be putting up design information for the notch filter version in a new project - ExG Notch Flex Module. This design should have some application if implementing a digital notch filter or in use outdoors.

  • Switching Op Amps

    Chris Hamilton06/24/2015 at 21:54 0 comments

    After a seminar by ST, I will be reworking the opamp to be a TSZ124. Also, Plessey recommends the low pass roll off be around 200Hz and that I use the 10x gain not the 50x gain sensors. So not the PS25251, but the PS25253 nor the PS25451, but the PS25454. The advanced Notch filter design works great, so I'll be releasing an updated version of it and this board (which is good for differential ADC) with a new low pass filter. I'll be working on a 2 channel design that utilizes the TSZ124 in both a filter and gain configuration soon.

  • Notch filtering

    Chris Hamilton01/11/2015 at 01:50 0 comments

    I am working on an analog notch filter design to add. It will also utilize arrays of resistors as 1% and 5% resistor arrays are available. Selecting capacitors for size will be more complicated. The current schematic on github as "notch" uses arrays and an 0402 version of the Twin T notch filter is coming. I take feedback from the same op-amp and the Sallen Key is now 3rd order and much stronger. All this for only an additional capacitor per input over a non-active notch design added to the current ECG buffer design. I'll be working on the board layout to help improve my own testing of the ECG sensors.

  • Updated Pictures

    Chris Hamilton12/18/2014 at 02:48 0 comments

    I added new pictures showing the new castellations. We are still evaluating the design of this Flex Module as we are experimenting with various Plessey EPIC sensors.

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c.lamport wrote 05/04/2015 at 16:22 point

Are there any schematics for this board? I've been working with EEG and I'd love to design a headset so I could map my mental states while sleeping

  Are you sure? yes | no

Chris Hamilton wrote 05/04/2015 at 16:40 point doesn't have the best UI or style.  Please see the github link "Schematics, layouts, etc." on this page for schematics and also the last image in the gallery is the schematic.  For the notch filter version it is still under development, but available in github as the "notched" directory.

  Are you sure? yes | no

michcfr wrote 11/17/2014 at 15:10 point
Would it works with this kind of strap chest belt? (it is made for the Garmin/Wahoo/Polar heart rate devices). Thx


  Are you sure? yes | no

Chris Hamilton wrote 11/17/2014 at 19:54 point
Hi, that specific item is just a holding strap for a heart rate device :). But, the device it can hold is self contained and transmits heart rate over ANT or Bluetooth directly to a compatible receiver. The signal is much simpler (just the heart rate), but transmitted by its internal radio to phones, exercise equipment, etc..

The ECG ADC Buffer Flex Module is designed to buffer and filter raw signals generated from the Plessey EPIC Sensors - which can receive a wide range of bioelectric potentials (ECG, EEG, EMG, etc.). So the flex module is designed to receive up to 4 signals from these sensors and 'clean' them before sending on to a microcontroller all on the same circuit board (a good ECG trace takes multiple sensor signals).

Depending on the sensor configuration, stable body positioning, filtering (either additional analog or later DSP), and the tuning of the specific Plessey EPIC Sensor you would be able to perform a wide range of complex health monitoring ie. a full ECG trace not just the heart rate. Getting a good low noise signal out takes much more effort and is something I am still experimenting with.

  Are you sure? yes | no

michcfr wrote 11/18/2014 at 11:04 point
Hi Chris,

No, no. It is not only a holding strap :-)
The strap contains sensors/electrodes, the two snap buttons you see, apart holding a particular bluetooth/Ant device, acts as connectors to the electrodes embedded into the belt.
So, I wondering if these electrodes are compatible with Plessey EPIC sensors?
I think it would be a good idea if you can make it usable with the ECG AC module...


  Are you sure? yes | no

Chris Hamilton wrote 11/20/2014 at 10:23 point
Hi, the Plessey sensors are more than electrodes and include a purpose built amplifier circuit and work in a variety of placements and more applications for lower cost. They are high impedance with capacitive coupling. It should simplify working with bio-electric signals. This board's main purpose is only to convert a bipolar -+3.3V signal from up to 4 Plessey sensors to a 0 to +3.3V signal for ADC input. Hope that helps. We will be making some projects demonstrating use in the near future.

  Are you sure? yes | no

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