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Introduction

The WheeCardio is a low cost electrocardiograph (ECG, also called EKG)  I plan to have two designs, one for indoor use with my bicycle trainer and the other for going mobile.  The two designs are described below.

User Interface

The figure above shows part of a screenshot of an ECG scan recorded with our hardware and user interface. The expected features in the ECG are apparent and the scan looks good. 

When working with the stationary use model, the user interface is capable of recording eight second scans (which can be saved on the host computer), or observing continuously in real time.  Saved data can be loaded from the host computer, or from any memory device (such as the SD card in the mobile model).

The display can show either 4 seconds of data (as shown above) or one beat, (0.65 seconds).  Each beat in an 8 second recording can be displayed and compared to the average beat.

Hardware for stationary use

The WheeCardio was designed to monitor heart function while exercising on a stationary bicycle.  It is composed of an amplification circuit and a Raspberry Pi Pico microcontroller development board.  

The stationary use board is powered over a micro-USB cable and transfers data directly to the host computer. 

The instrument requires standard ECG electrodes that can be purchased from a source like Amazon. We are using 3M Red Dot monitoring electrodes and have found them useful.  The current model uses alligator clips to connect to the electrodes.  We have ordered snap on connectors and will evaluate them when they arrive.

The amp circuit is a modified version of a schematic found in the data sheet of the AD8236 instrument amp. It incorporates a low pass filter and a notch filter for removing high frequency and 60 Hz noise.

As shown in the figure at the right, the instrument fits in a compact 3D-printed box. 

WheeCardio_1.jpg
WheeCardio_2.jpg

Hardware for mobile use

The plan is for the user to press a button on the hardware to record eight second scans.  The data will be recorded on a micro-SD card and can be evaluated using the user interface when the user gets home. 

The mobile model is in the prototyping stage.  At the time I wrote this, we had designed and ordered a printed circuit board for the new mobile hardware but it had not arrived yet.

The mobile hardware will differ from the stationary hardware in these regards:

microSD_Adapter.jpg
  • It will be powered by a rechargeable battery and will store data on a micro-SD card.

  • It will have an input button to signal the instrument to begin recording.

  • It will have an RGB led to display function. 

At this time, we are prototyping firmware for the SD card using a micro-SD to standard-SD adapter with wires soldered to the microcontroller board (figure on above right)

Firmware

Firmware for the WheeCardio is written using the Arduino development environment for the Raspberry Pi Pico.  The stationary and mobile versions will likely have separate versions of the firmware.

Availability

Right now we are alpha-testing the stationary use model and are still prototyping the mobile model.  If you are interested in building one of these, or would like to purchase one, contact me at j6summers@gmail.com

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