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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.

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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. 

WHAT'S UP?

CURRENT PROJECTS:

If you would like me to put more effort into one of these projects, please send an email telling me which one.

 

The WheeStat Potentiostat.

After years of slow development, we finally have our new model in stock.  The Pico 2.1 boasts a number of design improvements and can source +/- 40 mA. We are working on a high current module that will increase the current output.

 

Spectroscopy Projects.

The spectrometer is coming along.  This is a project that deserves more attention than I have been giving it.  We recently found out that integration periods are limited by the software to about 56 ms or less.  The issue has to do with rolling over a 16 bit counter.  While the 56 ms limitation should not affect most applications, there are others (perhaps astronomical applications) may require longer integration times.  We are working on this and I think I have it fixed in new firmware.  If this is something you are concerned about, contact me at my gmail address and I will get back to you.

I began work on a microtiter plate reader based on our spectrometer. I am looking forward to getting back to that project.

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Electrocardiograph (ECG, also called EKG).

This seems like something that might be worthwhile.  While I have no plan to go through the paperwork to get FDA approval, there are a lot of people in the world who I think would benefit from the availability of low cost medical devices, especially in lower income countries.  I have already submitted a circuit board for fabrication.  Here is a link to the design we are starting with.  A schematic is presented on page 19.

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Stuff we have done recently:

Electrochemical Detector for Capillary Electrophoresis:

  Work during summer 2020 focused on developing an isolated, battery powered potentiostat for use in capillary electrophoresis.  The instrument is based on the Raspberry Pi Zero 2W communicating over WiFi with a windows based host computer.  The Pi and attendant electronics are powered using a 12 volt lead-acid battery. I think this went rather well, but I have not heard back from our partners on this project.

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Migration from Texas Instruments based microcontrollers:

I have decided that TI is just not interested in helping the Maker community.  While I feel like I could probably get them to work with me, They do not seem to play well with the community that I choose to serve.

While I have migrated our spectroscopy effort to incorporate the Arduino compatible Teensy 4.1, I am still looking at other Arduino compatible options.  Mostly, I plan to use the Raspberry Pi Pico. I plan to have our instruments contain an Arduino compatible bootloader so others in the community can modify and upload the code

 

 

 

CONTACT

4989 Tilley Creek Road

Cullowhee, NC 28723

Tel: 828-201-0233
 

 

Mail:  j6summers@gmail.com

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