Medical89

It's been a while since I posted! In the last post I presented my DIY wireless ECG. Today, I want to follow up on that post. In the last two years I added more and more consumer medical devices and features to the ECG that one might call it a DIY patient monitor 😀

I recorded myself using it in this video. I deprived myself of oxygen and watched the result on the monitor. See all the alarms going off 🙂

The design is inspired by Philips Intellivue. The alarm sounds I took from their website 😉

In the rest of this post I want to discuss how I came to this result.

Devices

The DIY ECG from last post was a good basis (https://www.tumblr.com/medical89/650543279114469376/diy-wireless-ecg?source=share).

I got a BP with bluetooth capabilities (https://www.medisana.com/en/Health-control/Blood-pressure-monitor/BU-540-connect-Upper-arm-blood-pressure-monitor.html)

And a pulseoximeter with bluetooth (https://de.aliexpress.com/item/1005005549153646.html)

I reverse engineered (aka hacked) both of their bluethooth communication to get the live data into my website instead of their apps. I.e., get the BP after it was measured or retrieve the oxygen concentration every second. Then I extended my ECG application and it's web interface to include this information.

Alarms

The application now also includes alarms, just like a real patient monitor. Cyan alarms are triggered if a device is not connected correctly, red alarms if a vital value is outside of its limits!

Buttons

I also wired up the power button on the BP to my ECG so I can start it from the website using the BP button. When entering a number in the text field next to the button, the BP is taken automatically every x seconds 🙂

The shock button is wired up to a TENS unit and can give shocks.

I also made a program that can sync shocks and BP inflates to a video, but that's a story for another day!

In the last year I came up with an improved version of my DIY ECG (https://medical89.tumblr.com/post/182956958882/diy-ecg-part-1). It can be used wirelessly and is even easier to build and operate.

As in my last project, I still use the AD8232 chip as single lead ECG. However, this time it is combined with a much more powerful micro controller, the ESP32. This micro-controller is capable to create a WIFI hotspot or connect to your home WIFI.

Ordering Components

Here are the links to purchase the components on Aliexpress:

ESP32: https://www.aliexpress.com/item/1005001635370174.html

AD8232: https://www.aliexpress.com/item/33007711518.html

Jumper wires (10cm, 20pin): https://www.aliexpress.com/item/4000419476085.html

Electrodes: https://www.aliexpress.com/item/4000052854233.html

For US citizens, I also have Amazon links:

ESP32: https://www.amazon.com/dp/B0718T232Z

AD8232: https://www.amazon.com/dp/B0722Y8YC6

Jumper wires (3.9inch): https://www.amazon.com/dp/B07GD2BWPY

Electrodes: https://www.amazon.com/dp/B06X1CL4S6

The total cost including shipping (to Europe) via Aliexpress is less than 35$. Via Amazon it is less than 44$ (including the electrodes).

Connecting Components

Wiring up the components is really easy. You only need to connect 3 pins with the jumper wires.

ESP32 -> AD8232

GND -> GND

3v3 -> 3.3v

P34 (or G34) -> OUTPUT

You can now test the ECG by powering up the ESP32 via a micro USB cable. Connect the electrode cable and place the pads as described in my last build (https://medical89.tumblr.com/post/182977403082/diy-ecg-part-3). You can see the output on the small red LED on the AD8232.

Warning: To be on the safe side, never plug your Arduino into a device powered from the grid!! Plug it in your laptop or a power bank instead.

Software

To program the ESP32 you first need to connect it to your computer via a micro USB cable. As with my last project, I am using the Arduino IDE (https://www.arduino.cc/en/software) to program the ESP32 micro controller. Install it and then follow the guide here (https://randomnerdtutorials.com/installing-the-esp32-board-in-arduino-ide-windows-instructions/) to install the ESP32 development tools. You can also test your installation as described on the website.

Programming

Download the ECG code I wrote (https://mega.nz/file/1nYkCDxY#2cPttxzplUQxMGIHJf6gDoOK9JDr234J-BEkRcrweXE) and open the .ino file in the Arduino IDE. Press the "Upload" button in the Arduino IDE (second symbol, arrow pointing to the right). If everything went right, there is a new WIFI called "ESP32" with password "I<3DiyECGs". Connect to the WIFI. By accessing the website http://192.168.4.1 on the device, you can stream the ECG's output. Note, if you are on a phone, disable "mobile data" if the website is not displayed.

Final Result

This is me using it:

Has anyone actually built their own ECG based on my guide (https://medical89.tumblr.com/post/182956958882/diy-ecg-part-1)?

Part 1 Part 2 Part 3

Software

The last part of this tutorial is about the software needed to display the ECG signal on your computer. This guide is based on the tutorial found on Sparkfun (https://learn.sparkfun.com/tutorials/ad8232-heart-rate-monitor-hookup-guide/all). If you are stuck at some point in this tutorial, I would recommend you to read the section on Sparkfun, as their guide is more detailed.

Three pieces of software are needed:

Arduino IDE (https://www.arduino.cc/en/Main/Software)

Processing IDE (https://processing.org/download/)

the adapted code (https://mega.nz/#!9roDGAha!21aKPDvBIuEhjTG9IAFJlwZZrH9vBTv6E5AQN-6GP2g)

Install the version of the Arduino IDE and Processing IDE for your operating system. For the Arduino board to be recognized by Windows, one needs to install an additional driver. Refer to this site for the detailed installation instructions. I would also recommend you to get familiar with the interface and try to upload the first demo program as described under "Launch and Blink!" on the same page. Note: for Tools->Board you would choose "Arduino Nano", for Tools->Processor "ATmega 328p (old bootloader)" and for Tools->Port you would try out all options until it works!

If that worked, we can now upload the code for the ECG. Extract the zip archive with the code and open up "Heart_Rate_Display_Arduino.ino" in the "Heart_Rate_Display_Arduino" folder with the Arduino IDE. Make sure the options under Tools are set to the same values as before. Note: The port can change over time, especially if unplugging the Arduino at some time! The ECG can already be tested. Make sure, the ECG electrodes are placed correctly on your body (see last part 3 of this tutorial). Now open the Serial plotter under the Tools menu in the Arduino IDE. The "baud rate" should be set to the value 19200. This is the rate at which Arduino and computer communicate. If everything was done correctly, you should already see something very much like an ECG!

For a fancier output, open up the Processing IDE. Open the "Heart_Rate_Display_Processing.pde" file from the "Heart_Rate_Display_Processing" folder. For sound output (yes, the beeping of the ECG!) an extra programming library is needed. Go to Tools->Add Tool and there to the Libraries tab. Search for "minim" and click on the Install button on the lower left corner of the window. After it is installed, close the window. Then run the code by pressing the Play button in the main window. Probably it will crash on the first try. Increment the zero found in the code at the line with "myPort = new Serial(this, Serial.list()[0], 19200);" and try again. By doing so, one searches for the Arduino as before in the Arduino IDE. Repeat the process until it works. The correct number should be probably under 10.

If you did everything correctly, the output should look somewhat like this:

Part 1 Part 2 Part 4

Disclaimer: Only follow the steps below, if you are sure what you are doing!

The Build

When you got all your the components, solder on the pins headers (if they are not already on). On my AD8232 the headphone jack (where the leads are plugged in later) was loose and I had to make proper solder connections there too.

Next you can connect the AD8232 to the Arduino in following way (see the Sparkfun tutorial for reference: https://learn.sparkfun.com/tutorials/ad8232-heart-rate-monitor-hookup-guide).

AD8232 -> Arduino -------------------------------------------------

GND -> GND

3.3v -> 3.3v

OUTPUT -> A0

LO- -> D11

LO+ -> D10

SDN Shutdown -> Not used

This connections can be done directly with the jumperwires (if you ordered them). Just separate five jumperwires from the rest of the pack and simply connect the pins as described above.

The more elegant way is to do it on a breadboard. On a breadboard the pins are connected by default as shown in the image below. The inner pins are connected vertically, the other ones horizontally.

I came up with following wiring for the AD8232. With the knowledge from the last illustration the wiring can be verified.

One can now try out the ECG circuit without any software! As I said, the AD8232 is a standalone single lead ECG and it can show the heartbeat on the LED directly on the circuit board. The Arduino is just used as a power supply. I can now be plugged into your laptop.

Warning: To be on the safe side, never plug your Arduino into a device powered from the grid!! Use a battery powered laptop instead!!

The electrodes can be placed like this:

For me the right placement produced really good results. Moving the upper electrodes nearer to the heart produced strange results. Beware, that the correct electrode must be at the correct position. E.g. when switching left and right the ECG is flipped, when using the bottom electrode near the heart, the trace looks not correct. Usually the electrodes have letters on them (L and R), that indicate, if they are on the left or right side.

Part 1 Part 3 Part 4

Disclaimer: Only attempt the build if you know what you are doing!

Shopping list:

Arduino Nano with USB mini cable (https://www.ebay.com/itm/201539955347)

AD8232 module with 3 ECG leads and pads (https://www.ebay.com/itm/401249773691)

small Breadboard (https://www.ebay.com/itm/372133400247) + Wiring (https://www.ebay.com/itm/183609770050) alternative: jumper wires (https://www.ebay.com/itm/311660166123)

ECG electrodes (https://www.ebay.com/itm/401471154994)

This all adds up to less than 20$. Beware, that shipping from China (to e.g. the EU) can take more than 30 days… If you want your items faster, look for them in a local electronics store, a local reseller’s website or Amazon.

Although the assembly on the breadboard (or with the jumper wires) is solderless, there could be some soldering required… When I ordered my Arduino, the pin headers were not attached like in this listing (https://www.ebay.com/itm/401352746462) and the headphone jack on the AD8232 was loose…

Part 2 Part 3 Part 4

My medical fetish has always been more on the technical side. As medical devices are quite expensive, I made myself the quest to build them on the cheap. Since electronics is not my primary field of expertise (but software is), I would often just buy cheap circuits from ebay. I would then modify existing software to my special needs ;) For my first tumblr post I would like to tell you about my latest acquisition. It's a single lead ECG circuit that can be plugged into a computer! Here is the final product:

The output of the software looks like this:

My build is based on the AD8232 chip, which is actually a complete single lead ECG! It is distributed by Sparkfun, a great retailer for those kinds of integrated circuits (ICs). The AD8232 is then connected to a so-called Arduino board, a very popular micro controller. The Arduino can communicate over USB with your computer.

There is actually a whole guide and buying list (about 75$) on the Sparkfun website.