Android Based Wireless ECG

ECG

The title of [Nuclearrambo’s] post says it all, “Android based wireless ECG monitoring (Temperature sensor and glucometer included).” Wow! What a project!

The project is built around the HC-06 bluetooth module and the Stellaris LaunchPad from TI, an inexpensive ARM developer kit. Building an ECG is a great way to learn about instrumentation amplifiers, a type of differential amplifier used for its extremely high common mode rejection ratio (CMRR). Please be sure to keep in mind that there are a myriad of safety issues and regulation concerns for medical device, and there is no doubt that an ECG is considered a medical device. Sadly, [Nuclearrambo’s] post does not include all of the code and design files you need to build the system, which is understandable considering this is a medical device. That being said, he provides a lot of information about building high-quality ECG instrumentation and the web interface.

It would be great if [Nuclearrambo] could post the Android application code and Stellaris LaunchPad code. Even with these omissions, this post is still worth reading. Designing medical devices requires a lot of know-how, but who knows, maybe your next project can save your life!

Arduino Powered ECG Informs Users of Their Death

Just when you thought you’d seen an Arduino do everything, [birdyberth] built an Arduino powered Electrocardiogram (ECG or EKG). Electrocardiography is a non invasive method of studying the heart. For many of us that means a 10 minute test during our yearly physical exam. Medical grade ECGs can use up to 10 electrodes. To keep things simple [birdyberth] went the route of a few circuits we’ve seen before, and reduced it to two electrodes and a ground reference. [birdyberth] makes note that the circuit is only safe if battery power is used.

The “heart” of any ECG is an instrumentation amplifier. Instrumentation amplifiers can be thought of as super differential amplifiers. They have buffered inputs, low DC offset, low drift, low noise, high open loop gain, and high impedance among other favorable characteristics. The downside is cost. A typical op amp might cost 0.50 USD in single piece quantities. Instrumentation amplifiers, like [birdyberth’s] INA128 can cost $8.30 or (much) more each. The extra cost is understandable when one thinks about the signals being measured. The ECG is “picking up” the heart’s electrical signals from the outside on skin. On commonly used ECG graph paper, a 1mm square translates to about .1 mV. High gain and clean signals are really needed to get any meaningful data here.

Electrodes are another important part of an ECG. Medical grade ECG units typically use disposable adhesive electrodes that make a strong electrical connection to the skin, and hurt like heck when they’re ripped off by the nurse. [birdyberth] was able to make electrodes using nothing more than tin foil and paper clips. We think the real trick is in the shower gel he used to make an electrical connection to his skin. While messy, the gel provides a low resistance path for the tiny currents to flow.

The actual processing in [birdyberth’s] circuit is easy to follow. The signal from the instrumentation amplifier is sent through a low pass filter, through a 741 op amp, and then on to the Arduino. The Arduino uses a 16×2 LCD to display heart rate in beats per minute, along with a friendly message informing you if you are alive or dead. The circuit even provides audible feedback for heart beats, and the classic “flatline tone” when the users either disconnects the electrodes or expires. [birdyberth] has also plugged in his pocket oscilloscope just after the low pass filter. As his video shows, the familiar ECG waveform is clearly visible. We’d love to see a more complex version of this hack combined with [Addie’s] heart simulator, so we could know exactly which heart malady is killing us in real time!

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DIY Propeller-based ECG

propeller_ecg

[Ray] likes to build all sorts of Propeller-based projects, but one of the more interesting items we came across was this DIY ECG. While we have covered other DIY electrocardiograms before, he left the breadboard behind and put together a nicely done PCB for his build.

The ECGs design should be pretty familiar to anyone that has seen our ECG coverage in the past. The user places his thumbs on the large built-in pads, which allow the circuit to sense the electrical signals produced by heart’s contractions. These small electrical impulses are then amplified using an AD627 instrument amplifier before being further amplified via a dual op-amp.

The amplified signal is filtered and then fed into the Propeller’s ADC, which displays the user’s heart rhythms via an LED. The data can also be fed into a computer via an optoisolated serial connection.

[Ray] lays out a litany of warnings and precautions that should be followed before downloading his schematics and firmware. We have to echo those warnings, as it doesn’t take a large well-placed shock to disrupt the heart.

Wireless electrocardiography… with iPhone

This module is a sensor package for monitoring the electrical activity of the heart. It is the product of an effort to create a Wireless Body Sensor Network node that is dependable while consuming very little electricity, which means a longer battery life. To accomplish this, the microcontroller in charge of the node compresses the data (not usually done with wireless ECG hardware) so that the radio transmissions are as short and infrequent as possible.

[Igor] sent us this tip and had a short question and answer session with one of the developers. It seems they are working with the MSP430 chips right now because of their low power consumption. Unfortunately those chips still draw a high load when transmitting so future revisions will utilize an alternative.

Oh, and why the iPhone? The device that displays the data makes little difference. In this case they’re transmitting via Bluetooth for a real-time display (seen in the video after the break). This could be used for a wide variety of devices, or monitored remotely via the Internet.

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