DIY ECG Machine On The Cheap
6,809 words | Posted on August 14th, 2009
Scott was 23.89 years old when he wrote this!
Filed under: Circuitry, DIY ECG, General, Microcontrollers, Python
| Note from the Author: This page documents how I made an incredibly simple ECG machine with a minimum of parts to view the electrical activity of my own heart. Feel free to repeat my experiment, but do so at your own risk. There are similar projects floating around on the internet, but I aim to provide a more complete, well-documented, and cheaper solution, with emphasis on ECG processing and analysis, rather than just visualization. If you have any questions or suggestions please contact me. Also, if you attempt this project yourself I’d love to post your results! Good luck! –Scott |
Background
You’ve probably seen somebody in a hospital setting hooked up to a big mess of wires used to analyze their heartbeat. 
The goal of such a machine (called an electrocardiograph, or ECG) is to amplify, measure, and record the natural electrical potential created by the heart. Note that cardiac electrical signals are different than heart sounds, which are listened to with a stethoscope. The intrinsic cardiac pacemaker system is responsible for generating these electrical signals which serve to command and coordinate contraction of the four chambers at the heart at the appropriate intervals [atria (upper chambers) first, then the ventricles (lower chambers) a fraction of a second later], and their analysis reveals a wealth of information about cardiac regulation, as well insights into pathological conditions. Each heartbeat produces a similar pattern in the ECG signal, called a PQRST wave. 
[picture] The smooth curve in the ECG (P) is caused by the stimulation of the atria via the Sinoatrial (SA) node in the right atrium. There is a brief pause, as the electrical impulse is slowed by the Atrioventricular (AV) node and Purkinje fibers in the bundle of His. The prominent spike in the ECG (the QRS complex) is caused by this step, where the electrical impulse travels through the inter-ventricular septum and up through the outer walls of the ventricles. The sharp peak is the R component, and exact heart rate can be calculated as the inverse of the R-to-R interval (RRi). Fancy, huh?
Project Goal
The goal of this project is to generate an extremely cheap, functional ECG machine made from common parts, most of which can be found around your house. This do-it-yourself (DIY) ECG project is different than many others on the internet in that it greatly simplifies the circuitry by eliminating noise reduction components, accomplishing this via software-based data post-processing. Additionally, this writeup is intended for those without any computer, electrical, or biomedical experience, and should be far less convoluted than the suspiciously-cryptic write-ups currently available online. In short, I want to give everybody the power to visualize and analyze their own heartbeat!
The ECG of my own heart:
Video Overview
I know a lot of Internet readers aren’t big fans of reading. Therefore, I provided an outline of the process in video form. Check out the videos, and if you like what you see read more!
Video 1/3: Introducing my ECG machine
Video 2/3: Recording my ECG
Video 3/3: Analyzing my ECG
Electrical Theory
Measurement: The electrical signals which command cardiac musculature can be detected on the surface of the skin. In theory one could grab the two leads of a standard volt meter, one with each hand, and see the voltage change as their heart beats, but the fluctuations are rapid and by the time these signals reach the skin they are extremely weak (a few millionths of a volt) and difficult to detect with simple devices. Therefore, amplification is needed.
Amplification: A simple way to amplify the electrical difference between two points is to use a operational amplifier, otherwise known as an op-amp. The gain (multiplication factor) of an op-amp is controlled by varying the resistors attached to it, and an op-amp with a gain of 1000 will take a 1 millivolt signal and amplify it to 1 volt. There are many different types of microchip op-amps, and they’re often packaged with multiple op-amps in one chip (such as the quad-op-amp lm324, or the dual-op-amp lm358n). Any op-amp designed for low voltage will do for our purposes, and we only need one.
Noise: Unfortunately, the heart is not the only source of voltage on the skin. Radiation from a variety of things (computers, cell phones, lights, and especially the wiring in your walls) is absorbed by your skin and is measured with your ECG, in many cases masking your ECG in a sea of electrical noise. The traditional method of eliminating this noise is to use complicated analog circuitry, but since this noise has a characteristic, repeating, high-frequency wave pattern, it can be separated from the ECG (which is much slower in comparison) using digital signal processing computer software!
Digitization: Once amplified, the ECG signal along with a bunch of noise is in analog form. You could display the output with an oscilloscope, but to load it into your PC you need an analog-to-digital converter. Don’t worry! If you’ve got a sound card with a microphone input, you’ve already got one! It’s just that easy. We’ll simply wire the output of our ECG circuit to the input of our sound card, record the output of the op-amp using standard sound recording software, remove the noise from the ECG digitally, and output gorgeous ECG traces ready for visualization and analysis!
Parts/Cost
I’ll be upfront and say that I spent $0.00 making my ECG machine, because I was able to salvage all the parts I needed from a pile of old circuit boards. If you need specific components, check your local RadioShack. If that’s a no-go, hit-up Digikey (it’s probably cheaper too). Also, resistor values are flexible. Use mine as a good starter set, and vary them to suit your needs. If you buy everything from Digikey, the total cost of this project would be about $1. For now, here’s a list of all the parts you need:
Making the Device
Keep in mind that I’m not an electrical engineer (I have a masters in molecular biology but I’m currently a dental student if you must know) and I’m only reporting what worked well for me. I don’t claim this is perfect, and I’m certainly open for (and welcome) suggestions for improvement. With that in mind, here’s what I did!
This is pretty much it. First off is a power source. If you want to be safe, use three AAA batteries in series. If you’re a daredevil and enjoy showing off your ghettorigging skills, do what I did and grab 5v from a free USB plug! Mua ha ha ha. The power goes into the circuit and so do the leads/electrodes connected to the body. You can get pretty good results with only two leads, but if you want to experiment try hooking up an extra ground lead and slap it on your foot. More on the electrodes later. The signal from the leads is amplified by the circuit and put out the headphone cable, ready to enter your PC’s sound card through the microphone jack!
Note how I left room in the center of the circuit board. That was intentional! I wanted to expand this project by adding a microcontroller to do some on-board, real-time analysis. Specifically, an ATMega8! I never got around to it though. Its purpose would be to analyze the output of the op-amp and graph the ECG on a LCD screen, or at least measure the time between beats and display HR on a screen. (More ideas are at the bottom of this document.) Anyway, too much work for now, maybe I’ll do it one day in the future.
ECG circuit diagram:
This is the circuit diagram. This is a classical high-gain analog differential amplifier. It just outputs the multiplied difference of the inputs. The 0.1uF capacitor helps stabilize the signal and reduce high frequency noise (such as the audio produced by a nearby AM radio station). Use Google if you’re interested in learning exactly how it works.
ECG schematic:
This is how I used my LM358N to create the circuit above. Note that there is a small difference in my board from the photos and this diagram. This diagram is correct, but the circuit in some of the pictures is not. Briefly, when I built it I accidentally connected the (-) lead directly to ground, rather than to the appropriate pin on the microchip. This required me to place a 220kOhm between the leads to stabilize the signal. I imagine if you wire it CORRECTLY (as shown in these circuit diagrams) it will work fine, but if you find it too finicky (jumping quickly from too loud to too quiet), try tossing in a high-impedance resistor between the leads like I did. Overall, this circuit is extremely flexible and I encourage you to build it on a breadboard and try different things. Use this diagram as a starting point and experiment yourself!
The Electrodes:
You can make electrodes out of anything conductive. The most recent graphs were created from wires with gator clips on them clamping onto pennies (pictured). Yeah, I know I could solder directly to the pennies (they’re copper) but gator clips are fast, easy, and can be clipped to different materials (such as aluminum foil) for testing. A dot of moisturizing lotion applied to the pennies can be used to improve conduction between the pennies and the skin, but I didn’t find this to be very helpful. If pressed firmly on the body, conduction seems to be fine. Oh! I just remembered. USE ELECTRICAL TAPE TO ATTACH LEADS TO YOUR BODY! I tried a million different things, from rubber bands to packaging tape. The bottom line is that electrical tape is stretchy enough to be flexible, sticky enough not to fall off (even when moistened by the natural oils/sweat on your skin), and doesn’t hurt that bad to peel off.
Some of the best electrodes I used were made from aluminum cans! Rinse-out a soda can, cut it into “pads”, and use the sharp edge of a razor blade or pair of scissors to scrape off the wax coating on all contact surfaces. Although a little unconformable and prone to cut skin due to their sharp edges, these little guys work great!
Hooking it Up
This part is the most difficult part of the project! This circuit is extremely finicky. The best way to get it right is to open your sound editor (In Windows I use GoldWave because it’s simple, powerful, and free, but similar tools exist for Linux and other Unix-based OSes) and view the low-frequency bars in live mode while you set up. When neither electrode is touched, it should be relatively quiet. When only the + electrode is touched, it should go crazy with noise. When you touch both (one with each hand) the noise should start to go away, possibly varying by how much you squeeze (how good of a connection you have). The whole setup process is a game between too much and too little conduction. You’ll find that somewhere in the middle, you’ll see (and maybe hear) a low-frequency burst of noise once a second corresponding to your heartbeat. [note: Did you know that's how the second was invented? I believe it was ] Once you get that good heartbeat, tape up your electrodes and start recording. If you can’t get it no matter what you do, start by putting the ground electrode in your mouth (yeah, I said it) and pressing the + electrode firmly and steadily on your chest. If that works (it almost always does), you know what to look for, so keep trying on your skin. For short recordings (maybe just a few beats) the mouth/chest method works beautifully, and requires far less noise reduction (if any), but is simply impractical for long-term recordings. I inside vs. outside potential is less susceptible to noise-causing electrical radiation. Perhaps other orifices would function similarly? I’ll leave it at that. I’ve also found that adding a third electrode (another ground) somewhere else on my body helps a little, but not significantly. Don’t give up at this step if you don’t get it right away! If you hear noise when + is touched, your circuit is working. Keep trying and you’ll get it eventually.
Recording the ECG
This is the easy part. Keep an eye on your “bars” display in the audio program to make sure something you’re doing (typing, clicking, etc) isn’t messing up the recording. If you want, try surfing the net or playing computer games to see how your heart varies. Make sure that as you tap the keyboard and click the mouse, you’re not getting noise back into your system. If this is a problem, try powering your device by batteries (a good idea for safety’s sake anyway) rather than another power source (such as USB power). Record as long as you want! Save the file as a standard, mono, wave file.
Digitally Eliminating Noise
Now it’s time to clean-up the trace. Using GoldWave, first apply a lowpass filter at 30 Hz. This kills most of your electrical noise (> 30hz), while leaving the ECG intact (< 15Hz). However, it dramatically decreases the volume (potential) of the audio file. Increase the volume as necessary to maximize the window with the ECG signal. You should see clear heartbeats at this point. You may want to apply an auto-gain filter to normalize the heartbeats potentials. Save the file as a raw sound file (.snd) at 1000 Hz (1 kHz) resolution.
Presentation and Analysis
Now you’re ready to analyze! Plop your .snd file in the same folder as my [ecg.py script], edit the end of the script to reflect your .snd filename, and run the script by double-clicking it. (Keep in mind that my script was written for python 2.5.4 and requires numpy 1.3.0rc2 for python 2.5, and matplotlib 0.99 for python 2.5 – make sure you get the versions right!) Here’s what you’ll see!
This is a small region of the ECG trace. The “R” peak is most obvious, but the details of the other peaks are not as visible. If you want more definition in the trace (such as the blue one at the top of the page), consider applying a small collection of customized band-stop filters to the audio file rather than a single, sweeping lowpass filter. Refer to earlier posts in the DIY ECG category for details. Specifically, code on Circuits vs. Software for noise reduction entry can help. For our purposes, calculating heart rate from R-to-R intervals (RRIs) can be done accurately with traces such as this.
Your heart rate fluctuates a lot over time! By plotting the inverse of your RRIs, you can see your heart rate as a function of time. Investigate what makes it go up, go down, and how much. You’d be surprised by what you find. I found that checking my email raises my heart rate more than first-person-shooter video games. I get incredibly anxious when I check my mail these days, because I fear bad news from my new university (who knows why, I just get nervous about it). I wonder if accurate RRIs could be used to assess nervousness for the purposes of lie detection?
This is the RRI plot where the value of each RRI (in milliseconds) is represented for each beat. It’s basically the inverse of heart rate. Miscalculated heartbeats would show up as extremely high or extremely low dots on this graph. However, excluding points above or below certain bounds means that if your heart did double-beat, or skip a beat, you wouldn’t see it. Note that I just realized my axis label is wrong (it should be sec, not ms). Oh well =o\
A Poincare Plot is a commonly-used method to visually assess heart rate variability as a function of RRIs. In this plot, each RRI is plotted against the RRI of the next subsequent beat. In a heart which beats at the same speed continuously, only a single dot would be visible in the center. In a heart which beats mostly-continuously, and only changes its rate very slowly, a linear line of dots would be visible in a 1:1 ratio. However, in real life the heart varies RRIs greatly from beat to beat, producing a small cloud of dots. The size of the cloud corresponds to the speed at which the autonomic nervous system can modulate heart rate in the time frame of a single beat.
The frequency of occurrence of various RRIs can be expressed by a histogram. The center peak corresponds to the standard heart rate. Peaks to the right and left of the center peak correspond to increased and decreased RRIs, respectively. A gross oversimplification of the interpretation of such data would be to state that the upper peak represents the cardio-inhibitory parasympathetic autonomic nervous system component, and the lower peak represents the cardio-stimulatory sympathetic autonomic nervous system component.
Taking the Fast Fourier Transformation of the data produces a unique trace whose significance is extremely difficult to interpret. Near 0Hz (infinite time) the trace heads toward ∞ (infinite power). To simplify the graph and eliminate the near-infinite, low-frequency peak we will normalize the trace by multiplying each data point by its frequency, and dividing the vertical axis units by Hz to compensate. This will produce the following graph…
This is the power spectrum density (PSD) plot of the ECG data we recorded. Its physiological interpretation is extraordinarily difficult to understand and confirm, and is the subject of great debate in the field of autonomic neurological cardiac regulation. An oversimplified explanation of the significance of this graph is that the parasympathetic (cardio-inhibitory) branch of the autonomic nervous system works faster than the sympathetic (cardio-stimulatory) branch. Therefore, the lower peak corresponds to the sympathetic component (combined with persistent parasympathetic input, it’s complicated), while the higher-frequency peak corresponds to the parasympathetic component, and the sympathetic/parasympathetic relationship can be assessed by the ratio of the integrated areas of these peaks after a complicated curve fitting processes which completely separates overlapping peaks. To learn more about power spectral analysis of heart rate over time in the frequency domain, I recommend skimming this introduction to heart rate variability website and the article on Heart Rate Variability following Myocardial Infarction (heart attack). Also, National Institute of Health (NIH) funded studies on HRV should be available from pubmed.org. If you want your head to explode, read Frequency-Domain Characteristics and Filtering of Blood Flow Following the Onset of Exercise: Implications for Kinetics Analysis for a lot of good frequency-domain-analysis-related discussion and rationalization.
Encouraging Words:
Please, if you try this don’t die. The last thing I want is to have some kid calling me up and yelling at me that he nearly electrocuted himself when he tried to plug my device directly into a wall socket and now has to spend the rest of his life with two Abraham Lincolns tattooed onto his chest resembling a second set of nipples. Please, if you try this use common sense, and of course you’re responsible for your own actions. I provide this information as a description of what I did and what worked for me. If you make something similar that works, I’ve love to see it! Send in your pictures of your circuit, charts of your traces, improved code, or whatever you want and I’ll feature it on the site. GOOD LUCK!
Fancier Circuit:
If you want to try this, go for it! Briefly, this circuit uses 6 op-amps to help eliminate effects of noise. It’s also safer, because of the diodes interconnecting the electrodes. It’s the same circuit as on [this page].
Last minute thoughts:
- More homemade ECG information can be found on my earlier posts in the DIY ECG category, however this page is the primary location of my most recent thoughts and ideas.
- You can use moisturizing lotion between the electrodes and your skin to increase conduction. However, keep in mind that better conduction is not always what you want. You’ll have to experiment for yourself.
- Variation in location of electrodes will vary the shape of the ECG. I usually place electrodes on each side of my chest near my arms. If your ECG appears upside-down, reverse the leads!
- Adding extra leads can improve grounding. Try grounding one of your feet with a third lead to improve your signal. Also, if you’re powering your device via USB power consider trying battery power – it should be less noisy.
- While recording, be aware of what you do! I found that if I’m not well-grounded, my ECG is fine as long as I don’t touch my keyboard. If I start typing, every keypress shows up as a giant spike, bigger than my heartbeat!
- If you get reliable results, I wonder if you could make the device portable? Try using a portable tape recorder, voice recorder, or maybe even minidisc recorder to record the output of the ECG machine for an entire day. I haven’t tried it, but why wouldn’t it work? If you want to get fancy, have a microcontroller handle the signal processing and determine RRIs (should be easy) and save this data to a SD card or fancy flash logger.
- The microcontroller could output heart rate via the serial port.
- If you have a microcontroller on board, why not display heart rate on a character LCD?
- While you have a LCD on there, display the ECG graphically!
- Perhaps a wireless implementation would be useful.
- Like, I said, there are other, more complicated analog circuits which reduce noise of the outputted signal. I actually built Jason Nguyen’s fancy circuit which used 6 op-amps but the result wasn’t much better than the simple, 1 op-amp circuit I describe here once digital filtering was applied.
- Arrhythmic heartbeats (where your heart screws-up and misfires, skips a beat, double-beats, or beats awkwardly) are physiological (normal) and surprisingly common. Although shocking to hear about, sparse, single arrhythmic heartbeats are normal and are a completely different ball game than chronic, potentially deadly heart arrhythmias in which every beat is messed-up. If you’re in tune with your body, you might actually feel these occurrences happening. About three times a week I feel my heart screw up a beat (often when it’s quiet), and it feels like a sinking feeling in my chest. I was told by a doctor that it’s totally normal and happens many times every day without me noticing, and that most people never notice these single arrhythmic beats. I thought it was my heart skipping a beat, but I wasn’t sure. That was my motivation behind building this device – I wanted to see what my arrhythmic beats looked like. It turns out that it’s more of a double-beat than a skipped beat, as observed when I captured a single arrhythmic heartbeat with my ECG machine, as described in this entry.
- You can improve the safety of this device by attaching diodes between leads, similar to the more complicated circuit. Theory is that if a huge surge of energy does for whatever reason get into the ECG circuit, it’ll short itself out at the circuit level (conducting through the diodes) rather than at your body (across your chest / through your heart).
- Alternatively, use an AC opto-isolator between the PC sound card and the ECG circuit to eliminate the possibility of significant current coming back from the PC.
- On the Hackaday post, Flemming Frandsen noted that an improperly grounded PC could be dangerous because the stored charge would be manifest in the ground of the microphone jack. If you were to ground yourself to true ground (using a bench power supply or sticking your finger in the ground socket of an AC wall plug) this energy could travel through you! So be careful to only ground yourself with respect to the circuit using only battery power to minimize this risk.
- Do not attempt anything on this page. Ever. Don’t even read it. You read it already! You’re sill reading it aren’t you? Yeah. You don’t follow directions well do you?
SAMPLE FILTERED RECORDING:
I think this is the same one I used in the 3rd video from my single op-amp circuit. [scottecg.snd] It’s about an hour long, and in raw sound format (1000 Hz). It’s already been filtered (low-pass filtered at 30Hz). You can use it with my code below!
CODE
print "importing libraries..."
import numpy, pylab
print "DONE"
class ECG:
def trim(self, data,degree=100):
print 'trimming'
i,data2=0,[]
while i<len(data):
data2.append(sum(data[i:i+degree])/degree)
i+=degree
return data2
def smooth(self,list,degree=15):
mults=[1]
s=[]
for i in range(degree): mults.append(mults[-1]+1)
for i in range(degree): mults.append(mults[-1]-1)
for i in range(len(list)-len(mults)):
small=list[i:i+len(mults)]
for j in range(len(small)):
small[j]=small[j]*mults[j]
val=sum(small)/sum(mults)
s.append(val)
return s
def smoothWindow(self,list,degree=10):
list2=[]
for i in range(len(list)):
list2.append(sum(list[i:i+degree])/float(degree))
return list2
def invertYs(self):
print 'inverting'
self.ys=self.ys*-1
def takeDeriv(self,dist=5):
print 'taking derivative'
self.dys=[]
for i in range(dist,len(self.ys)):
self.dys.append(self.ys[i]-self.ys[i-dist])
self.dxs=self.xs[0:len(self.dys)]
def genXs(self, length, hz):
print 'generating Xs'
step = 1.0/(hz)
xs=[]
for i in range(length): xs.append(step*i)
return xs
def loadFile(self, fname, startAt=None, length=None, hz=1000):
print 'loading',fname
self.ys = numpy.memmap(fname, dtype='h', mode='r')*-1
print 'read %d points.'%len(self.ys)
self.xs = self.genXs(len(self.ys),hz)
if startAt and length:
self.ys=self.ys[startAt:startAt+length]
self.xs=self.xs[startAt:startAt+length]
def findBeats(self):
print 'finding beats'
self.bx,self.by=[],[]
for i in range(100,len(self.ys)-100):
if self.ys[i]<15000: continue # SET THIS VISUALLY
if self.ys[i]<self.ys[i+1] or self.ys[i]<self.ys[i-1]: continue
if self.ys[i]-self.ys[i-100]>5000 and self.ys[i]-self.ys[i+100]>5000:
self.bx.append(self.xs[i])
self.by.append(self.ys[i])
print "found %d beats"%(len(self.bx))
def genRRIs(self,fromText=False):
print 'generating RRIs'
self.rris=[]
if fromText: mult=1
else: 1000.0
for i in range(1,len(self.bx)):
rri=(self.bx[i]-self.bx[i-1])*mult
#if fromText==False and len(self.rris)>1:
#if abs(rri-self.rris[-1])>rri/2.0: continue
#print i, "%.03f\t%.03f\t%.2f"%(bx[i],rri,60.0/rri)
self.rris.append(rri)
def removeOutliers(self):
beatT=[]
beatRRI=[]
beatBPM=[]
for i in range(1,len(self.rris)):
#CHANGE THIS AS NEEDED
if self.rris[i]<0.5 or self.rris[i]>1.1: continue
if abs(self.rris[i]-self.rris[i-1])>self.rris[i-1]/5: continue
beatT.append(self.bx[i])
beatRRI.append(self.rris[i])
self.bx=beatT
self.rris=beatRRI
def graphTrace(self):
pylab.plot(self.xs,self.ys)
#pylab.plot(self.xs[100000:100000+4000],self.ys[100000:100000+4000])
pylab.title("Electrocardiograph")
pylab.xlabel("Time (seconds)")
pylab.ylabel("Potential (au)")
def graphDeriv(self):
pylab.plot(self.dxs,self.dys)
pylab.xlabel("Time (seconds)")
pylab.ylabel("d/dt Potential (au)")
def graphBeats(self):
pylab.plot(self.bx,self.by,'.')
def graphRRIs(self):
pylab.plot(self.bx,self.rris,'.')
pylab.title("Beat Intervals")
pylab.xlabel("Beat Number")
pylab.ylabel("RRI (ms)")
def graphHRs(self):
#HR TREND
hrs=(60.0/numpy.array(self.rris)).tolist()
bxs=(numpy.array(self.bx[0:len(hrs)])/60.0).tolist()
pylab.plot(bxs,hrs,'g',alpha=.2)
hrs=self.smooth(hrs,10)
bxs=bxs[10:len(hrs)+10]
pylab.plot(bxs,hrs,'b')
pylab.title("Heart Rate")
pylab.xlabel("Time (minutes)")
pylab.ylabel("HR (bpm)")
def graphPoincare(self):
#POINCARE PLOT
pylab.plot(self.rris[1:],self.rris[:-1],"b.",alpha=.5)
pylab.title("Poincare Plot")
pylab.ylabel("RRI[i] (sec)")
pylab.xlabel("RRI[i+1] (sec)")
def graphFFT(self):
#PSD ANALYSIS
fft=numpy.fft.fft(numpy.array(self.rris)*1000.0)
fftx=numpy.fft.fftfreq(len(self.rris),d=1)
fftx,fft=fftx[1:len(fftx)/2],abs(fft[1:len(fft)/2])
fft=self.smoothWindow(fft,15)
pylab.plot(fftx[2:],fft[2:])
pylab.title("Raw Power Sprectrum")
pylab.ylabel("Power (ms^2)")
pylab.xlabel("Frequency (Hz)")
def graphFFT2(self):
#PSD ANALYSIS
fft=numpy.fft.fft(numpy.array(self.rris)*1000.0)
fftx=numpy.fft.fftfreq(len(self.rris),d=1)
fftx,fft=fftx[1:len(fftx)/2],abs(fft[1:len(fft)/2])
fft=self.smoothWindow(fft,15)
for i in range(len(fft)):
fft[i]=fft[i]*fftx[i]
pylab.plot(fftx[2:],fft[2:])
pylab.title("Power Sprectrum Density")
pylab.ylabel("Power (ms^2)/Hz")
pylab.xlabel("Frequency (Hz)")
def graphHisto(self):
pylab.hist(self.rris,bins=20,ec='none')
pylab.title("RRI Deviation Histogram")
pylab.ylabel("Frequency (count)")
pylab.xlabel("RRI (ms)")
#pdf, bins, patches = pylab.hist(self.rris,bins=100,alpha=0)
#pylab.plot(bins[1:],pdf,'g.')
#y=self.smooth(list(pdf[1:]),10)
#x=bins[10:len(y)+10]
#pylab.plot(x,y)
def saveBeats(self,fname):
print "writing to",fname
numpy.save(fname,[numpy.array(self.bx)])
print "COMPLETE"
def loadBeats(self,fname):
print "loading data from",fname
self.bx=numpy.load(fname)[0]
print "loadded",len(self.bx),"beats"
self.genRRIs(True)
def snd2txt(fname):
## SND TO TXT ##
a=ECG()
a.loadFile(fname)#,100000,4000)
a.invertYs()
pylab.figure(figsize=(7,4),dpi=100);pylab.grid(alpha=.2)
a.graphTrace()
a.findBeats()
a.graphBeats()
a.saveBeats(fname)
pylab.show()
def txt2graphs(fname):
## GRAPH TXT ##
a=ECG()
a.loadBeats(fname+'.npy')
a.removeOutliers()
pylab.figure(figsize=(7,4),dpi=100);pylab.grid(alpha=.2)
a.graphHRs();pylab.subplots_adjust(left=.1,bottom=.12,right=.96)
pylab.savefig("DIY_ECG_Heart_Rate_Over_Time.png");
pylab.figure(figsize=(7,4),dpi=100);pylab.grid(alpha=.2)
a.graphFFT();pylab.subplots_adjust(left=.13,bottom=.12,right=.96)
pylab.savefig("DIY_ECG_Power_Spectrum_Raw.png");
pylab.figure(figsize=(7,4),dpi=100);pylab.grid(alpha=.2)
a.graphFFT2();pylab.subplots_adjust(left=.13,bottom=.12,right=.96)
pylab.savefig("DIY_ECG_Power_Spectrum_Weighted.png");
pylab.figure(figsize=(7,4),dpi=100);pylab.grid(alpha=.2)
a.graphPoincare();pylab.subplots_adjust(left=.1,bottom=.12,right=.96)
pylab.savefig("DIY_ECG_Poincare_Plot.png");
pylab.figure(figsize=(7,4),dpi=100);pylab.grid(alpha=.2)
a.graphRRIs();pylab.subplots_adjust(left=.1,bottom=.12,right=.96)
pylab.savefig("DIY_ECG_RR_Beat_Interval.png");
pylab.figure(figsize=(7,4),dpi=100);pylab.grid(alpha=.2)
a.graphHisto();pylab.subplots_adjust(left=.1,bottom=.12,right=.96)
pylab.savefig("DIY_ECG_RR_Deviation_Histogram.png");
pylab.show();
fname='publish_05_10min.snd' #CHANGE THIS AS NEEDED
#raw_input("\npress ENTER to analyze %s..."%(fname))
snd2txt(fname)
#raw_input("\npress ENTER to graph %s.npy..."%(fname))
txt2graphs(fname)
NEW:
Salil notified me that he used a similar concept to create an ECG machine using some fancier circuitry to eliminate noise with hardware rather than rely on software. Way to go Salil! Here’s a video of his project: http://youtu.be/uV8UyEQxVII
This entry was posted on Friday, August 14th, 2009 at 9:15 pmand is filed under Circuitry, DIY ECG, General, Microcontrollers, Python. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.
64 Responses to “DIY ECG Machine On The Cheap”
| Filipe YaBa Polido wrote the following at 05:43:44 PM on August 22nd, 2009 |
|
Excelent! |
| Scott wrote the following at 05:53:13 PM on August 22nd, 2009 |
|
There’s an open EEG project which seeks to do just that. Check out http://openeeg.sourceforge.net/doc/ |
| wael wrote the following at 11:07:16 PM on August 22nd, 2009 |
|
verygood article i’ll try this project as soon as i can , just hopt it gives me more correct output than my all brevious projects . but as i can see here , the picture in this article doesnt show the ideal ECG pattern , P-QRS-T you know , whay is that ? another quis : how can i improve such a project to become a 12-leads ECG ? thanx for sharing |
| Scott wrote the following at 11:48:07 PM on August 22nd, 2009 |
|
The P wave is probably lacking due to imperfect placement of the leads. Moving the leads around your chest changes the shape of the trace. http://www.swharden.com/blog/images/filtering.png recorded on a different day shows the P-QRS-T waves nicely. As far as creating a 12-lead ECG, just repeat the process 12 times! The trouble is getting it into the PC. Sound cards only allow 2 channel inputs (right, left). Search the page for the word “microcontroller”. If you use a microcontroller to analyze the data, I’ll bet you can switch it rapidly between leads, recording voltages as you go, and dumping the data (voltage for each lead) directly to the PC in text format through the serial port. There are many ways you could do it, but that’s an easy one. |
| Scott wrote the following at 11:49:46 PM on August 22nd, 2009 |
|
Also remember that this is a single op-amp circuit, designed only to accurately assess R-to-R intervals, which it does well. For detailed visualization of the small features (such as the image I just linked to), build the 6-op-amp version. |
| Graeme wrote the following at 12:40:04 PM on August 23rd, 2009 |
|
I read somewhere that ECG signals are “chaotic”, in the sense that weather is, the butterfly effect and all that. Would be interesting to do that kind of analysis of your ECG data |
| Andrew wrote the following at 12:39:20 PM on August 24th, 2009 |
|
You don’t know of any way to do this same thing with an EEG do you? That would be amazing! |
| Leon wrote the following at 02:11:23 PM on August 24th, 2009 |
|
Exelent work! Arduino (www.arduino.cc) could be platform to go further. |
| Cameron wrote the following at 05:04:44 PM on August 24th, 2009 |
|
Please don’t do this without the opto isolator, it’s potentially lethal. You’re putting electrodes on your heart and providing a direct electrical connection to your pc (which is on mains power and could short). It’ll be the best $2 insurance policy you ever bought. |
| Scott wrote the following at 10:13:01 PM on August 24th, 2009 |
|
Andrew: Open EEG project for brain waves: http://openeeg.sourceforge.net/doc/ Leon: Yeah, but why waste a whole development board when a single $2 AVR could handle it? Check out my “microcontrollers” category. Cameron: agreed. But… again… how would that be different than plugging headphones in your computer? |
| charles wrote the following at 09:53:21 AM on August 25th, 2009 |
|
Awesome tool. Nice job. What program did you use to create the diagrams and the circuit? |
| Scott wrote the following at 08:52:03 PM on August 25th, 2009 |
|
Inkscape! http://www.inkscape.org/ |
| Occamboy wrote the following at 04:12:15 PM on August 26th, 2009 |
|
Ditto on the earlier isolation comment. The same conductive path that allows you to measure signals coming from the heart could just as easily conduct electricity *into* the heart. Less than a milliamp of current injected through the heart can cause cardiac arrest. This is not trivial stuff. ECGs need to be electrically isolated from the mains and hazards in very specific ways. If you don’t know how to do this, then I strongly urge you to not to experiment with this. |
| Liz wrote the following at 11:50:03 AM on August 28th, 2009 |
|
Wow… that’s amazingly cool. Thanks for sharing the idea and the plans with everyone! |
| eric wrote the following at 08:02:21 PM on September 27th, 2009 |
|
wtf?! THIS IS INCREDIBLE. i am building one right now!! might throw a PIC on it and let it use the usb data as well as power |
| Anonymous wrote the following at 07:53:08 PM on October 2nd, 2009 |
|
Wow. You’ve got a huge Q wave. You’ve had that looked at, right? |
| jim wrote the following at 12:11:02 AM on October 14th, 2009 |
|
Hi, excellent work on self-tracking. but do you know a cheap way (budge around 50-100) to make a eeg machine? An eeg is very useful in terms of introspection and mediation |
| Free Domain Analysis wrote the following at 08:02:29 AM on October 16th, 2009 |
|
My friend sent me this URL in an email, she said that I’d really enjoy your post. Peace! |
| Trackback – Free Internation Call >> How to make free international call wrote the following at 04:56:20 PM on November 19th, 2009 |
|
,[...] http://www.swharden.com is one nice source of information on this subject,[...] |
| Danny wrote the following at 09:33:01 PM on December 19th, 2009 |
|
Is there a schematic to make a safer home-made ECG with opto isolator as suggested? |
| Ganesh wrote the following at 05:23:09 AM on January 9th, 2010 |
|
Hi, its an excellent work. we are doing project on same topic,but we want to implement it on mobile phone so can you help us to achieve the same. Waiting for your reply….. |
| joyce wrote the following at 11:35:13 AM on February 21st, 2010 |
|
COULD I KNOW IF AN OPTOISOLATOR IS REQUIRED FOR THIS.IF SO.WHICH WOULD BE THE BEST TO BE IMPLEMENTED?I AM USING A 3 LEAD SYSTEM FOR MY CIRCUIT.ISNT OPTO ISOLATION A MUST… |
| RJ wrote the following at 10:14:25 PM on March 6th, 2010 |
|
ECG application example in an AD appnote: http://www.analog.com/static/imported-files/data_sheets/AD620.pdf Page 15. |
| eathan wrote the following at 04:52:03 PM on March 17th, 2010 |
|
Hey I just soldered most of the circuit together (the simple one). Though I’m not sure if/how it will work. I grabbed the only op amp that radioshack had. 741 op amp. I’m not sure if this is interchangeable with yours. Before I hook up to battery power, I wonder if you could explain? Also, is it possible to use a 9v batter instead. Why or why not? and how would i go about grabbing usb power? Obviosly I’m a little green with electronics. Thanks so much. this project is very cool and I’m glad you shared it. E |
| Jdog wrote the following at 08:30:35 AM on March 30th, 2010 |
|
i think this idea you have is inspirational no a better way to describe it would be genious and the idea for using the voice recorder is good also that could work as well you should try it it is the same principle as the holter monitor used by cardiologist to diagnose arrhythmias in the home setting try it and remember keep moving forward |
| william rufus wrote the following at 06:02:44 AM on May 28th, 2010 |
|
Dear sir, This is to inform you that i am interested in buying these medical products from your company,viz, (1) EKG MACHINE (2) PATIENT MONITOR (3) DEFIBRILLATOR MACHINE I will like to have their price and to know their availability in stock so as to Your quick response will be highly appreciated. Thanks |
| Scott wrote the following at 07:20:53 PM on May 28th, 2010 |
|
I can get you an EKG machine for $200, a patient monitor for $150, and a defibrillator machine for $300. All of these devices will be made from parts reclaimed from old TVs, Styrofoam, and likely some popsicle sticks. |
| Filipe wrote the following at 03:32:17 PM on May 29th, 2010 |
|
Hi I love this project and I try make it but this not work I try make the 1º circuit example with lm358 but I only see pulse on osciloscope when I conect to the leds and signal generator… to make the leads I have gym bike heart beat contacts (I think it is better) you have an idea to help me? if you can, add me on msn filjoa@hotmail.com I like very much make an project like that. best regards, |
| hesham wrote the following at 07:35:35 AM on June 23rd, 2010 |
|
hi i am a student at the last year at the faculty of engineering- Assiut University-Egypt |
| hesham wrote the following at 07:43:03 AM on June 23rd, 2010 |
|
Dear sir i forgot to tell you that i made the circuit and it works properly now but needs a good notch filter please help me to do it on python |
| vivek wrote the following at 12:41:12 PM on June 23rd, 2010 |
|
good work dude….but the soundcard n goldwave dont pick up things under 20 Hz (or do they??)….n most f useful ecg signal is under 20 hz….so how does it work |
| hesham wrote the following at 08:06:54 AM on June 26th, 2010 |
|
so what is the solution ? thx for yr attention. |
| hesham wrote the following at 04:33:08 AM on June 28th, 2010 |
|
dear sir i have some problems using python one of them it stops working during excuting and a run time error appaers and the figures doesnit appear please help me …… |
| hesham wrote the following at 04:34:29 AM on June 28th, 2010 |
|
waiting for your replay |
| Biolyons wrote the following at 01:33:33 PM on September 15th, 2010 |
|
Very concerned looking at things like this – as a senior Clinical Engineer I can tell you of a condition known as microshock where currents of just 40mA can do damage to your heart – DONT build something like this without complete electrical isolation of the patient leads – a quality optoisolator on each patient lead is a minimum. FYI commercial units have to be able to withstand 500v being placed on the back end without breaking through to the leads. |
| ian roberts wrote the following at 05:03:57 AM on September 16th, 2010 |
|
Sir I am an electrical dunce with a heart arrythmia problem and a pacemaker inserted for syncope (low blood pressure) attacks. I live in Indonesia with relatively poor medical resources locally. I am absolutely in awe of your capability and of course would love to build this device for home monitoring and recording but truly I find it too daunting. I may task a local smart kid to try it. Thanks so much for a fascinating article. Well done. |
| Muni Sakya wrote the following at 09:06:38 AM on September 19th, 2010 |
|
We are a team of doctors and engineers join hands together to serve the under privileged and underserved people of the remote rural part of our country called NEPAL. So far we have examined 120 patients of different diseases and your article and somple ECG schematics can serve our general need towards the state of the hearts of the cardio patients. WE love to build one and use asap. |
| Anonymous wrote the following at 01:37:08 PM on September 26th, 2010 |
|
Excellent article… Really exciting. Hope to try it soon. |
| Bobby wrote the following at 03:43:15 PM on September 27th, 2010 |
|
I’ve tried building this but it won’t work; I did however act as an antennae as mentioned in your youtube video. I had the capacitor connected at the time but maybe incorrectly , which is entirely possible since I’m not too familiar with schematics and implementing them. Thanks for the wonderful article tho. |
| Bobby wrote the following at 08:01:31 PM on September 29th, 2010 |
|
I just noticed too, that the station I heard was spanish. The guy was advertising their station, 105.something. I live in Orange County, California. Did we hear the same station? O_o??? |
| linliehhann wrote the following at 11:58:21 PM on November 23rd, 2010 |
|
I just build fancy lm324 version and used oscilloscope softare and free ekg software, it just come out as commercial ecg, just try to use right leg device to reduce interference I am looking for 12 lead ecg for poor country,amazing guide! |
| rahimie wrote the following at 11:34:54 PM on December 1st, 2010 |
|
Hi, i would like to know how to set up live mode in the goldwave software? |
| Dider wrote the following at 02:06:04 PM on December 16th, 2010 |
|
Hi, I tried the simple version with just 1 op-amp but i get nothing, really noting. Does somebody got this schematic working? Thanx in advance |
| Anonymous wrote the following at 10:52:45 AM on February 16th, 2011 |
|
hahahahahahahahahahahaha heheheheheheheh |
| Anonymous wrote the following at 10:58:57 AM on February 16th, 2011 |
|
wat are yu lol about hehehehehehehehehehehe >:( :lol |
| sensor headset wrote the following at 04:48:07 AM on April 20th, 2011 |
|
. The George Greenstein Institute approached me to create a class. The first thing I wanted to do was finally explore the EEG machine. The idea of using quantifiable information, gleaned from the brain itself, representing it in a variety of manners — from purely aesthetic to powerful data visualization — got my mind humming with possibilities. Directly interfacing with the individual experience of perception is a terrain I had not yet been able to directly explore. Through open source hardware I was finally in a position to begin experimenting with how my own mind responds to stimuli. In addition, the format of taking the research directly to a classroom for further development amongst a background of many interests offered new possibilities for refining the technology. . This is my first comment. Your blog has been very useful for me and it provides very good content and too informative,. |
| Enric G. Torrents wrote the following at 05:14:34 AM on April 22nd, 2011 |
|
Dear all, as new honorary consul of the hispanoasiatic chamber of commerce Hispasia I am promoting the implementation of open science devices in university and schools labs, specially in those of deprived areas unable to afford regular, commercial ones. I am looking for an EEGs designs ready for distribution either as a pre-made kit or a DIY one, reliable and precise enough to be both a learning and a research tool. Please get in touch with me with feedback on the proposal and ideas on other open-science devices I could propose to the institutions. Many thanks for your attention, Enric G. Torrents – |
| mostafa wrote the following at 01:01:23 AM on June 7th, 2011 |
|
its wenderfull i am from iraq but i living in uae dubai i like your machine thanks and look forword to you |
| Gabriel wrote the following at 12:15:52 PM on June 12th, 2011 |
|
Hi, your blog is really great and i loved the projects posted. I’m trying to build an ECG analog circuit to print the waves on the pc screen as you did, but using a microcontroller. At first, I ll use an Arduino board to develop an then update it just for an avr microcontroller. I wanna WARNING you guys, that we need galvanic isolation for the patient, otherwise a small current (such as mA) can provide a microshock (as mentioned above). Answering your question, the headphone is different because there isn’t a directly electrical connection to your body. In this case, the current goes to speakers that moves mechanical waves trough the air (sound) to your ear. You can provide a safer circuit using optoisolators between the signal that will goes to pc and the pc (or making it wireless). The Op Amp is characterized by having a large input impedance, and, with a 9V top, the current that could go to patient is insignificant (uA or less). If you try to use a right leg drive (RLD) just put a resistor (at least 1M) between the output of the amplifier and the patient. Also use the diodes to prevent any large tension on the leads. As soon as I get something to publish, you will hear about here. Thanks for the ideas. |
| Uttam Dutta wrote the following at 03:40:18 AM on June 29th, 2011 |
|
If I make lm324 fancy version with potable LCD oscilloscope how will be tthe dispaly, (I do not use any software) , can any body answer |
| phillip wrote the following at 04:23:59 AM on July 13th, 2011 |
|
Great stuff mate. I hope you are on our side. One thing though, I think a second is 1/6min which is 1/60 hour= 1/24 day= 1 earth rotation etc etc or something like that. cheers |
| darren wrote the following at 03:29:28 PM on July 29th, 2011 |
|
Hi, I tried to make this amplifier circuit but the scematic is very hard to follow. Also it doesnt tell you how to wire the stereo socket (least i dont think so) – the socket has 3 pins but there are only 2 outputs? Anyone think they could draw a digram of this on a breadboard so i can see exactlly how to wire it. I really want an ecg machine lol Thank you Timez |
| darren wrote the following at 04:25:35 PM on July 29th, 2011 |
|
Im not even getting the heatbeat on the live test that you do before you record |
| Darren wrote the following at 10:32:58 AM on July 31st, 2011 |
|
I do get lots of noise when i touch the + lead tho – but as i say cant pick up the heatbeat signal at all? – anyone? (maybe its cos im making the wires that attach to the electrodes too long – i cant find sheilded wire anywhere – only audio cable – i cant use that for electrode leads tho right? because they have 3 wires inside? Please someone help – or im gonna have to give up on this one because it wont work for me. |
| Lydia Eule wrote the following at 10:36:42 AM on August 1st, 2011 |
|
dear sir, |
| Frank Abbing wrote the following at 07:53:58 AM on September 26th, 2011 |
|
Dear mr. Harden, I built the Nguyen version of the circuit. After some checking and double checking it works very well. I found the free oscilloscope by mr. Zeitnitz very useful when troubleshooting. Frank |
| beats headphones wrote the following at 04:20:33 AM on October 13th, 2011 |
|
Monster Beats by dre headphones produces an individual intense level of comfort. This kind of class of monster beats goods, which includes monster music by dr dre studio room, are constructed of poor substance that produce a hearing sense probably considering the none of the major depression due to headsets. Thus if you can be sporting monster beats by just dr dre studio headphones, you’re feeling the selected music, not just the individual headsets. And monster beats as a result of dr dre studio using ultra-soft breathable components retains a large reputation, both in the lifetime of workshops and among shoppers. |
| Blair wrote the following at 04:33:37 PM on November 21st, 2011 |
|
It is usually difficult to get skillful individuals on this topic, nevertheless, you sound like you are aware of exactly what you are preaching about! Many thanks |
| Maris wrote the following at 06:51:41 PM on December 2nd, 2011 |
|
Hi there I discovered your webpage by mistake when i was searching Yahoo for this subject, I need to say your page is absolutely valuable I also love the layout, it is wonderful! |
| free one month xbox live codes| free xbox live codes | free xbox accounts | free xbox codes | xbox accounts wrote the following at 01:17:53 AM on December 24th, 2011 |
|
I?ve read several excellent stuff here. Definitely worth bookmarking for revisiting. I wonder how a lot attempt you set to create any such wonderful informative website. |
| Mike wrote the following at 06:51:25 PM on January 6th, 2012 |
|
Cool post, thanks. I am currently working professionally on a Defibrillator Tester and did some research into ECG for the project. That, and occasional weird beats (PVC?) I notice have piqued my interest in self-monitoring. I have a pretty decent USB Audio Mixer I have previously used to record ECG – hand to hand, but not in acceptable quality. After reading your post I think I should try the pennies; maybe it can give a better SNR. |
| Antonia wrote the following at 07:49:35 AM on January 22nd, 2012 |
|
Great addict of this blog, a considerable number of your articles or blog posts have definitely helped me out. Looking forward to up-dates! |
| Ozella wrote the following at 01:33:09 PM on January 22nd, 2012 |
|
This is exactly a little something I must do more research into, i appreciate you for the posting. |
| Héctor wrote the following at 03:26:06 PM on February 3rd, 2012 |
|
Hi I am glad to see this awesome project is very interesting, i will do it for a project of my school, if i can make it i will share my results, but i have a doubt about how did you do the communication between the circuit and the PC using the sound card, there is some help you can give me about that or any webpage where i could see it well thanks for the project and i send you grettings from Mexico |
