Heart beat sensor

These op-amp filters are great... I used one similar to this a year or two back and connected it to an arduino. I bought an IR transmitter/detector matching pair to drive it from my finger, but in practice I found that a simple white LED as transmitter and tiny cheap LDR worked much better than the IR pair. The result was amazing ... the  arduino software scope showed excellent pulses. Two op-amps worked, but I added the third op-amp for amplification and the result was clear and large. The fourth part of the quad op-amp (which in all is only the size of a 555) was never needed. A little Arduino programming ... and a readout of pulse per min was right there.... it could even show a clear pulse from anywhere on my arm/face/neck etc... brilliant.

Very nice

@sithin, Problem with this topology is its single ended way. To measure human body voltages you need a differential way to amplify. Single ended it get to much interferences amplified and not the signal you want to. Keep it up!

@2ctiby, 555 it an 8pin package, while 4 opamps do need at least 4x3=12 for the amps, and 2 additional pins for supply which makes 14pins.

@Hurz... The point which I casually mentioned there is that the size and shape of a quad amp (4 x op-amps built in together) is very similar to to the size and shape of a 555. When I first started reading schematics I somehow thought that 4 op-amps would take up quite a lot of room. I was pleasantly surprised when I found that all four were within a small component which is hardly larger than one 555.

@Hurz... The heart beat monitor which we are discussing here is not about detecting body electricity. Here it is detecting the change in skin colour (change in frequency of 'colour') ... Every cell in our body, including every cell of our living skin, needs oxygen to stay alive. The heart pumps this oxygen via the blood to every single living cell (including the skin cells) with every beat. Each time that happens, there is a change in colour momentarily of every cell due to the oxygen content while it lasts (soon to need replenishing by the next beat). Our eyes do not notice the very subtle change in colour frequency (although blushing and exercise make it noticeable with red skin). This setup is well capable of causing a tiny blip on a scope which can easily be amplified.... and that it why this method works so well. An oximeter is a more elaborate method of this, whereby the change of colour (oxygenated/deoxygenated) is more intricately measured (infra-red vs other frequency colour), and is used to give an estimation of the oxygen content in each beat ...we often see these little detectors placed on the finger in hospital patients... but for our purpose here we are simply detecting the basic change... and a simple red/white LED (as transmitter) next to a LDR (as receiver), works amazingly well ... not to be confused with an ECG (EKG) electrical setup.

@Hurz ... The op-amp setup acts as a frequency filter for zero to approx 3 or 4 Hz if designed correctly, so the heart blips are easily distinguished from scraping material (light from fibre variations) etc. Placing the LED right next to the LDR with just a tiny piece of dark plastic/card between is all that is needed. Put the two together at the end of a makeshift tube, then hold that tube end on the skin (best not to press it I found)... I used various tubes (ie cylinders) ... my best one was a hand laser with its innerds removed, although other tubes were rather similar, such as a mini torch likewise with its innards removed.

About that quad op amp size... Many years ago I went to a shop with a guitar enthusiast friend to try out some amps etc. We enquired to the young slim girl assistant asking if she had an amp which we could try. Yes, she said...I will fetch it from the back room. I asked her if we could help lifting it out. No, It's ok she replied.... She came back a few minutes later with the amp..... about the size of a mobile phone ...lol.

@2ctiby, the author of this circuit does not mention the use of light sources, or detection of light. Even so, i would suggest that a phototransistor might be more sensitive than ye old LDR ?

Which shop was that? Where? QTH?

Cowley road Oxford?

What other stuff did she keep in the back room?

Don't you mean band pass filter not 'frequency filter' which actually has little meaning?

Your doctoral thesis which starts "The heart beat monitor which..." Contains thee word whereby, which notwithstanding the aforementioned, i specifically detest!

I suggest, rewriting of said doctoral thesis, effective immediately. Additionally, one should spend more time at the Radcliffe science library, preferred position is in the basement. You may now order your books online! These will be placed upon your bookshelf ready for reading by 9:00 AM sharp!

@zorgrian... Author did not mention...blah, blah, but I gave my usage of this type of setup here. Phototransistor, photodiode, LDR...whatever .... the LDR works just fine. Shop name and town from many years back wanted....strange. A passing enquiry in this second hand shop for an amp, on our way to the music shops...not an unusual venture....back room stock ... don't know...never went in there. Yes band pass as OP described, or low pass as I insinuated. Doctoral thesis?...hang up of some sort with you? Don't you just hate the word 'detest'?

Nay, good sir, for what good reason would I give emotive energy to a harmless word such as.... Detest!

"On our way" eh? Who or whom might it be that purportedly, did accompany a said 2citiby, evidently of advancing years, to said music shop (the whereabouts of which are undisclosed)?????

Seems to me zorgrian, that we perhaps need to step aside from electronics for a moment .. http://everycircuit.com/circuit/5124226792292352

@2ctiby, I dont read all your followup comments with @zorgrian and you, however I agree with zorgrian and the author doesn't mentioned anything about photoeffects and detector or transmitters. This is all in your fantasy. BTW, the author already said lower corner is 0.5Hz and upper is 3.4Hz! Colour change is used for oxymeters, right but why so complicated for pulsmeters? That is over-engineered in your fantasy, the pulse can be detected by just modulating the amplitude of the transmitter signal, by more or less blood to every single cell of your body and this will also work as a reflex light sensor. But measuring a colour change is definitive not needed. Its needed for oxymeters and there is a quite tricky technic behind.

@hurz ... We are not in conflict here, we are really saying the same thing. You mentioned 'the amplitude of the transmitter signal'. ... Yes,... it is the blood 'colour' at the skin which creates that amplitude change for a short duration each second, ie a change of light intensity from the LED baseline and so creates a frequency of about 1 or 2 Hz seen on the scope ...that was the colour and frequency to which I was referring, the point being that it is not the electricity of the body or sound pressure... I did also describe that an oximeter was a more elaborate piece of equipment using IR (I have one of these incidentally).

Again, if its done with light then its NOT any colour which will be detected, its then the brigtness which is modulated like AM. Colour demodulation is used for oximeters and much more complex. But here my very first guess is, the information is current and voltage which is taken from patient body by electrods. Everything else is to much speculation.

Thank you for all comments...Actually its a base design and need much more corrections in realtime applications. We can use a photo detectors as sensors for detecting the color changes in the tip of a finger. During systolic the blood volume at the finger tip is high and darker..This color gradient is the key sensing input...so need to choose a best approach for extracting the input signal.

Comments are invited for my next ckt. Please suggest on this design. http://everycircuit.com/circuit/5732400054665216

No comment!

@sithin, if the information is as flat in this new project as it is here, no thanx I dont follow. Anyway, you start a new project before the old one is finished? I think you are more on your own from now on. Be an active part in discussion next time from begining might help to keep the reader at your circuits.