Comments for "Homebrew Photoplethysmography"

28th February 2012 21:24

silicon mix wrote ...

nice photo thingy video.

may i suggest you cut down on the salt a little :)

3rd April 2010 17:23

Riaan wrote ...

Sheesh guys, do you really need to be spoon-fed like this - Alan will post the circuit if he is happy with it. Try doing it yourself while you are at it waiting. You might just learn something! go to or and type in photoplethysmography. You'll learn a great deal of electronics and biology.

18th January 2010 02:32

Phuong wrote ...


I am phuong.

I am doing the small project like yours but it's not work. I think my schematic have some problems. Please could you send me your schematic of Photoplethysmography ?


21st November 2009 11:45

Scooter wrote ...

I have a school project in need of a cheap heart rate monitor, is the schematic diagram available yet.

21st October 2009 09:50

Alan Yates wrote...


The LED is a plain red 10,000 mCd unit from the junkbox biased at about 20 mA. The detector is a phototransistor of unknown vintage from the junkbox, IIRC I purchased it from Tandy Electronics when I was about 15! I have no idea of its properties, it isn't marked, but physically it is clear-epoxy encapsulated with a large die on a black substrate into which the three gold-plated fairly short legs are terminated.

The LED and detector lie directly opposite each other with the finger in the transmission space. I tried back/side-scatter geometries but it didn't seem to work as well as direct transmission.

My lash-up is a terrible hack, that it works at all surprises me. A CdS photocell also worked, but the phototransistor was easier to work with.



26th September 2009 02:33

parisa wrote ...


I have a project for recording PPG and GSR at the same time,PPG circuit has gain about 100 and low pass filter with cut-off frequebcy about 40HZ,I use an IR-LED with a photo detector as a sensor for PPG,in the end I have nothing but noise,would you explain a little bit about your sensor and what was the angle between LED and detector?

23rd July 2009 04:52

Len wrote ...

Alan, I understand your perfectionist nature, but it would actually be more interesting if you could post a schematic "as-is" for others to see how your way-less-than-perfect circuit could perform so well. It's up to you of course, but people are asking, you why don't you just show your circuit's guts? Cheers

16th July 2009 10:05

Alan Yates wrote...


You never actually "needed" me in the first place, the textual description is more than adequate if you are prepared to do a little work for yourself. As far as being selfish, well I share my toys with the world for nothing and all you want is to be spoon-fed. Have some damn patience and common courtesy. Funny how 'net anonymity turns people into whiny demanding children.

I will eventually post the schematic, but as indicated in the article it is far from a usable solution. Any simple manually adjusted threshold technique will not be sufficient for general use.

Circuit linked is quite similar but has even less filtering and uses an LDR rather than a phototransistor. It will probably suffer from the same limitations. The 8051 based display is fairly conventional.



16th July 2009 06:23

SS wrote...

Hey mikeB brother, here I found a circuit that we want. We dont need him any more.I will be happy if I help you with this.Take it easy.


8th July 2009 00:17

SS wrote ...

selfish curmudgeon. Any no word!

16th June 2009 01:47

MikeB wrote ...

Hi Alan,

I have been looking for a circuit like this for a while. Tried building a couple but non seemed to work as well as yours in the demonstration.

I am currently working on a project where i need to find the pulse. Its for personal use, as a hobby.

I was wondering if you could provide a schematics for this. Or atleast a closeup picture of the circuit you build and component values. I would greatly appreciate it.

Thank you very much in advance.


6th June 2009 06:48

SS wrote ...

Sir, excuse me but I am an amateur and my english is not good.So if it is possible,Could you post the shematic to me? I promise , will use it only for personal use.Thanks.

12th May 2009 10:35

Alan Yates wrote...


The op-amp is an LM358.

The circuit I'll draw up later when I play around with it again. But basically it is as described; the amplifier is an inverting topology with a capacitor in the feedback loop to roll-off its HF response, the optical signal is recovered across the photo-transistor and capacitively coupled to the amplifier to give it some high-pass. The comparator very conventional. The exact values aren't too critical.

I've recently been given a commercial pulse-oximeter head to study by a very kind reader. So I will be revisiting this project in the near future.



8th May 2009 07:25

SS wrote ...

circuit and chip ?

26th April 2009 18:04

Alan Yates wrote...


Started a new job mate, so I've been kinda busy settling in.

However this weekend I've been into it again, I built an ionisation chamber radiation detector and *finally* got around to building a power supply for an Geiger tube I've had in the junkbox for years.

Right now I am accumulating data on the background radiation in the shack. I'll post the initial information shortly. Nothing special, uses Charles Wenzel's inverter design, but I integrated it to a Atmel Tiny13 to count the events and send them over RS-232 to the PC so I can graph the data.



25th April 2009 03:03

Arv K7HKL wrote...

Gee Alan, it has been almost a month since this latest VK2ZAY project posting. I hope my April Fools Day comments about the Mobius Strip Dummy Load has not gotten you all tied up in knots and unable to do further technical experiments?


29th March 2009 18:26

Alan Yates wrote...


The filtering needs much more work before it will be robust, so I wasn't going to write up the circuit diagram until I had finalised the filter.

The DC bias is just blocked by a 10 uF low-leakage electrolytic capacitor, nothing special there. The DC block cap along with the amplifier input resistance defines the high-pass characteristic. Low-pass is currently a single-pole implemented with a 56 nF cap across the feedback resistor.

I may switch to a photodiode and a transimpedance pre-amp before the band-limiting filter/amplifier stages. The phototransistor is very sensitive though and works quite well to detect the light modulation, but can saturate easily because of its sensitivity where the photodiode might have a bit more dynamic range. A back-scatter probe would be easier to build and perhaps less likely to saturate with different fingers/earlobes, but so far it doesn't appear to pick of as good as signal as transmission right though a finger. More work required with the probe end of things...

I'll post the full circuit once I have it working nicely.



29th March 2009 17:07

Hiran wrote ...


It would be nice if you could give a circuit diagram of the filter you used.Please also explain how you were able to remove the dc bias from the output signal so that you could amplify it without losing the signal.

Please reply.

Thank you.

Leave a comment on this article.