Fate Posted February 25, 2005 Report Share Posted February 25, 2005 Hey... I'm working on a heartbeat detector & monitor (using photodiode & detector not microcontroller) for my mini project and need help in designin it... Any kind of help will be greatly appreciated...Thanx Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 26, 2005 Report Share Posted February 26, 2005 Hi Fate,Welcome to our forum.I found this on the 1st page of a search for Heartbeat on Google:http://www.web-ee.com/Schematics/HeMon/HeMon.htm Quote Link to comment Share on other sites More sharing options...
Fate Posted February 26, 2005 Author Report Share Posted February 26, 2005 Hey... Thanx for the help but I already got my hands on that one... :P But I've to work without microcontrollers and Pic... :-\ Don't know... Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 26, 2005 Report Share Posted February 26, 2005 Hi Fate,You wanted a heartbeat detector so there it is. The detector part I posted has a dual opamp but not a microcontroller nor Pic.Now what do you want to do with it? Quote Link to comment Share on other sites More sharing options...
Fate Posted February 26, 2005 Author Report Share Posted February 26, 2005 :-[Hmmm... Now I want to amplify it (a lot)... feed the output to a comparator and then to a mono to get like proper pulses and then count them (per min)... Any more suggestions... ??? Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 27, 2005 Report Share Posted February 27, 2005 :-[Hmmm... Now I want to amplify it (a lot).Hi Fate,Look at "B" opamp, no negative feedback. At the low frequency of heartbeats, its gain must be 100,000 or more. You won't have to amplify it.... feed the output to a comparatorLook again at "B" opamp. It is a comparator, and it even has an adjustable threshold!It probably already has "proper pulses" so just feed them to a counter.This circuit is self-contained and has everything that you need. That's why I selected it for you. ;D Quote Link to comment Share on other sites More sharing options...
Fate Posted February 27, 2005 Author Report Share Posted February 27, 2005 Muah!!! :D Quote Link to comment Share on other sites More sharing options...
Guest Posted February 28, 2005 Report Share Posted February 28, 2005 how to code the oscillator display? Quote Link to comment Share on other sites More sharing options...
Fate Posted February 28, 2005 Author Report Share Posted February 28, 2005 Are you working on the same thing?DesignGuide.zip Quote Link to comment Share on other sites More sharing options...
Guest Posted March 1, 2005 Report Share Posted March 1, 2005 yah.. but i wanna noe the lm358 op amp output type.. can u explain how it operate? wats the use of sensitivity and trigger level? thanx a lot Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 1, 2005 Report Share Posted March 1, 2005 Hi Bird,The output type of an LM358 opamp is a complementary push-pull emitter-follower stage like most other opamps. See its schematic attached. The LM358 and its big sister, the LM324 quad opamp, is unique in that it can operate with a single supply voltage as low as 3V, and has a very low idle current. In this circuit it operates at 5V.Opamp A operates as an ordinary AC non-inverting amplifier, with its gain adjusted by the sensitivity pot.Opamp B operates as a comparator, with an adjustable trigger level.I guess the sensitivity and trigger level pots allow the circuit to match the enormous difference between different fingers. Probably when a finger is cold, it has low blood-flow.For its display, you need a counter circuit with a timebase measuring pulses per minute. Quote Link to comment Share on other sites More sharing options...
trigger Posted March 1, 2005 Report Share Posted March 1, 2005 I still can't figure out how an LED and LDR can measure the heartbeat................. by what theory it is based on?? Anyone can explain this? ??? ??? Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 1, 2005 Report Share Posted March 1, 2005 Hi Trigger,I guess the blood flows in a finger in pulses with each heartbeat.The blood either blocks or passes the red light from the LED with each heartbeat.[move]Whoa! 2000 posts![/move] Quote Link to comment Share on other sites More sharing options...
Guest Posted March 1, 2005 Report Share Posted March 1, 2005 i onli can manage to get lm358am chip.. is it ok? Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 1, 2005 Report Share Posted March 1, 2005 Hi Bird,You didn't look it up on Google, did you?National Semiconductor's sales information sheet says that the AM suffix is for a tiny surface-mount package. You probably want a DIL package for through holes mounting with a suffix of N. Quote Link to comment Share on other sites More sharing options...
Fate Posted March 1, 2005 Author Report Share Posted March 1, 2005 Hey Trigger... The optical technique presented here exploits the fact that tiny subcutaneous blood vessels (capillaries) in any patch of skin (fingertip, ear lobe, etc.) furnished with a good blood supply, alternately expand and contract in time with the heartbeat. An ordinary infrared LED/phototransistor pair can sense this rhythmic change as small but detectable variations in skin contrast. That's pretty much the gist of the theory it's based on... Quote Link to comment Share on other sites More sharing options...
Fate Posted March 1, 2005 Author Report Share Posted March 1, 2005 Hey Bird... Check out the data sheets for LM 358... Btw can't I like use two 741's instead? The specs are pretty much the same... LM358.pdf Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 1, 2005 Report Share Posted March 1, 2005 Hi Fate,A 741 opamp won't work with only a 5V supply, and its output won't go anywhere near ground for a proper logic low. The LM358, MC3358, MC3458, MC33072 or MC34072 will work much better, and they are all duals to match the pinout in the article. Quote Link to comment Share on other sites More sharing options...
Fate Posted March 2, 2005 Author Report Share Posted March 2, 2005 Hey Guru... Didn't quite get your point abt the output not going to zero... ??? BTW could u explain the PIC part of the circuit.. I'm totally new to the subject... Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 2, 2005 Report Share Posted March 2, 2005 Hi Fate,TTL counter ICs require the voltage from a logic low source to be 0.8V or less. The output of a 741 opamp won't go that low, probably 1.0V or more. The other opamps have outputs that go down to within millivolts from ground.I lost the whole article but the PIC was probably used as a pulse counter with a 1 minute timebase. Quote Link to comment Share on other sites More sharing options...
Fate Posted March 3, 2005 Author Report Share Posted March 3, 2005 PIC?? ??? Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 3, 2005 Report Share Posted March 3, 2005 Hi Fate,A PIC is a microcontroller that you must program like a computer to do counting and display multiplexing. You could use many separate oscillator, counter and gate ICs instead. Quote Link to comment Share on other sites More sharing options...
Guest Posted March 4, 2005 Report Share Posted March 4, 2005 hi all,were should i get the light screen?? and were to put d finger? Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 4, 2005 Report Share Posted March 4, 2005 Hi Bird,Go and see one at a drugstore (chemist?). Quote Link to comment Share on other sites More sharing options...
Guest Posted March 4, 2005 Report Share Posted March 4, 2005 drugstore?? dun understand... i constructed d circuit..anyway i cant get wat it suppose to be.. i test d heartbeat using oscilloscope.. i oso dunno how many value should i put on both potentiometer Quote Link to comment Share on other sites More sharing options...
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