Heart rate counter without microcontroller - Page 1
Forum section: electronics / beginners

author: MrOmnos
author_rank: Frequent Contributor
timestamp: May 15, 2016, 03:05:05 pm
content: Hi, I have made heart rate monitors before. I used Arduino, IR sensors and emitter and a amplifier to display a heartrate from the finger tips of a person on a seven segment diplay. Is there anyway to implement is without using a micro controller? I know how to do the sensing (using IR sensor) and signal conditioning. I want to display the heartrate on 2x 7 segment display.

author: jeroen79
author_rank: Frequent Contributor
timestamp: May 15, 2016, 03:50:24 pm
content: You can build one from individual TTL or CMOS chips.Just a few stages of decade counters that count the heart beats.Then every minute you put the output in a buffer for the display and reset the counters.Why do you want to do it without a microcontroller?

author: MrOmnos
author_rank: Frequent Contributor
timestamp: May 15, 2016, 04:37:38 pm
content: Quote from: jeroen79 on May 15, 2016, 03:50:24 pmSeems like too much trouble. If I were make something like a " led VU meter" you have in audio equipment so that with every heart beat a set of Leds would light up from down to up. How would I implement that without using a micro-controller.Something like this but simpler

author: aurmer
author_rank: Regular Contributor
timestamp: May 15, 2016, 04:46:28 pm
content: Here is my crack at it. I don't know many advanced circuit designs, but a rudimentary design might look like this.Sensor>Array of bandpass filters (your monitor's accuracy will depend on the filter count and resolution)>Each bandpass output feeds to a smoothing filter to get a measurable amplitude (voltage) for each freq range>Logic circuit which compares the filter outputs (voltage) and identifies the strongest voltage (aka the freq range which the heart rate falls into).>Output of logic circuit is a quantized voltage specific to the heart rate measured. An ADC will "decode" this output voltage giving you the bits you need to drive the display.>The ADC output is run through gate logic to convert to display segment bits.This avoids programmable controller chips, but after thinking it through, it seems a bit convoluted, no?Unless this is just a thought experiment in "how could it be done without a ?C", I would say this is exactly why microcontrollers were created, and excluding it from design is like building a skyscraper without steel.

author: rstofer
author_rank: Super Contributor
timestamp: May 15, 2016, 04:50:18 pm
content: That's easy! Easier with a microcontroller but easy nevertheless.You just build a tachometer circuit but with much longer time constants. Every time you get a pulse, you dump some charge in a capacitor. Usually this is done with a one-shot firing at every pulse so that the added charge for each pulse is constant. The charge drains off the capacitor at some rate determined by a resistor. In the end, a faster heart rate adds more charge than the resistor drains and the capacitor voltage increases. The rest is just details. Analog bargraphs should be pretty easy to find.And, no, I wouldn't do it this way. But, in theory, it should work.

author: mav_iqdirect
author_rank: Contributor
timestamp: May 17, 2016, 11:39:26 am
content: You may build some kind of opamp integrator plus VU-meter if you like. Adjust the integration constant and you'r done!

author: alanb
author_rank: Frequent Contributor
timestamp: May 18, 2016, 01:13:30 pm
content: Quote from: MrOmnos on May 15, 2016, 03:05:05 pmWhat is the downside of using a micro controller that you are trying to avoid?Micro controllers are not just Arduino's. Arduinos include functionality that you may not need and a physical size that may be greater that you desire. You could use a Microcontroller such as a Pic or Atmel without the additional support circuitry that is included in the Arduino.

author: Seekonk
author_rank: Super Contributor
timestamp: May 18, 2016, 08:01:17 pm
content: Considering I have a few tubes sticking out of me right now, I am interested in building one. Interesting that half the monitors here won't read 150 or more beats per minute. Need something to check me at camp. Honestly I can't feel the difference.

author: Raj
author_rank: Frequent Contributor
timestamp: May 22, 2016, 03:33:18 pm
content: Quote from: MrOmnos on May 15, 2016, 03:05:05 pmhow about using multimeter's frequency count function paired up with logic circuitry that feeds your heart rate to it?you could also use ir led and photo diodeconnect ir led to battery and photo diode to long scantime oscilloscopemake the ir led and photo diode face each other with your finger interrupting them