Suggestion Regarding Wearable Fitness Device (HRM and Temperature)

Hi all.

I have a project which is a Microcontroller based Wearable Device for Body Hearth Rate and Temperature Monitor. After reading the data need to be transfer to an App over Bluetooth LE.

Now I am looking for suitable Sensors. I found for HRM the below:

**broken link removed**

Will it be a good choose to use SFH 7050?

Also anyone have any suggestion on Temperature sensor which is suitable for Fitness Device to measure Body Temperature?

Thanks in advance.

Regards.

For HR monitor there are only really two choices, ECG electrodes or a plethismograph.

Each has advantages and disadvantages.
Personally I prefer an ECG belt around my chest, its not too uncomfortable and is not in the way.
I find something clipped to either my finger or my ear and attached to an electric cord rather uncomfortable and inconvenient during exercise.
Either the damned thing keeps falling off, or they clip on so tight they begin to hurt after a while.
Fine for a patient in bed, but not during frantic exercise.

Body temperature is pretty easy, just a thermistor, but it needs to be strategically located to be in good thermal contact with body mass. just taping it onto any exposed skin surface is not going to work terribly well.

Hi Warpspeed.

Thanks much for your detail reply.

I need plethismograph for HRM. As the device will be a wrist bad based and no option for chest belt.

Some more ques please:

- The SFH 7050 is Photodiode Output based. There are some other Biomon sensor which are I2C based. Which one you feel will be better to use Photodiode/I2C? To be personally feel Photodiode will be easy as I need to read the voltage only.

- For SFH 7050 with Microcontroller connection can you please advise on Schematic? Do I need to just drive the SFH 7050 LED's from MCU GPIO Pin can connect the Photodiode Anode to MCU ADC Pin and Photodiode Cathode to GND?

Thanks again.

Regards.

Not sure what I2C is, never heard the term before.

But the plethismographs I have seen all use a reflective optical sensor which bounces light off the surface of the skin. Skin is (usually) pink but slight applied pressure makes a white spot, and as sub cutaneous arterial blood pressure pulses, it modulates the reflected light very slightly at heart rate.

It's a simple idea, but made more difficult to make work, because of the differences in ethic skin colour of people around the world, and their vitality.
The light source needs to slowly self adjust, and the received signal pulsations can vary over a wide and constantly shifting range in amplitude.

You cannot just buy a plethismograph sensor plug it in, and expect a strong usable heart rate signal. It needs a circuit associated with it that constantly self adjusts to changing conditions, and hugely amplifies the very small cyclic optical changes up to something usable.

Unfortunately brand X plethismograph probably needs a circuit different to brand Y plethismograph, and its the sort of thing you really need to develop yourself, unless you can shamelessly plagiarize something.

Its been well over thirty years since I worked in biomedical electronics, my memory grows hazy about the exact details, and I really have nothing with me here except the most general type of information from an ageing memory.

An internet search might turn up something. I am sure someone somewhere has already been down this particular path.

The only remark regarding to the use of some I2C-based sensor is that according to its original electric specification, must be placed near to the uC, but according to the link above, the whole circuit ( probe+CPU ) is intended to be at the same case, right ?

Concerning to the temperature sensor, we've already used an PT100-based, and if you perfer another kind, must be aware that parts which are in contact with human body and if this equipment is for collective use (ie, shared between more than one person at a time), the same should support autoclaving, meaning that must withstand sterilization temperatures of almost 150 oC.

Hi All.

I had some more study on the Bio-Sensor.

Here, if I use SFH 7051 then it don't have Analog-Front-End internally. So I need use use additional AFE such as TI's AFE4400. Am I right?

But I found another HRM Sensor "MAX30100", which have integrated LED's, Photodiode as well as Analog Front End. So it provides digital I2C interface. Do you think it will be a good choice?

Please note my project is for Wrist Band Sensor Device ... I am confused if "MAX30100" is suitable for Wrist application.

Looking for your suggestion.

Thanks in advance.

Regards.

I suppose you could ask Maxim.

Wrist is a bony area, it might be difficult to compress the flesh in a consistent manner, but you could certainly try it.