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Pulse oximeter Mk II

I just started to build a second version of a pulse oximeter. If you don't know what a pulse oximeter is, here is a simple but detailed description what a pulse oximeter is and how it works.

The first thing I wanted to do is to be able to adjust the brightness of the red and IR LED by code. This is very important for calibration of the pulse oximeter. If the LEDs are too bright, it will blind the photo diode. If the brightness is too low, no signal can be obtained as well. This is achieved with a MCP4921, which is a 12 bit DAC with an SPI interface and a constant current drive circuitry (op amp, NPN transistor and two resistors, see  circuit diagram below). The first video shows the brightness adjustment of a red LED.

Reference: Arduino & MCP4921 (German)

I will update this blog as soon as progress is made.

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Good idea but I guess it is not suitable for boxing...

It's funny you say that.  For a bit now I've been working on combining my projects into a pulse sensor meant to be used when I'm boxing.  Not while sparring, but specifically heavy bag work.

  1. ATtiny Bitsy Spider
  2. Pulse Sensor
  3. 365 mAh 3.7 LiPo -- Meant for Bluetooth headset
  4. Oogroo

The idea is to make the PCB the same size as the battery, then, wrap all but the LED, sensor, and micro-usb (meant for a charging circuit using the MCP73831) in oogroo.  The oogroo will be shaped with a metal coat-hanger wire in the middle to be fitted around the ear, with a clip will hold the LED and sensor against the ear-lobe.  The code will read the pulse, translate it into a per minute rate, then transmit it via BLE.  Overall, I believe the sensor could last for hours on the battery actively reading.  There will be no on-off button, since the entire circuit is flipped on by the HM-10's connection status.  And the HM-10 can actively search for a connection on a coin cell battery for years, so "they" claim.

I've prototyped all the pieces, now I just need to buckle down and put them together :)

Of course, it will never compare to the robustness I'm sure your system will inherit.


Video please :) Btw, which weight class are you, Ladvien?

"Robot Builder Obese" right now. And boxing, I admit, is my second choice. I spent a lot of time in Taekwondo (well, a Texas variant). Sadly, it is leg heavy and my knees got jacked up. So now, boxing is attractive, since I still get to hit stuff and my legs don't have to go above my waist. I've been on a medication for the last year that put on thirty pounds. I'm off now, so it's time to get fit again. Another reason I was building the pulse sensor :) So, lightweight here I come? I should have it done in the next few months--I hope. Depending on whether current projects give me trouble.

Use my Micro Magician,it will fit in those gloves and then you can use the accerometer to count how many punches you throw and warn you if you let down your guard :P

I'm guessing you've become a vampire and like your blood to be fresh :p

I had a quick read through the explanation of how the pulsed oximeter works, sounds like an interesting project. I suspect this device should also be able to measure your heart rate making it ideal for monitoring your body during a training session to ensure your blood oxygen and heart rate stay within safe limits.

If you really wanted to go extreme then add a bluetooth module and have the whole thing powered by a small LiPo. Build it into a glove and have it transmit the data to your mobile phone. Next thing you know Nike will steal the idea.