Pulse Oximeter From LM324, LED, And Photodiode

This pulse oximeter is so simple and cheap to build it’s almost criminal. The most obvious way to monitor the output of the sensor is to use an oscilloscope. The poor-man’s stand-in for that is a sound card, which is what [Scott Harden] demonstrates in his write-up.

It uses a concept we’ve seen a few times before. The light from an LED shines through your finger and is measured on the other side by a phototransistor. It’s that light grey plastic thing you see on a patient’s finger when they’re in the hospital. [Scott] went with a common wooden clothes pin as a way to mount and align the sensor with your finger. It is monitored by the simplest of circuits which uses just one chip: an LM324 op-amp. There are three basic stages which he explains well in the video after the jump. The incoming signal is decoupled before being fed to the first amplifier stage. From there it is fed to an adjustable low-pass filter to help eliminate 60Hz noise from AC power in the room. The last stage amplifies the signal again while using another low-pass filter in parallel.

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Robo Doc Reads Children’s Pulses Without Scaring Them

[Markus] recently took his 14-month-old daughter to the pediatrician for a routine checkup. During the examination, the doctor needed to measure her pulse and quickly clamped an infrared heart rate monitor onto her finger. Between the strange device clamped to her finger and incessant beeping of machines, [Markus]’ daughter got scared and started to cry. [Markus] thought these medical devices were far too scary for an infant, so he designed a funny robot to read an infant’s heart rate.

[Markus] liked the idea the Tengu, a robot with a LED matrix for facial expressions, and used it as inspiration for the interface and personality of his RoboDoc. To read a child’s pulse rate, [Markus] used a photoplethysmography sensor; basically an IR LED and receiver that reflects light off a finger bone and records the number of heartbeats per minute.

The build is tied together with a speaker allowing the RoboDoc to give the patient instructions, and a servo to turn the head towards the real, human doctor and display the recorded heart rate.

We think the RoboDoc would be far less disconcerting for an infant that a huge assortment of beeping medical devices, and we can’t wait to see [Markus]’ next version of non-scary doctor’s tools.

DIY Pulse Oximeter

This pulse oximeter turned out very nicely. It is based around a Freescale microcontroller and detects pulse as well as oxygen saturation in your blood. The sensor is made of two wood pieces and allows two wavelengths of light to be shined through your finger. A sensor picks up the light on the other side of your stubby digit and the readings are compared to calculate saturation. Check out the finished project after the break.

We saw an Arduino-based oximeter a few months ago. These kind biometric hacks are rare around here. If you’ve got a well documented project don’t forget to tell us about it.

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Pulse Oximeter

[Mike] is building his own Pulse Oximeter which uses light to measure the oxygen saturation in blood. One collateral benefit of this measurement is that pulse rate can be calculated from the same data. The parts used for the detector include a red LED, infrared LED, and a TSL230R light intensity measuring chip. As explained in the video above, each LED is shined through the tip of your finger and onto the light sensor. The IR LED is used as a baseline and compared to the red LED, which has some of its intensity absorbed by the red blood in your finger. This is a pretty approachable biometric concept so you may want to start here before moving on to more involved biometric interfaces.

[Thanks Russ]