The signal can thus be divided into two portions: a DC portion (representing the absorbance at the specified wavelength of everything but the blood), and an AC portion (representing the absorbance at the specified wavelength of the blood). The detector signal for both LEDs pulses in time with the heartbeat of the patient. These are alternated on/off, and the Arduino records the result from the detector on the opposite side of the finger from the LEDs. Our device uses a dual LED (two LEDs on the same chip) for the 660nm and 940nm wavelengths. Using LEDs of both wavelength, the relative concentration of each can be calculated to find a %O2 for the blood being measured. For deoxygenated hemoglobin, the best wavelength is about 940nm (Infrared). For oxygenated hemoglobin, the best wavelength is about 660nm (red). When measuring concentrations using Beer's Law, it's convenient to select a wavelength of light in which the sample absorbs most. Where: Io = Incident light (before added sample) I = Incident light (after added sample) ε = Molar absorption coefficient (function of wavelength and substance) b = Path length of light c = Concentration of substance in sample The law and its components are described below. In a practical sense, the law says that increasingly greater amounts of light are blocked by increasingly greater particles in a solution. The principle mathematical equation used is known as Beer-Lambert's Law.īeer-Lambert's law is a well-used equation that describes the relationship between the concentration of a substance in a solution and the transmittance (or absorbance) of light passed through said solution.
#ARDUINO PIEZO TRICKS HOW TO#
In order to understand how to build a pulse oximeter, it is first necessary to understand the theory behind its operation. Pliers, Wire cutters, Wire Strippers, etc. We used 220Ω resistors and had a few colors lying around.ĭremel Tool with Routing and Cutting bits (You can get by with a utility knife, but not as quickly) LEDs and Resistors - Pretty cheap if you need to buy them. You can really use anything you think will be comfortable. In step 20 I show my solution to this.įemale Pin Header - These are optional, if you just want to solder wires to the boards it will work just fine.įoam - I used L200, which is pretty specific.
Wires - Including some jumper wires for the breadboard and some longer ones to connect the oximeter to the board.
PVC - Something at least an inch in diameter. In place of this, you can make and order a PCB. Secondary Parts List - Things that were lying around for us, but you might need to buyĬopper Clad Board - Fairly cheap ( Example). we had a bunch of things lying around and bought a few spare parts as well) *(Our Nano is stuck in China at the moment, so we used an Uno, but both will work)
Essential Parts List - Things you probably need to buy (We recommend to have a few spare of each component, especially the surface mount pieces)
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