Can I capture the data from a device it's way to the display, after it has been delt with by the circuitry?

I am looking to hack a complex device, so let's start with something simple...I want to take a pulse oximeter that measures blood oxygen levels and pulse rate, and use this data with my arduino.  Is it possible to capture the data from the pins going to the display and use that? Any help would be appreciated, I don't even know where to start, except testing for voltage on pins and frying things.

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orksecurity6 years ago
What kind of display? If it's a simple LCD or LED, possibly. If it's a CRT, you'd have to first do a video capture (at least well enough to get the area which has the information you want) and then analyze the image to extract the data.

May I suggest that you instead consider having the Arduino read analog data directly from the finger or ear clip, calibrating that against the readings you get from a pulse oximeter?
anfractuosities (author)  orksecurity6 years ago
Thanks for the quick replies! The pulse oximeter was just an example. It is a simple LED display. The reason I was looking to grab the data on it's way to the screen is because the noise has been filtered out and everything is already calibrated properly....maybe I'm on the wrong track here, but I did try making my own pulse oximeter with just a set of sensors with no success....The data was all over the place.

But

What I am actually interested in is a system by eaton called home heartbeat. I found it for really cheap, and it is basically a series of wireless sensors that communicate to a base station, which in turn communicates to a "key" that has an LCD display. If I can hook up my arduino to the key, I can have wireless sensors on the cheap!

I did just realized though, that There is a simple solution to my problem. The key has a vibrate motor in it that buzzes when a sensor is tripped...That is where I can make my connection.

Thanks Guys!!
If you want to interface to the Home Heartbeat, why not use the ftdi USB serial port on the base station. There is some documentation available that will help you grab the status from the various sensors:

http://www.kolinahr.com/documentation/home-heartbeat/state-table-of-the-eaton-home-heartbeat/
frollard6 years ago
Someone recently did some research and a pulse oximeter is REALLY easy to do.

It's 2 leds, one visible and one infrared.

They shine thru the finger and hit a phototransistor.

By measuring the difference between the 2 leds (they pulse separately one after another hundreds of times per second) you can calculate the pulse rate and oxygen content with some simple math. By using the 2 different colours you can a) find the pulse rate because reading the difference between led on and led off during a pulse and no bloodflow will eliminate the flesh in the sensor and just measure blood.
The difference between red and infrared light is red is blocked by darker 'bluer' blood while blood is transparent to infrared regardless of oxygen.
The more red:infrared ratio, the higher the oxygen content.
The amplitude delta and frequency on the readings indicates the pulse rate.
so...
in conclusion, there is no 'data' being sent - the device is 'dumb'. All the brains are in the reader portion, not the finger portion, which can be driven directly from a microcontroller with decent adc.
... which is, essentially, what I suggested but stated in more detail so one can build one's own transducer. I'd call that a Better Answer.