Hello everybody, this is my first time on here but y'all seem to be the type of group I've been looking for. I'm a medical student doing research and I'm trying to build my own invasive pressure monitor. I have a monitor now but it only monitors one channel, I would like to be able to monitor multiple channels(transducers) and also to somehow graph, log or export the data. I've got to come up with some sort of analog voltage to digital interface, and then port it into a program that can then take that voltage and record it. It really doesn't seem that incredibly hard but I don't know the easiest way to do it. One of the problems I have is that I want to be able to plug different types of transducers into it, ie blood pressure transducers that measure differences in resistance, electromagnetic flow meters, etc... all will need a 5 volt excitation voltage sent to them. Also, having a way to calibrate the inputs would be required. I like the idea of the raspberry pi being able to display onto a screen, that would be very nice, and it would make data logging very easy, but I don't think it does analog inputs? I may just need to use an arduino as a usb interface into my laptop and then program from there? My level of expertise is just enough to be dangerous! haha. I'm not a computer engineer, i've built a few websites in HTML and javascript, touched PERL a couple of times and I'm shaky with a soldering iron, the closest I ever got to this was halfway finishing the Cisco Certified Network Engineer course in high school. And I've got a budget if less than $250 max, preferably less than that even. So any help y'all might have would be greatly appreciated! Thanks!
thanks for the suggestion, that's definitely down the right track. But I'm probably going to have to go with some of the national instruments stuff though. I dove into the tech specs on my current transducers and I need a sensitivity of something on the order of .1mV to be accurate to within 2 mmHg of blood pressure. Sooo... that looks like a much more expensive chip as most of these 10 bit chips are set at +/- 10V which would give a sensitivity of something like 230mV if I've done my math right, even the 10 bit ones set at +/- 1V are only down to 23mV, so I probably need a 16 bit chip which is $$$.
Firstly, I hope you really meant "non-invasive" rather than "invasive". Invasive tends to mean putting things inside the body (invading it), and is a whole nother level of complexity to simply trying to measure things from outside the body. Trust me, you ***REALLY*** don't want to go there unless you absolutely have to!
Even a non-invasive blood pressure measuring system has some VERY serious safety implications. Typically, you do not want ANY electrical contact to the body, lest a fault condition cause a dangerous current to flow which can rapidly electrocute someone. If you do have to have an electrical contact with the body, you typically have to have multiple levels of isolation between the AC power line, or between any sources of voltage or current which could impose a lethal current. That typically means either low voltage, battery operated circuits, or a truly horribly expensive/complex power supply (An ordinary wall-wart is NOT even close to being safe enough for such a system!).
In this vein (if you'll pardon the pun), that's the reason that a lot of blood pressure monitors use an insulating pressure cuff which transmits the blood pressure information via air pressure, rather than squeezing an electrical sensor up to the body.
The problem, of course, is that the more layers of indirection there are, the more chances for errors to be introduced, and the less the accuracy. And, it also introduces calibration issues, especially with regards to temperature, humidity, ambient air pressure, etc.
Now, having said all of that, some of the suggestions that Alan has made are quite appropriate.