Sheesh, a whole bunch of negativity here.
I haven't built my own avionics, but I do a lot of building of electronics for other activities, and I've thought a lot about the issues, so here's my take on your question.
1. If your rocket is going to stay below Mach 1, life is easier. A big gotcha for rocket electronics is that, around and above Mach 1, there are shock waves moving around the rocket that can cause Barometric sensors to measure that you've reached apogee, or are perhaps going down, causing them to release parachutes early - and most parachutes don't handle opening well when the rocket is going that fast. Commercial and good amateur avionics will prevent ejection if the rocket is going fast, but getting this right is tricky.
2. If you're using commercial Arduino boards, you'll have to be careful about the connections between them - there can be a lot of G force and vibrations when a rocket motor is firing, which can cause intermittent connections for some connectors. At the very least, you should use screws to hold the boards together so the connections don't flex. I've found that using a 3D printer to build a sled that the avionics get screwed to is remarkably useful.
3. I can think of several different methods for detecting apogee on a rocket - barometric, accelerometer, GPS altitude. For all of them, you'll probably have to consider what's gonna happen at apogee, and develop the appropriate algorithms to filter the raw measurements to detect apogee. For example, an accelerometer is great - but it's very unlikely that your rocket will be vertical after burnout, so you'll have to calculate acceleration as a vector with [X,Y,Z] components. You'll also have to note that, after motor burnout, the rocket will be in free-fall - you'll essentially be measuring a 1G acceleration towards the center of the earth until such time as the rocket impacts the ground. How do you detect that vertical velocity is zero at apogee?
4. When you fire the ejection charges, there's a good chance that you'll see a dead short across the igniter wires. If enough current flows, the battery voltage may drop low enough to reset your processors or confuse your sensors. How do you handle or prevent this?
I think building avionics would be a fun thing to do, and a great experience. I encourage you to give it a go - ask specific questions here ("I'm building my own flight computer, and I'd like suggestions on how to prevent the current surge when firing the ejection charge from resetting my processor"), and you'll likely get good answers. From a practical perspective, I would suggest that building and flying your rocket using a commercially available avionics board while testing your own device with no ejection charges would be the safest approach with the highest likelihood of success. From a cost standpoint, build one or two (or three, or four, depending on your success rate) cheap, throwaway rockets that uses cheap 'B' or 'C' motors to enable you to do a dozen or more test flights without worrying about accidentally destroying your big rocket. What you don't want to do is build your avionics, build your expensive rocket, put them together and light an expensive motor, then not have the ejection charges fire.
I'm sure you've done this already, but searching with Google for "arduino rocket flight computer" got a ton of links to avionics projects people had built with Arduinos. For example, this guy (
https://www.altduino.de/) had a great writeup on his development project, showing using his arduino first for data logging, then advancing through a testing regime, all using cheap rockets.
For cheap commercial avionics, you couldn't go wrong with an Eggtimer Quark kit (
https://eggtimerrocketry.com/home/altimeters-av-bay/) for $20 US. You'll need someone with the skills to solder surface-mount components onto a PCB, but that should be available somewhere at your university. Getting one into your country might be a problem, or might not - but it's another one of those things that you could ask a specific question here ("I can't get an Eggtimer Quark shipped to my country; can someone buy one and send it to me and I'll reimburse you?") and perhaps get help. If you phrase it well, you might even get someone to loan you one with the promise that you'll ship it back (assuming that it survives your testing program).
One thing you might consider is posting information about your project in a "build" thread - "We're a university team in <country> building our own rocket and avionics for a competition. Here's what we're doing, does anyone know how to solve this problem? We need an altimeter for testing and development of ours, can anyone help us out?". If you provide enough information, pictures, and interest, you can get enough of a following that you'll certainly get lots of armchair advice, and perhaps more. Right now, you've given us almost nothing to be interested in, hence a lot of people just pissing on your parade.
Good luck, hope to hear more from you here.
There's very little in rocketry more dangerous than a rocket coming in ballistic and you don't know where it is.
