I am a complete novice when it comes to electronics and I'm trying to reverse engineer the Bluerobotics PCB for Bar30 pressure sensor, Bluerobotics PCB.
It has the MS5837-30Ba on it and I have a few questions I hope you guys know the answer to.
What kind of diode is in the picture below(red arrow). I did some research on this some time ago and when I revisited the project this week I saw that the old PCB schematic I had made uses a Schottky barrier diode for some reason. I have scoured the internet in the past few days, but I can't find anything that mentions it using this kind of diode. I did find these files on Github Github files, but all I can find about the dioed is that it is a SOD523 package type.
The MS5837s datasheet says to use pull-up resistors on the logic lines. Why does the Bar30 PCB not have pull-up resistors on SDA and SCL? Is this because it is using a low dropout regulator, and the voltage is 3.3V? As far as I can see, it only has a diode, LDO regulator and two capacitors.
Yes the diode is to stop people frying the board by connecting the power backwards. Unfortunately they
neglected to protect the I2C bus pins as well, so idiots can still fry the board by connecting incorrectly. They've
made it easier to miss-connect by not silk-screening the pinout on the pcb!
The lack of pull-up resistors is so you can put many different sensors on the I2C bus and only use one set
of pull-ups - too many pull-ups in parallel may prevent the bus working. So you need to add pull-ups yourself
if necessary with this board.
What can it be besides a diode? The power goes straight through it, doesn't it?`
And if it is a diode what do you think its specs are? And can I maybe just leave it out on my board?
Would it be possible to use this with an Arduino Uno without pull-up resistors, or are they absolutely needed?
If that's a diode, just about any Schottky diode will do just fine.
I2C requires pull-up resistors. The Wire library enables the built-in pull-ups on the I2C pins but they are too weak to be in spec. It will usually work (been there done that) but the moment you use longish wires (half meter or so) it may stop working or become unreliable. I2C spec is 1-10k for the pull-up.
That said, your sensor works at 3.3V, so you must use a level shifter as the Arduino uses 5V signals. Levels shifters normally have pull-up resistors on board.
