After I made the pressure sensor, it was time for me to work on the big picture of the Stratos III electronics. See, the pressure sensor was a nice little project to get a beginner started with the tools we use; but most of the work lies in the more complex parts of the rocket (no surprise). So for us, that is the Flight Computer (FC), which we design ourselves to fit our needs.
I was assigned to work on the Measurement & Actuation board, which is the part of the FC that takes in all the sensor data and decides when the rocket should activate for example the parachute or stage separators. Luckily for me, a big part of the schematics was already made, and I had to finish it by looking at the list of requirements for the board. This meant I had to find my way around the board, learn the subsystems and then try to add my part. It was daunting at first, I was afraid I might add one part to the schematics and break another. But I just had to do it and learn from any mistakes. In the end, it turned out just fine, and now I have to start routing the board.
Routing a board means that you go from the schematic representation (clear and concise) to the physical layout of the board (looks messier). The reason we first work with schematics is that it is very easy to spot mistakes and fix them. While the PCB layout may be how the board will end up looking like, it is much harder to see what is connected to what and to change things. This is because we want the parts on the board to be close together. This saves space and thus weight.
Below you can see a screen-capture of how it looks like around the time I start routing the board. I open some part of the schematics on the right, so I know what kind of layout for the components will make sense. For example, you don’t want the power lines to go around all the components, rather it should have the priority over other signal lines. Of course, these considerations change depending on the subsystem I’m working on.
On the left, you can see the (unfinished) representation of what the board will look like when we put it in the rocket. The black area is the board, the things around it are different kinds of components like resistors, capacitors, microcontrollers, etc. All the lines between the components show the connections that still have to be made (routed). Some people call it a ‘rats nest’. You can also see a part of the board that is already routed, this is the power regulation and conversion part. It’s on almost every board within the Flight Computer, and it is there to take the battery voltage and turn it (safely) into usable voltage levels
Hopefully, I can show off the completed board soon. In the next blog, I will talk about a wire-cutter test we did at the lab. Stay tuned!