I am working with a breadboard to quickly test connections on the Raspberry Pi. I have added multiple cables, transistors and resistors to the breadboard to create my Smart Home and everything is working as I want.
Now I would like to put the Raspberry somewhere and leave it there for the next years. How should I do this? Is it necessary to remove the circuits on the breadboard and solder the cables directly to the Pi? Or can I leave everything on the breadboard?
This is not strictly a Pi question, and the simple answer is it depends.
The cheap breadboards have quite reliable connectors (if not up to the standard of traditional IC sockets with gold plated contacts). Their performance is strongly dependent on their history - if they have been used for oversized wires the contact will be unreliable, as will contact with small leads, such as used on transistors.
There is little mechanical stability; traditional components are OK, but modules e.g. SD Card modules, Temp/Humidity sensors are a potential problem.
The major risk is flying leads and interconnections are the weakest links.
I often use a hybrid approach. For example I have a hot wire controller (using an Arduino, not Pi) build on a mini breadboard, connected to a traditional circuit built on Veroboard with high current components, power MOSFET, power supply components. This is quite reliable, apart from the interconnection between the two.
I came from the electronics world into computing (many years ago) and find that a lot of people are treating rpi, breadboards and the various add-on boards as the final solution rather than what they are intended for: a research tool or prototyping system. The idea is that you build the prototype, get it working and then transfer the design to a custom-made board.
In a professional development environment that is how it works. In the amateur world, transferring the design to custom boards might be a step to far, simply because it is a whole new world: electronic circuit design, chemical processes during masking (sodium hydroxide) and board etching (ferrous chloride or ferric, I can't remember off-hand).
That said, I would still transfer the design to a soldered prototyping system like strip-board. Soldering components and wiring secures them both mechanically and electrically. This solution will last years as long as your system is not sensitive to component values deteriorating over time. You would still be wise to enclose the circuits in a box to keep them clean and away from moisture. Leaving a prototype with flying leads and loosely held components for days will likely end in failure never mind years.
Have fun!
There are a few alternatives that you should look into. Besides having a custom board built for you (either professionally or through a site that allows you to upload your own circuit), you can talk to someone at a local makerspace or use a prototyping board.
Some makerspaces have the ability to make custom boards and, through various techniques, can make professional quality boards. The makerspace I use has a laser cutter that we have used to produce high quality boards, but we've also done it with CNC machines as well as traditional DIY "draw it on with a marker" methods.
There are also prototyping RPi hats or more generic boards that already have holes pre-drilled. Making traces is done by bridging the holes with solder or jumper wires. It's still crude, but better than a breadboard.
I briefly mentioned it earlier, but there is software you can download to design your circuit board so that you can upload it to companies that'll make small quantities of your board for just a few dollars. Eagle is the name of one of those pieces of software. The sites don't give suggestions or support, they just make the board and send it to you. Some sites may offer help for extra money. I can't remember any sites specifically ATM, but Google is your friend. :-) A good keyword search start: "circuit upload custom board".
With any of these options, I would suggest getting a project box. A makerspace with a laser cutter should be able to cut an acrylic one for you pretty easily. Makercase.com makes that even easier. Buying a premade one from Amazon or eBay also works.
FYI, as a professional computer tech of many years, I had to explain to many people that dust killed their computer. Some dust short circuited things, other dust acted as an insulator to power starve components, and most other dust prevented proper cooling. Keeping your project protected is key to keeping it running.
If you aren't aware of any local makerspaces, there's a map of them that's kept fairly current. http://themakermap.com/ Makerspaces tend to have some really smart people, so you might find someone(s) of like mind to work with and maybe even give you pointers on how to improve your design. Depending on your experience, you might be able to help them instead.
I think you're confusing two things. One is the circuit on the breadboard and the other is the way that board is connected to your Pi. The other answers so far (and I agree with them) suggest soldering the custom circuit components somehow - either on a custom printed board or on a strip board. I would think in your case a strip or perf board of some sort would be fine.
When you do that, you can solder pins onto your custom board just like there are pins on your Pi, and then you can connect the two of them with jumper cables. That should be pretty stable. Alternatively you can put female headers on your board and plug it directly into your Pi as a "hat".
I personally would not solder anything to the Pi itself.
