By my estimate, for about 200-500€ you can get most of the basic components that you'll need as a beginner. Expect to spend more on the tools! It's really a weakest-link situation: if one of the major, important tools is crusty or missing, you can get completely stuck. Only have 1mm solder and a massive, lukewarm iron from the 60's? Ran out of wires? Assembling anything will be such a pain that you're just not gonna bother.
Extra tool suggestions:
Dave Jones of the EEVBlog made a video about getting started with a $330 budget. It's more tool oriented than my document here, which covers mostly the idea of getting started, and eventually hoarding components.
My EE corner. Unfortunately actually a corner, and a bit hard to get to for both me and light. Should buy a lamp... wait, now I can make one. Each drawer is filled with maybe 1*3€ worth of components on average, so a few hundred for a pretty good beginner's supply.
When buying components, I did make some mistakes getting random unusable parts early on, but my orders are getting better and better. At first I thought getting 10 or 100 of some components was a bit silly, but I'm already running out of some. Parts get soldered into prototypes, cable bits, fall under the sofa, get sorted badly, or destroyed (an effective way of learning, as failures tend to stick in your mind). It's also a lot like LEGO. That bag full of pieces empties quickly and amounts to less than you thought.
Also worth to note is that, because delivery is a bit slow, you have to predict what you might need in the future. It might seem worth it to pay more for the convenience of a local supply, but because the China stuff is so cheap you can gamble quite a bit.
I suspect the parcels will arrive a bit faster (and maybe safer) if you get multiple (4~10) things from one supplier. It's a bit of work to bracket your goods into just a few sellers, and you might pay a few cents more, but I think it is good behaviour. If a parcel is too valuable customs might snag it though. I generally keep mine under 50.
Make sure to check prices between sellers, because in odd cases they can vary quite a bit. Be prepared to juggle at least 20 browser tabs. Make sure shipping is more or less free (China/HongKong usually is). If a thing appears cheaper than normal, it's probably because shipping is excluded. Always keep an eye on what the seller is doing with shipping. Also, many listings are strange due to language barriers.
I'm at the point now where Arduino is beginning to feel a bit like an obstacle because it doesn't show everything that's going on and the quirks of the Arduino libraries is not what I'm looking to learn. I don't much like plugging in modules and copy-paste library/snippet code (unless I need to actually do a thing quickly). However, getting silly DIY kits (like a $1 audio amplifier or 555 kit), or little simple modules can be useful as a way to understand which components are needed to make what. I guess it's ultimately about making an effort to understand things. Thinking and designing purely on a module level is likely going to be limiting and confusing.
There are many videos online about electronics projects. The ones I find the most insightful are the basic component tutorial ones (and perhaps repair videos) as those go into the ideas of how things work or why they don't. The least useful ones are more about private, finished projects (I bought these modules, downloaded some libraries, and here I am clicking on webpages or modifying some functions).
When new components arrive it's seemingly a good idea to look up how it's used in a circuit. But, if you search for some-component arduino, the results of that image search will often be circuits which do not work, because people who upload images are often looking for help (why does this circuit blow up my chips???). Many Hexfetians died to bring us this information... *Mon Mosfetma sadface*
It's hard to give general advice here - I don't know where you want to go. So, I'm going to assume you're exactly like me: You want to fool around with electronics and have a few hundred euros or dollars to spend. You're not looking to build a very specific thing, you're just curious.
At this point you may not know if electronics is for you. Getting a starter set is seemingly a good way to get started, but having a large collection of components introduces a synergy which doesn't quite exist at starter set levels. When you have enough stuff in the parts bins it is like having a well equipped workshop - it gives you a worry-free forward momentum when building & playing. But, if you're very unsure about your interest, I'd probably recommend first getting a single <20$ Arduino UNO starter set on eBay or aliExpress (about the same prices).I would perhaps not recommend getting the larger Arduino Starter Sets. Some of the stuff they include is a bit strange and you'll actually pay a lot more for the sorting (plus, beginners can be milked a bit extra).
Only the Genuine UNOs have a golden thingy next to the USB jack... oh, wait.
An Arduino UNO R3 (copy) with an ATmega328P-PU (socketed 28-pin IC) is about <$6 (with USB cable) at the moment. As a beginner, this board is easy to handle and having the chip socketed can be useful later on. The ATmega328* needs a helper chip to talk with a computer over USB serial (and the Arduino IDE that you'll likely be using), and on some boards this chip is missing or is not supported by your OS. Some (most?) UNO R3 boards have an extra Atmel MCU (small square) to do the serial stuff and those work on my Mac. CH340G and FTDI chips (small rectangular) works on linux no problems.
The surface mount (SMD/SMT) board variants are cheaper but the Minis and Nanos require soldering on headers. The Pro Mini has no serial helper chip (an advantage as it reduces power consumption and size). I program that by temporarily hooking it up to another little board with the serial chip on it.
My ORAC, uh, I mean RPi3, and black Sainsmart UNO in acrylic case. I have a RPi 1 too, but use neither. They're just dinky computers, really. Too clumsy to boot just to do some EE experiments.
Max price: About 5€ for an Arduino UNO (the ones with an additional MCU for serial might be more). Nanos and Minis are half that. Loose ATmega328P-PU chips are about 1.5€ or less in bulk. You might need a 16Mhz crystal to go with that if you plan on doing a breadboard version (and 22pf caps). They need to have a bootloader (only costs a few cents extra) or you'll have to burn one yourself, and that can be complicated.
Trying out some coloured headers on the Pro Mini and Nano as they came without. I needed the headers to try the boards out, but really, these boards are more for miniaturising finished projects. It can be a good idea to not solder anything (m/f headers or ribbon cables) on until you know how you'll attach/connect the boards in e.g. a case. As prototyping boards, these tend to... "flap about in the breeze". Without feet, there's a chance they will short against something.
Both are ~2€ from China with the Pro Mini being slightly cheaper. The Nano is larger and mine has a CH340G I believe (programming it over USB works fine on my linux machine.).
Resistors are likely best bought in a set of around 600 (different values) to begin with. Search for Carbon resistor and Set, Assortment, Assorted or Kit. The W figure is how much Watt they can handle (they heat up as they try to "choke" the current). 1/4W seems common for simple stuff. There are cement resistors which are made to handle lots of power, and can be used as dummy "loads" (a dumb brick which does nothing but draws power).
These go in the never-to-be-sorted bin once used. Looking at the magnitude band is the easiest way to roughly identify a resistor if you just need a very rough value.
I've bought sets of both beige/sand colored and blue resistors. I recommend getting the sand-colored ones in an a set as they are much easier to read!!! You could get certain set values of blue, like 10KΩ, which is common for "pulling to ground". There are smaller ones too (1/6W?), so getting those in certain values can also help. Because they're smaller, some <1KΩ values might make sense, like 330Ω (striking orange) and 750Ω? Could be useful for LEDs in low power situations, but mostly to help with identification when sorting/searching.
I had these A5 binders and decided to sort out the resistor situation. I just taped them onto printer paper, and... made a few mistakes with the holer. I feel really stupid just looking at it.
So, I decided to make a proper solution high precision with stamp-book pockets. I spent a fair bit of time prototyping these. As it turns out though, effort does not necessarily translate into quality. The resistors just keep falling out and dropping the binder would be catastrophic. Turns out the first solution was more efficient so now I feel stupid again.
Resistor networks are convenient when you need multiple same-value resistors in a certain arrangement, but they are a bit specific and I have not used mine much.A thermistor changes resistance based on temperature (more or less depending on variant). There are also light, humidity, etc. sensitive resistors, as well as trimpots/potentiometers. The micro controller can sense resistance and use it as input. Some sensors have onboard miniature microcontrollers though.
Three 220Ω resistors in series add to 660, whilst in parallel they reduce according to a formula... 1 / (1/R1 + 1/R2 + ...). There seem to be a sort of strong nonlinear bias towards the lower value, so in the case of a very big and small value, you can sort of assume the small one. Of course, a 50K trimpot may go all the way down to 0 and behave oddly in a parallel setup. Also try them in a voltage divider setup and see what happens.
Max price: 2€ for set of 600 1/4W Metal film (blue), however, I'd get the sand colored 1/4W carbon film ones which might be a bit more expensive. Resistor sets different series such as E12. Unfortunately many resistors have quite thin leads and won't socket well everywhere.
Just like with resistors, capacitors come in sets. There are two main types to look at first - Ceramic and Electrolytic. These can be found in sets too. Larger ones generally have a larger capacity, and cost more. If you put a capacitor on an LED, it will fade out when you turn the power off. The larger the cap, the slower the fade.
If you have a 12V circuit, a 10V electrolytic would not feel well in there. A 25V would be fine I think, and note that the capacitor itself doesn't discharge 25V just because it says so on it. It's just the breaking point, afaik. Higher V rating is more expensive so that's the incentive to keep it low.
Ceramic caps are hard to read. (Edit: found this handy cheat-sheet.) I recommend sorting them by the first two digits, like 10 101 102 103 104, or 223, 224 etc. The third digit is the number of zeroes. Unfortunately my 100nF/104 (brown ceramic disc) cheap ones measure at 50-60nF. I guess the cheap ones are not that accurate. The sand/yellow monolithic ones are more accurate (newer technology). Green ones are poly-caps and I've seen them used on old audio boards.
Ceramic disc ones with black dot on top are supposedly more temperature independent /stable. Finally, as I understand it, small ceramic caps are used to filter high frequency noise. Large electrolytic ones take care of big dips and wobbles, but are slower to respond. Combined they compliment each other (e.g. smoothing the output of a small power supply). It's also common to see something like a 100nF capacitor near the GND and VCC pins on some ICs, helping to smooth out fluctuations in power due to circuit complexity.
Electrolytic caps have a polarity (the band one one side is (-) GND). Just like ceramic caps, they work as small batteries. Large ones can hold quite a charge for a long time, and really large ones can be deadly if not drained before tampered with.
Max price: I think it's advisable to get sets of these initially, as there are many values to cover. Sets range between 1.5€ and 4€ for 300 or 1000 ceramic, bagged. Looks like 3-4€ for a set of 120-210 electrolytic. Some sets don't include larger values as they are more pricy. This explains the price differences you might be seeing. Getting some 100nF monolithic (104, yellow) ones could be a good idea as those are commonly use in "decoupling" and have a more reliable accuracy (<1€ per 100).
There are other types of capacitors, like metal film, poly, tantalum, monolithic. Quality capacitors cost more, but as a beginner the cheap stuff will be fine for mucking about.
You only have one pair of arms (right???) and when measuring/probing stuff with a multimeter you often wish you had another pair. Sure, you can attach crocodile clips, but chances are they'll crush things in their jaws. Test clip hooks are the answer to your problems! They have a small hook which sort of gently clamps onto component legs. However, do not use cheap test hooks or cheap leads with your multimeter if measuring high voltage!
Max price: 1.5€ for a pair (2), or for 10 loose heads. You'll need to solder a cable in yourself (there's no screw like with banana-plugs).
These come in a variety of lengths and colors. I go through a lot, so 10 male and 10 female wasn't enough for me. The female ones are harder to cut, so you might want to get the shorter versions of those. There are also double ones (e.g. 2x8) but you can glue single line ones them together.
Max price: 1€ for 10.
A Light Emitting Diode is a diode which emits light, but tricky folk have also used them as a light sensor! Just like diodes, they block reverse current, and have a forward voltage drop (1-2V, varies). If you try to put 4 in a series on a 3V battery, none will turn on. If you put them in certain parallel configurations (e.g. using a single current limiting resistor on their shared ground), chances are that a few will be dim or not turn on. Tricky!
Max price: F5 LEDs are often 1€ for 100 unless it's a more fancy model (RGB, Rainbow). SMD ones are cheaper. For larger projects you can buy batches of 1000 for <10€. Getting a set with many variants (3-6€) might be a good idea if you're just getting started (you get a handy box too). I haven't dealt with LED strips, rings or bulbs.
Modern LEDs are very bright - so bright they can be blinding if a low resistor value is used, and their glare can be a bit annoying. I've made a hood from foam an plop in on suspects and offenders. Diffuse variants may be easier on the eyes. The more voltage an LED takes, the larger resistor it will need in order not to burn or wear out. You can do math on this, or just go by feel.
RGB LEDs can be common cathode (+B,+G,-,+R) or common anode (-B,-G,+,-R). Somehow I feel more comfortable with common cathode, but a common anode one came in handy when trying out a rotary encoder.
Sidetrack: A rotary encoder has two channels (and sometimes a switch) which go high and low in an overlapping pattern. Here both red and blue are on. Turn a little further, and only red, or blue stays on, depending on direction, then both are off. A micro controller can monitor these changes, making the rotary encoder a good user interface device. A rotary encoder can be spun indefinitely with no stop, and has a sort of digital resolution. A potentiometer is more analog, is usually limited to less than a full turn, though there are 10 turn ones (more expensive). As a side note, I prefer getting both these with knurled shafts, as there are better looking knobs for that.
Max price: Rotary encoders are <0.5€ each, a bit higher for one on a module/breakout board. Potentiometers are 0.2€ each. B50K is common but I could see use for much lower values. 10 turn ones are maybe 1.5€ each, as they are more bulky.
I've ordered more of these. What happens is that you build a thing, then you don't want to scrap it right away for the next thing. Just like LEGO. Get a variety, they are useful for different things. If needed, cut through the double sided tape to detach the dovetail busses.
Floppy long wires can make a breadboard project look messy and confusing, so I recommend getting some bendable isolated wire, or making some yourself from scraps. They come in pre-cut & bent bits (sets), or cut-it-yerself bundles.
A simple 3V coin cell battery offers some mobility and manageability when breadboarding on the go. Might be possible to make use of the double sided tape underneath a breadboard to stick on a battery pack with switch and voltage regulator? There are handy breadboard stick-on power supplies for <1€ with 3.3V and 5V regulators onboard.
Anyways, I like this size of breadboard the best (above). The longer ones are for larger projects. When used for many smaller (beginner) projects, things can get a bit confusing.
A look inside a breadboard. It's really just plastic shelves stashed with conductive metal clamps. There are even smaller breadboards (useful for perhaps connecting a few wires together, testing components), but they all use the same 5-long clamps. I did some experiments modifying breadboards, but found out that some types of glue can be slightly conductive. Note that there's also some capacitance between the lanes in a breadboard, as a capacitor is pretty much two metal plates close to each other.
Max price: 2€ for long one, <1.5€ for short. Smaller ones can be bought in packs of 5 for 2€. There are also sets (long board, cables/wires, power supply for 4€).
At some point you'll reach a point where your breadboard projects will begin to feel like something to save. Regardless, moving them over to prototype board can be satisfying and an opportunity to practice soldering. They come in a variety of materials, like glass fiber, paper, and... I think the brown one on the picture here is actually bakelite.
Max price: 1.5-6€ for 10 depending on quality. Get a variety. I find smaller boards more useful as I have no large, complex projects.
None shall pass! Oh, you're heading the other way? Well, alright then.
I use these black diodes when I get paranoid about polarity (for power input) and/or need to drop voltage.
I haven't used these much, but some designs call for them. Zener diodes can be used for certain kinds of voltage regulation (do useful things in reverse). If you watch a diode tutorial on youtube you might feel inspired to get a few of these.
Max price: 1€ for 100 IN400*. Best to get Zener diodes in a set as they vary in value. Germanium ones are more expensive.
I've been trying these out. The black 6x6 are very common but all I've bought are too hard, and you have to force the legs a bit in bread/perf board. Prefer the 3x6 ones (2 legs), if I had to choose. Micro switches are larger, but feel better. More expensive. Will be trying out some Panasonic mouse switches soon. Wish there was a rubber membrane button type, like on joypads. Maybe I should get some Cherry switches?
I'd avoid the "gamey" black and yellow tactile switches, as the cap sits on all wobbly and without they're horrible to push (too hard for typing or gaming). The cap is supposed to be held stable in place by the housing of the project. There are right angle versions of some switches, so they can come out the side of the circuit board.
Max price: 1€ for 100 6x6 tactile switches. Seeing 30 DIP 3x6 for 1€. I've soldered the SMD(/SMT) variant onto glass fiber board, but they don't work in breadboards (whilst the through-hole ones don't work well in glass fiber board). Cheap microswitch variants go as low as 10 for 1.5€ but are generally more expensive. The latching 7x7 switches (white & blue) are 40 for <2€. Very breadboard friendly.
I often power my 5V projects with an USB charger, a computer, a bench power supply, or of course batteries. Some battery holders come with a switch. Using 1.5V batteries, you'd end up with multiples of 1.5V. If 4.5V or 6V is undesirable, you'll have to regulate. Some circuits and chips are quite tolerant though. More voltage allows an MCU to run at a higher clock frequency (perhaps set by an external crystal) (e.g. 4MHz at 1.8V up to 20MHz at 4.5 to 5.5V), but only up to a certain point. An Arduino board often has a voltage regulator onboard, but you can feed it raw power as well, and then you need to be careful about not putting something like 6.4V directly into it.
Four 1.2V batteries will reach 4.8, plus some margin I guess. A fully charged 1.2V battery can reach 1.4V. There's a sort of voltage drop as the battery drains. To squeeze the last drops out of a battery, you can build a "joule thief".
The Arduino UNO accepts 9V input from a 5.5/2.1 barrel plug. The outer barrel is GND (-). Not all devices are wired with the outer barrel as GND. You can always put your multimeter in continuity mode, then touch the outer wiper in the barrel socket to what appears to be the ground plane on the PCB. USB socket casings tend to be soldered to GND as well. Sometimes the DC IN port have a little symbol showing the polarity of the barrel jack.
Max price: 0.2€ to 0.6€ each for holders. I'd get the ones with a switch, to limit cable yanking.
I use these a lot (male more than female). It's a sort of standard for connecting things with wires cheaply. The Arduino headers take male Dupont connectors. Their disadvantage is the lack of physical polarity, i.e. if you make a 2x4 connector, it's possible to plug it in backwards/180.
There are other types of connectors which have physical tabs preventing this, such as XH2.54 and KF2510. If you're making a little programmer cable, or some custom module on a prototype board, I recommend using these. Or, I suppose, you can just put stickers on your Duponts. The advantage with Dupont is that you can plop down your wires anywhere (Arduino headers, breadboard).
Max price: The 600+ piece 6€ Dupont set might be the simpler solution. I actually got all of my pieces separate, I think 200 male, female, then single, double and quadruple housings (comes out about the same price, but without box). Going through it fast. Using the singles and doubles the most. XH2.54 and KF2510 stuff is cheaper as loose parts without wires attached (Only AliExpress has KF2510 boxed sets it seems).
Leaf Switches from angled headers and Dupont connector sprues. Might use for a pinball project.
These come in a variety of forms. Thin ones can't handle much current (melts?). Size is often expressed in AWG, where larger number is thinner (I guess it measures how many fits in a bundle). The metal wire inside can be stranded (several wires) or a solid single wire. Apparently "cable" is used when there are several insulated wires (cores) inside a... cable (or side by side as with a ribbon cable), but not when a wire is just stranded.
Making custom cables is one of the simply but empowering things you can do early on! There's no longer any need to look on amazon for expensive special cables that you need to get an old device working.
Jumper wires... jump between different points? They're handy for quick hookups, especially over distances, but can create a mess if over-used. I prefer using the bendable, solid ones on breadboards as they illustrate better what's going on (short and concise). You can make your own from component legs and old wire peels or shrink tube, or buy pre-made bits, or buy on reel/rolls.
It's a bit fiddly to strip a bunch of these with a side cutter. Edit: They strip nicely in one go with my stripper. Crimping is still quite fiddly though, even with my tool.
24 AWG which I use for simple wires/cables, and "0.75" (21 AWG?) which I use for 12V+ stuff, such as PSU leads. It might be a good idea to get two core cable for making simple power cables, so you don't have two separate wires flopping about. Definitely get some Wire Wrapping Wire, 30 AWG, as 24 AWG is not good for doing fine work under prototype boards, whereas the thin, bendable WWW can really tidy things up.
Max price: Varies, and copper isn't that cheap. 2 meters will run out fast. 5-10 meters is about 1.5-3€. Wire Wrapping Wire in a 305 meter roll is 4.5€. A bit long. There's a multi-color roll that might be a better choice. Multicore cable is a bit more pricey and not commonly sold by the meter by Asian sellers.
If you're having trouble finding thick bendy wire for making breadboard... brackets-looking-things, you can use old component legs. However, those can be too thin and too short. I found some 25-26AWG copper wire in wires for a broken space heater assembly. Some thin shrink-tube on that works nicely. Thicker copper wire can be found old heavy duty AC stuff and phone lines.
When you don't want to solder or bother making a connector, the crocodiles come in handy. I should get 3mm googly eyes and stick on! Might fall off though, as the rubber is very slippery on cheap clips. Anyways, I'd recommend initially getting 10 and modify as needed. To get the hood off, clip onto a header and the hood will go around the back of the metal head easier. You can crimp/solder on new wires. I've tried sanding/roughening up the metal a bit to reduce slip. Unsure if it has any real effect, or just imagined.
Max price: 1-2€ for 10, unless you get just the heads.
These are electromechanical devices using coils. Perhaps speakers should be included here. I have a little summer that is just an electromagnet hammering away. I think regular speakers have an electromagnet which tug on the (black) membrane cone, which displaces the air and creates sound.
Modern motors can be quite complex, requiring precise timing of several pulses. Solenoids are tricky to use too, as they can overheat (e.g. when holding a flipper button), but a workaround is to PWM (strobe) the coil during hold to trickle current into it.
Max price: Varies, but only the dinky versions are cheap. Eventually I might use these for a pinball project.
You can make your own coils using magnet wire, which is enamelled copper. Wind around some ferrite and things happen. Induction is one such thing, and some circuits (such as a joule thief) calls for an inductor.
Old school transformers use large coils. The more windings, the more voltage drop (generating a lot of heat as power is wasted). A primitive transformer might drop the voltage from the AC outlet down to tens, then use a diode bridge rectifier (a simple maze of 4 diodes) to turn it into DC, then use a large capacitor (and maybe some smaller ones) to smooth out the residual AC wobble and "ripple".
Today, wall warts rely more on switching magic, basically, turning on and off very fast taking only small bites.
Some thicker wire around a ferrite toroid core, and a roll of 0.1mm, perhaps useful for lighting up SMD LEDs inside model kits. Have a 0.2mm roll incoming.
Max price: Varies by length and gauge. Copper is not cheap. Inductors come in many forms and values.
Some displays are just large LEDs, and often require an extra chip so they don't eat up all of the MCU's I/O pins. It's a pain to set up. Pixel displays likely have a driver chip onboard, containing a frame buffer and interface logic, taking the load off the MCU. The Arduino community has made plenty of graphical libraries for these, but they're probably a bit bloated as highly optimized stuff is less general.
Video/graphics eat a lot of memory and clock cycles, and the ATmega328P-PU is a bit too tightly constrained for that. I wish there was a 20Mhz MCU/SoC with specs more like a mid 80's computer, having simple onboard VGA output ability and 16 colors. MCU's tend to mostly scale up Mhz and pin count. 20Mhz is plenty fast for game logic, but gets software graphics nowhere.
Max price: Varies. OLEDs are more expensive than LCDs. I haven't used these much.
Shrinks when heated. Used for isolation, durability, and giving a clean look. Slip on wire before you solder on any plugs.
Max price: 3€ for a set with various sizes and colors. I mostly use the thinner bits.
Eventually you might want to move away from using the Arduino UNO board and move your MCUs onto perfboard / prototype board. The ATmega328P is a 28-pin DIP (Dual In-line pin Package) IC (14 pins per side) whilst the ATtiny85 has 8 pins (or "legs"). Using a socket has advantages beyond the obvious - if you solder it on empty, you can avoid putting any heat into the actual IC. Chips with 7 or 8 pins per side are fairly common (e.g. 74 series).
Max price: 1€ for 10.
As your prototype boards, modules and DIY kits become plenty, it's satisfying to have them look a bit nicer, while also avoiding shorts (when solder points are resting on a conductive surface). M3 screws fit most things, but sometimes you'll have to drill a hole up a little. I like the feel and weight of metal. If there is a need to isolate the board thoroughly, it can be done with Nylon screws and parts, or just isolation washers. There are also spacer... plugs... moon-lander legs of sorts.
Max price: Varies. Sets appear to be 3-6€. Look for e.g. M3 set spacers, perhaps adding brass.
Breadboard friendly versions of these likely come in the TO-220 package. The hole in the top metal plate is for attaching it to a heat sink (before soldering so screwing it in won't stress the leg joints). These things generate heat in order to bring the voltage down. In some cases you may want to isolate the plate from the heatsink using an isolator, as the plate is ground and who knows what the heatsink might be touching? But now I'm speculating.
It's possible to find regulators in the TO-92 (transistor) package and various SMD forms, and older metal packages.
Max price: 1€ for 10, though some TO-220 thingamajibs are more expensive.
Used mainly by bench power supplies. Keep in mind that when using them for power and not audio, the shell should be isolated with no screws poking out in case you or something touches them with high power still on. When making cables for your PSU, you might want to use thicker wire that can handle more current and isn't too flimsy.
Max price: 1€ for 10 plastic ones.
I have yet to use one (U._.) but these are apparently important in electronics. Of course, I got the good ones - don't know what they do - but I'm sure they're just great. Their names are BC558, BC548, 2N3904, and 2N2222.
Mac price: 1.5€ for 100.
Nowadays you can do a lot with a micro controller, and if you need more I/O pins you can often just get one with more pins quite cheap, or perhaps a module if you need special features like audio amplification, relays and whathaveyou. But, I think it's fun to fool around with loose chips, so here are a few:
Max price: Much cheaper than MCUs. Some are about 10 cents each.
Nichrome wire is like a resistor, and thus gets hot if bombarded with Ampere. Longer pieces have more resistance. This particular pice of wire needed over 1A to cut the cup. It can also be used as a heating element when bending acrylic glass, or for cutting styrofoam.
Max price: Depends on length and gauge, but pretty cheap.
Look through your box of old broken electronics. When you understand what you see, it's suddenly a treasure trove of parts! Note that older components might be deteriorated, and have different specs. New LEDs are a lot brighter for example.
Old dead 56 modem card I think. Capacitors, Beeper, Relay, fried chicken.
Inside old computer speakers. These take 16V AC so there's a diode bridge rectifier inside. Basically, a certain maze arrangement of 4 diodes (one-way things) can turn AC into a sort of wobbly DC which is then smoothed out by capacitors. If I understand it correctly, capacitors are like hyper batteries, if power on the rail outside is high, they store up to a certain limit, if low outside, they release. This mechanism ensures an even supply on the power rail. Some devices use the AC wobble for timing, but not these speakers, so I successfully put DC into it (needs a bit higher voltage). DC basically solves the diode bridge rectifier maze the same way continuously and isn't converted.
Once you have $50+ of parts, you'll definitely need a storage solution. However, the drawer system requires some attention. Labelling is important. I did draw label pictures, but color codes could make things even easier to find. Structure can actually be an enemy, so I'd recommend getting different brands, shapes and colors of storage solutions. Then you'll remember that, oh-yeah those things are in that thing. Otherwise you'll be lost in a matrix of all-alike cells, with nothing for memory to anchor to.
Another trick is to avoid being overly structured when sorting, even though the mind loves it. If you only have two compartments for Blue, Purple, Orange and Yellow LEDs, don't sort them after color/hue (B+P / Y+O), rather, mix the most different looking ones so they'll be easy to visually identify when picking (B+O / P+Y). The same applies to shape and size.
Storage boxes with rounded bottom compartments might be preferable. Some IC components might be better off in their ESD bags. Save those anyways.
Once you've been hobbying around for some time, you'll have a box of unsorted stuff. It's best to keep a medium sized compartmentalised box on your workspace and only sort coarsely into that (LEDs, resistors, caps, switches...). The advantage of this system is that the box will act as a processor cache, you can look in the cache before having to search your main storage. You can also use it as a mobile kit.
Best to use a round-bottom model as you might be doing a lot of digging for parts.
Save cut off legs and even cable peels. By pushing a leg through a cable peel, you've quickly made an isolated jumper bracket for the breadboard.
The disadvantage with sorting... cabinets with drawers is that you have to pull a lot of them out when searching for stuff. Space efficient though. The cache box often alleviates the search time problem .