Identifying the parts I need for my first project - Page 1
Forum section: electronics / beginners

author: cryptyk
author_rank: Contributor
timestamp: April 07, 2015, 03:58:21 am
content: Hi! I'm a professional software engineer who just got my first Raspberry Pi. I bought a kit that had some resistors, LEDs, buttons, and a breadboard. I'm so totally hooked. I feel the same way I did when I first learned to program!I'm getting a couple of books to get a solid foundation, but was hoping you guys could kick start me on my first non-trivial project. I have the software already written and everything working on the breadboard. I've just bought a soldering iron and a prototype board and I'm ready to turn it into a real piece of hardware.The problem is that I don't know *really* what parts I need.1) The kit I bought had two "sizes" of resistors: 330ohm and 18kohm. These work fine with the LEDs in the kit, but I feel like there's a "correct" LED/Resistor combination for 3.3V, but haven't found an answer yet.2) I'd like to solder down some connectors on the board, then have two wires on the other end of the connector so I can extend the LEDs and buttons off the board by about 10 inches. There's about 400 different options of connectors I've found, but I don't know what the "right" thing to use is.3) I'm not sure what gauge wire to use. Stranded or unstranded?Lastly, I'm wondering if I'm over thinking all of this. I just want to get it correct the first time around.Thanks!Ryan

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: April 07, 2015, 04:38:39 am
content: 1) We hardware types call those "values". Sizes would be the physical package. Resistors come in all sizes, like your floorboard heater, or 01005 (dust particle), or integrated on chips (germ size). There is no answer because there are thousands of LED types, colors, light output, etc. An 18K resistor would not light a LED very strongly IMO, how are you using them?2) I don't know, do you want to permanently connect or have something removable? What's fun are screw terminal type, no soldering needed. Dunno what would fit on the Pi. There's more than 400 connectors...3) 22 gauge is a good standard size. Stranded. Unstranded will snap apart after a few bends, and are unpleasantly stiff. They are good for temporary connections on solderless breadboards.

author: Tyrian
author_rank: Contributor
timestamp: April 07, 2015, 05:57:44 am
content: Hi cryptyk! I'm an electrical engineer who later got into software! We're basically opposites!1.) There is a "correct" way to calculate a resistor for an LED. The formula you're looking for is R = (Vcc - Vf) / I. Vcc is your power supply voltage, Vf is called the diode's forward voltage, I is the current through the diode, and R is the resistor value. Vcc and Vf are dictated by your circuit, while I is a parameter you pick. I usually use about 2-5mA for LEDs, depending on how bright I want it. When you get your R value though, you'll notice it won't match a standard resistor value. Just pick the nearest value and you should be just fine. If you're starting do design your own stuff, you might want to grab this resistor kit from SparkFun:https://www.sparkfun.com/products/10969The resistors in the 100's range are good for LEDs and the higher values are useful for amplifiers later on.2.) Start with a set of male headers, like these:https://www.sparkfun.com/products/553Break off however many you need and solder them in and you're good to go. Then you just stick your jumpers on the pins and run them to wherever.3.) I second the 22 AWG wire suggestion above. Solid core 22 is good for breadboards, but stranded is good for soldering. Some hookup leads like these may also serve you well:https://www.sparkfun.com/products/11710IIRC, the Pi has male GPIO headers, so female/female jumpers will work with the headers in 2.Also, everything I linked above is from SparkFun. They're a really good outfit that caters towards people who are starting out in electronics or need weird or hard to source parts. They're a little more expensive than regular suppliers, like Mouser and DigiKey, but not by much. Also, a lot of their stuff is geared to be beginner friendly.EDIT: Also, don't worry about getting it right the first time around. Blowing up (cheap) stuff is half the fun!Happy Hacking!

author: cryptyk
author_rank: Contributor
timestamp: April 07, 2015, 08:11:20 pm
content: You guys are awesome. Thank you for the warm welcome and patience answering my "dumb" questionsI'll post pictures of the project as I move it forward!Thanks,Ryan