This article was submitted by Brandon Uhlig as part of the “Hobby parts for articles ” program. Brandon receives a Modern Device Company Bare Bones Arduino Kit for this fantastic article. Let Brandon know that you appreciate articles such as this by posting a comment. I hope to see many more articles like this one here at uC Hobby.
Scrounging for parts is a great way for hobbyists to save some money. You can get tons of parts out of discarded or unused electronics. But how do you identify all those parts? This article will give you some ideas on where to start.
The focus will be on common reusable through-hole components hobbyists will be most likely to scrounge and re-use.
Obviously, this is by no means a complete list, there are way to many different electronic components to put into a quick guide, but maybe this will give you some ideas to narrow down your search on an elusive component.
Resistors are one of the most used components in a circuit. Most are color coded, but some have their value in Ohms and their tolerance printed on them. To identify values, you can check out the Electronic Assistant software found in the Free Electronics Hobby Software article here on uC Hobby, or find one of the many online tools. A few of them can be found at http://www.electronics2000.co.uk/ in the Calculators section. A multimeter that can check resistance can also be helpful, providing the resistor is already removed from the board (measuring it while still soldered in can give inaccurate results, due to connections with the rest of the circuit). They are typically marked with an “R” on a circuit board.
Potentiometers are variable resistors. They normally have their value marked on them, normally marked with the maximum value in Ohms. Smaller trimpots may use a 3-digit code where the first 2 digits are significant, and the 3rd is the multiplier (basically the number of 0’s after the first 2 digits). For example, code 104 = 10 followed by four 0’s = 100000 Ohms = 100K Ohms. They may also have a letter code on them indicating the taper (which is how resistance changes in relation to how far the potentiometer is turned). They are typically marked with an “VR” on a circuit board.
Capacitors are also very commonly used. A lot have their values printed on them, some are marked with 3-digit codes, and a few are color coded. The same resources listed above for resistors can also help you identify capacitor values. They are typically marked with an “C” on a circuit board.
Inductors, also called coils, can be a bit harder to figure out their values. If they are color coded, the resources listed for resistors can help, otherwise a good meter that can measure inductance will be needed. They are typically marked with an “L” on a circuit board.
Crystals and Oscillators are also fairly easy to identify by sight. Most are clearly marked with their operating frequency printed on them. They are typically marked with an “X” or a “Y” on a circuit board.
Relays are typically enclosed in plastic, and many have their specs printed on them. They are typically marked with an “K” on a circuit board.
Transformers are normally pretty easy to identify by sight, and many have their specs printed on them. They are typically marked with an “T” on a circuit board.
Batteries are also pretty easy to identify, and are well marked with their specs.
Fuses can be easy to identify, and typically have their voltage and amperage rating marked on them.
Semiconductors, such as Diodes (typically marked with an “D” on a circuit board).
Transistors (typically marked with an “Q” on a circuit board),
Bridge Rectifiers (typically marked with an “BR” on a circuit board)
Integrated Circuits (typically marked with an “U” or “IC” on a circuit board), can take a little more work to figure out what they are. Many different types can use the same packaging, so they all can’t be identified by just their looks. In most cases the information you need is found in the device’s datasheet. The datasheet is a document containing the specs on the device and many will include example circuits, links to app notes, and other valuable information. They are typically in a .PDF format. If you have never used a PDF file before, you will need a PDF reader to open it. A couple of free ones can be found below.
http://www.adobe.com/products/acrobat/readstep2.html (Adobe Reader)
http://www.foxitsoftware.com/pdf/rd_intro.php (Foxit Reader)
To find a datasheet, you first need to find some info on the part. Luckily, they have part numbers which can be used to help identify them. They may also have the manufacturers logo on them. Finding the manufacturer can be extremely useful as the most up-to-date information is usually available on their website. For help in finding the manufacturer based on their logo, check out the following sites. They also include links to the manufacturer’s websites. Datasheets can normally be found under the support/download section, or you can put the part number in their search bar.
http://www.classiccmp.org/rtellason/logos/semiconductorlogos.html
http://www.dialelec.com/semiconductorlogos.html
http://freespace.virgin.net/matt.waite/resource/logos/index.htm
http://www.chipdocs.com/logos/logotypes.html?ReR=GG&ReR=GG
If you can’t find any information on the manufacturer, or are unable to find a datasheet on their website, you do have a few more options. There are several search engines on the web to help locate datasheets. Some free ones are listed below. You can search by part number, or even by a partial part number.
http://www.datasheetcatalog.com/
http://www.datasheetarchive.com/
If those fail, you can try using a search engine such as google. Adding “pdf” to your search string can slim down the results, reducing the amount of sites just selling the part with no other useful information. There is also a chance of finding no information on a particular part. Some manufacturers will produce special order parts with “house” numbers, which can mean nothing except to the company that actually purchased them.
There are also many other components you may want to scrounge off a board, but may be difficult to find specific information on. They may not be marked, but you can find some good general information on the web to help you out.
And now for a little test 
See how many components you can identify on the following board. Answers can be found by scrolling below the board - No cheating!
Answers——————
1 Diodes
2 Piezo Buzzer
3 Transistor
4 Transformer
5 Relay
6 Inductors
7 Integrated Circuits (IC’s)
8 Capacitors
9 Crystal
10 Resistors
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