When I first started building projects, I found myself using a wide range of different parts. Often times, I would just grab whatever happened to be available or was cheap. This often meant using surplus parts and scavenging parts from retired equipment. Scavenging has always been one of my chosen methods since I get to see how machines are put together plus I get to see what types of parts they are using. If you can, I highly recommend taking things apart as often as you can.
After a while though, I found myself needing to be a little more productive. One step in accomplishing some productivity is to have a stock of commonly used parts that are useful across a wide range of different projects. Rather than hoping that I will be able to scavenge the required part out of some old equipement, I decided to start keeping an inventory of commonly used parts. There are some really great benefits to keeping a stock known parts:
My goal for this article is to describe my favorite parts, and to provide you with some information about how you can obtain these parts.
Here they are, in no particular order, some of my favorite parts and why. The pricing and part information is provided as an example. The pricing is for quanities of 1/10/100 meaning you order 1, 10, or 100 parts.
There a a number of different types of capacitors on the market. For example, there are ceramic disk, polyester, polypropylene, tantalum, and a host of other types. Each has its own unique capabilities. For general purpose use, I have chosen to use Monolithic Ceramic Capacitors. They are typically in .100" spacing. You can, as seen in the photo above, get them in .200" spacing as well, depending on your needs. I wrote an article about Bypass Capacitors last year that you might like to check out.
0.1µF Z5U 50v .100" spacing
|Supplier||Part Number||Pricing 1/10/100|
These capacitors are a real workhorse in my parts bins. I use these capacitors as bypass caps, and also use them in conjunction with the MAX232ACPE and similar parts. These are great general purpose parts. Note however that the Z5U type capacitors have a +22% -56% tolerance, which is pretty loose. However, since the value I use is pretty large, the error isn't significant for bypass use. I use them as bypass caps on all of my microcontroller, and BDM products. As such, I usually buy these in 1000 unit quanities. However, for most people, keeping a stock of 20-40 of them would probably suffice. Note the price differential between Digi-Key and the others!
22pF COG 50/100v .100" spacing
|Supplier||Part Number||Pricing 1/10/100|
The 22pF capacitor is a great part if you like to build microcontroller projects. These are usually used as bypass capacitors for microprocessor crystals. The 22pF value works well with 8mhz - 20mhz crystals. I use them on BotBoards, 68HC12's, PIC's, etc. Note that these are COG rated, which are quite accurate compared to the Z5U style above. I would keep 10 of these on hand.
E-Switch EG1218 SPDT
|Supplier||Part Number||Pricing 1/10/100|
Switches are usually difficult to deal with. If you are breadboarding, most switches won't fit the breadboard. Except, of course, for this one. Randy Carter, a long time member of the Seattle Robotics Society, turned me on to this switch. It is a small, SPDT (Single Pole, Double Throw) switch that actually fits into .100" centers of most breadboards. It even has leads that are long enough for a solderless board. Perfect switch! I recommend 10 of these to anyone. Mouser has a great price on these.
A while back I wrote an article about connectors. I still use the same style Molex KK series connectors, and have had great luck using them in a variety of situations. I have been keeping 2, 3, 4, and 6 connector versions of these in my inventory of useful parts. These connectors use 3 parts to accomplish the job. There is a header (the 'posts' in the upper right of the photo), a terminal housing (the part on the right), and a crimp terminal (the part near the bottom). Using a crimping tool, the crimp terminal is attached to a wire. Then, each crimp terminal is inserted into the terminal housing. There is a small locking tab on the terminal that should prevent it from pulling free.
If you look in the catalogs, you will find that there are several variations on this KK series connector. The electrical parts are available in tin or gold. The headers are available in straight or right angles, with or without the locking ramp. I suggest getting the parts with the locking ramp. They hold the connector together better.
The terminal housing can be purchased with or without the polarizing ribs (the small tabs at the bottom of the terminal housing). I strongly suggest using the tabs. They prevent you from connecting your circuits backwards.
There are several different parts here, so I am not going to list the pricing. Mouser has good pricing, as does Digi-Key.
Yes, indeed, there really is a reason for Radio Shack to exist! :-) My favorite place to shop for breadboards turns out to be Radio Shack. Now that Karl Lunt has moved a little farther north, I am actually able to find these in stock at most of the stores in my area. They have a wide assortment of these boards in different sizes. I like the 276-149A version of the board. It has copper pads on one side only, but it is very useful for putting small circuits together. I believe this board costs about $1.39 in the Seattle area. They have smaller and larger boards as well. I actually like to keep 5 of these in my inventory. Next time you are at Radio Shack, have a look.
I like to keep a supply of battery holders on hand. I usually keep a couple of 4 cell "AA" holders, and at least 1 or 2 each of the 4 cell "C" holders. As you can see from the picture, I also have a variety of others. These are relatively inexpensive, and if you need battery power, are a must have. I also have a bag of 9 volt battery clips as well. This is another part that is readily available at most Radio Shack stores.
4 "C" cell battery holders:
|Supplier||Part Number||Pricing 1/10/100|
|Radio Shack||Various||$0.99 - $2.99|
Resistors are certainly one of the most common parts found in electronics. They come in all shapes and sizes. I have a fairly large supply of them, as will most hobbiests. If you haven't done so yet, I would suggest a trip to Radio Shack to purchase their 500 resistor assortment pack. I think it is around $6.00 or so, and will provide you with a fine selection of parts. In the picture above, you can see the bottom resistor is a 1/4 watt part. The top resistor is a 1/8 watt part. Notice the size difference!
Even if you get the resistor pack, there are a couple of values that I find extremely useful, and would suggest that you over stock on. Specifically, you should consider getting 10K 1/8w 5% and 330 1/8w 5% resistors.
The 10k resistor is probably the most widely used value in electronics. Most designers end up using them as pull-up and pull-down devices (See my article about basic circuits for more information about pull-up resistors). As such, many microcontroller circuits use them. All of my kits use multiple 10k resistors, so I buy them in the 1000's.
The 330 resistor is a decent choice for a current limiting resistor for use with LED's. (See my article about basic circuits for more information about current limiting resistors). In general, it should allow between 12mA and 15mA of current to flow through a typical LED in a 5 volt circuit. This is the other value that I consume quite quickly, and purchase in the 1000's.
Resistors are typically sold individually, or in packages of 200 or more. I like to order the larger packages. If you think you want more than 200, check out the 1000 part packages. They are even cheaper still.
10K 5% 1/8 watt Carbon Film Resistors
330 5% 1/8 watt Carbon Film Resistors
|Supplier||Part Number||Pricing 1/200|
Five years ago, finding parts was a serious pain in the butt. We all relied on the Digi-key and Mouser catalogs to find information on parts and as an easy and convenient place to purchase. Today its a whole different ball game. The internet is ripe with websites from almost all of the major distributors. Most distributors allow you to search for parts and will often times give you some pricing on the parts and also the quantity they have available. You can usually find data sheets, package descriptions, app notes, and other great information on the web. I highly recommend this as a first place to start.
A quick word about some of the distributors. When you contact them on the phone, their first hope is that you are a large corporation and that you are about to order 500,000 units of something. Of course, you are probably interested in buying 1-100 of something. They, as sales people, are going to try to fish out as much information about 'your company' as they can. This is one of the unfortunate leftovers of the old corporate sales style. For example, they are either going to ask for your name first, or your company name first. Its hard to tell which. I think it rude that someone would ask for your company name before your personal name. It has happened to me quite a few times. Roll with it.
Be bold, but be honest! "My name is Kevin Ross, I am an independent engineer, I am working on a prototype project, and I need some parts." Some of the big distributors are friendly to us small folk, some are not. You will be able to tell rather quickly. A couple of outfits will immediately tell you to go away or to call some other division in the company. Don't get put off if you get treated poorly at first, it seems to happen to everyone. Eventually, you will either find a helpful person, or call someone else!
I really like ordering from companies that allow me to shop entirely on their website. Its just a lot easier than having to talk to someone on the phone. You get the pricing information and inventory status on your screen, and you can take your time ordering.
Here is a list of the websites I use most often. I have placed these in the order that I usually use them, most often first, less often last. I have also included some comments. I would recommend any of these.
|www.digikey.com||Digi-Key||Digi-Key has been providing mail order parts for a very long time. They have an excellent reputation, a well stocked inventory, and really cater to the individual customers like you and I. Digi-Key and Mouser get about 80% of my business, and I highly recommend you get their catalog. Pricing is ok, but not great. Their website works really well, which is why I like using them. You can order online, and also track shipments online.|
|www.mouser.com||Mouser Electronics||Mouser has also been providing mail order parts for a long time. Again, excellent reputation, a well stocked and complimentary inventory to Digi-Key. Their pricing is often times a little better than Digi-Key, especially on small descrete components like capacitors and resistors. Their website is decent and workable, allowing you to order online. Mouser has several warehouses, so sometimes your order shows up in two or three boxes, which makes shipping a little higher. However, they have really good customer service.|
|www.arrow.com||Arrow Electronics||Arrow is a large distributor who seems to be pretty nice to the small guys. They do NOT have a catalog, which makes purchasing quite a bit of work at times. They have a rather extensive product line, but you have to know the part number you are after in order to find it. Their website allows you to search for parts, but often times you have to call to find out product status. Pricing at Arrow is really good. If you need a lot of one particular part, this is a great place to go. I order capacitors in the 1000's for cheap. However, there is quite a bit of time overhead required for ordering. Arrow is also small guy friendly on the phone.|
|www.allied.avnet.com||Allied Electronics||Allied is another great place to find parts. They have a fantastic catalog that is worth getting. Their website is developing nicely, but is a little clunky at times. You can order online. They have great pricing, but have a minimum order size. Allied is small guy friendly, even over the phone.|
One last thing to remember: Lead times. If you call a distributor, they may or may not tell you how long it will take to ship your part. You should be sure to take the lead and ASK: "When will that ship?". I have been burned many times on this, such as an order for a tube of 68HC811's that took 31 weeks to arrive.
If I were going to pick one of these companies as my prime distributor, it would have to be Digi-Key. They are setup to serve smaller orders with no hassles.
One quick side note: If you are shopping based on price, you need to be careful with your shipping costs. Often times, splitting an order across two companies doesn't pay. Sometimes it does pay. You need to figure that out.
For example, if you need 100 capacitors, 200 resistors, 10 microcontrollers, you might find that the 100 capacitors and 200 resistors are cheaper by $5.00 at Mouser, while the microcontrollers are only at Digi-Key. However, it is going to cost $6.00 to ship from mouser PLUS the $6.00 to ship from Digi-Key. You could combine the orders and save yourself a buck worth of shipping, even though the parts cost more at Digi-Key.
By the same example, however, a 20mhz crystal at Mouser is $0.63 and $1.30 at Digikey. Since I order in the hundreds, the price difference of $67.00 makes splitting the order a great idea!
Having a common stock of parts is a great idea if you are planning on being an active builder. A $100 investment in some commonly used parts can end up increasing your productivity and enjoyment of building projects. Careful selection of vendors can also save you quite a bit of time and effort, as well as save you money.