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Society for Amateur Scientists

Researching Electronics Information on the Web

by Paul Vito

There are several tools you should have on hand when designing building and troubleshooting electronics circuits. Some tools are obvious, but two essential tools that are often overlooked are the lab notebook and datasheets for the active components of the circuit you are working on. I don’t think I need to lecture SAS members on the importance of a lab notebook, but datasheets may not be so obvious. A datasheet contains basic information about the use and the typical performance of a particular semiconductor device. In addition to datasheets, there are other sources of information that can make development much easier, like application notes (aka app notes). App Notes contain more detailed information about typical uses of a device.

Back in the "old days" datasheets and related information were only available from OEMs and their distributors in print form. Databooks were released every couple years with a company’s complete line of products. These days it is much more cost effective to distribute information electronically on the Internet, and this is a boon for the individual experimenter. Unfortunately this information can be hard to locate as individual companies organize their information in various, sometimes cryptic, ways.

Due to the fluid nature of the Web, I will refrain from giving specific URLs (unless I’m confident of their longevity) and focus on general research techniques, something along the lines of "…teach a man to fish and you feed him for a lifetime." Manufacturers often reorganize their websites for various reasons and it is usually necessary to do some "poking around" to find the information you are looking for.

When I’m building a project I will go through the parts list and identify the active components that I am not familiar with. I then identify the manufacturers of the various components. If the manufacturer isn’t identified on the parts list, then this can be tricky. Semiconductor manufacturers tend to choose unique part numbers and prefixes for their new products, but this isn’t always the case.

For example, Analog Devices usually uses AD as a prefix for their part numbers. National Semiconductor uses LM (for their analog parts) and Maxim uses MAX. There are no hard, fast rules though, and it will take experience to learn to identify part number easily. Devices that have been in production long enough to be second-sourced may or may not be renumbered. For example, practically every analog semiconductor manufacturer makes the venerable general use op-amp, the LM741, under the same part number. National, Fairchild, Motorola, Samsung all refer to the same amp as the LM741. The classic RS232 transceiver, originally released by Maxim as the MAX232, is made by several other manufacturers under different part numbers. National calls it the DS14C232, while Analog Devices has designated the same device as the AD232, but Texas Instruments calls it the MAX232. Since these products are intended to be direct replacements for one another, you may be able to use one datasheet for another, but be aware some parameters may be different. It’s best to have the correct datasheet, if possible.

I will most often start looking for information at a manufacturer’s website. This is not always the best place to find what you are looking for, as I’ll explain below, but it is usually the best starting point. Generally the company’s homepage will have a search box. The key here, and this applies to all web searches, is to be specific without being too specific. I have found most search engines to be very inadequate, so you may have to try several variations of a part number before you get results. Some search engines don’t allow wildcards, which can make your search exceptionally painful. I begin by entering the numeric portion of the part number first. If this returns too many results, I will add the prefix of the part, and try again. If there are no results I try just the prefix and see what turns up. Depending on the results I will try removing the last couple digits. If the search engine doesn’t allow wildcards then your best bet is to enter the entire number including any suffixes. It will take some playing to find the best combination, and different manufacturers use different search engines.

If all attempts at searching on the manufacturer’s website fail (this is usually the case with "legacy" parts which the manufacturer still makes, but no longer supports), you will have to browse to find your information. In order to do this you have to understand the manufacturer’s product tree. This will require wandering around product folders, but it should take too long to find what you need. For example, if you are researching an operational amplifier you would go to the top of the product tree, a choose their "linear" or "analog" product line. From there you may have choices like "high speed amplifiers" or "low voltage amplifiers". This is where "poking around" comes in to play. There will be cases were it is not possible to browse to the information you are looking for. If this appears to be the case, you’ll need to look externally.

When searching for datasheets out on the web in general, I start with a general search engine (my personal favorite is www.google.com) and simply enter the part number. You may get lots of hits for vendors selling the parts, and there may be a link from the vendor’s page to the datasheet. Occasionally I get a hit for a link that is on the manufacturer’s website that did not show up on their own internal search engine. I still don’t understand why this is, but it’s a frustration I’ve learned to deal with.

A general search will often return hits that are associated with a project posted on the web. Often there is information that is useful to your own project, but just make sure any cached datasheets are current for your particular part, I’ve come across outdated information from time to time.

Here is an example of researching a datasheet. I had come across a Digital Signal Processor (DSP) evaluation board in a bargain bin at a swap meet. The main device on the board was a Analog Devices ADSP2181. I started at the Analog Devices home page (www.analog.com) and simply entered the part number. I got some hits but they were just press releases referring to the device when it was first released, but no datasheet. I searched for just "ADSP" and rewarded with a page full of parts with that prefix. Scrolling down I found the ADSP-2181. Apparently the hyphen was significant enough that it didn’t show up on my original search. I followed the link to the product folder where there were links to various related documents. I downloaded the datasheet and bookmarked the site for later reference. After I found the datasheet, I did a search on Google and received many hits for this particular evaluation board. Apparently it has a bit of a following out on the Net.

Now that you have a datasheet for all the devices in your circuit, what exactly do you do with it? Stay tuned and we’ll cover datasheet fundamentals in the next column…

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