标签: component

Several weeks ago, I was walking around my office building when I ran across my chums Ivan and Darryl playing with a new toy that Darryl had picked up on eBay.   This little rascal (the toy, not Darryl) turned out to be a component tester. I have to say that I was pretty amazed by what I saw; so much so, in fact, that I raced back to my office to purchase one of my very own.   First, I placed an order for the model Darryl and Ivan were playing with -- a Mega328 ESR Transistor Resistor Diode Capacitor Mosfet Tester w/ Test hook -- which is a mega-bargain at only $15.98 USD ($0 shipping and handling):   Mega328 ESR Transistor Resistor Diode Capacitor Mosfet Tester w/ Test hook (Source: Max Maxfield)   It turns out that there are a bunch of these things. For example, while I was rooting around on eBay, I also ran across this All-in-1 Component Tester Transistor Diode Capacitance ESR Meter Inductance (they really could work on the naming of these little scamps) for only $19.33 USD (again, $0 shipping and handling).   All-in-1 Component Tester Transistor Diode Capacitance ESR Meter Inductance (Source: Max Maxfield)   It does take a couple of weeks for these little ragamuffins to wend their way from China, but I really wasn't in too much of a hurry. They both arrived a few days ago and I just now found a few minutes to take them for a spin.   A few thought off the top of my head are that the $15.98 unit is incredibly reasonably priced and I do like the fact that it comes with the three flying test leads. On the down-side, it was poorly packed, the display was loose, and it doesn’t have an "Off" button, which means that after you've pressed the "Test" button and seen the results, you have to wait for it to turn itself off automatically.   By comparison, the $19.33 unit is more "rugged" and was much better packed. It also has an "Off" button, which is jolly useful if you want to test a bunch of components. This unit didn't come with any test leads, but overall I have to say that it's my favorite.   Next, I gathered a few components together -- a resistor, a couple of capacitors, a FET, and a relay (inductor) -- whatever I found lying around, really. Both of the units come with ZIF (zero insertion force) sockets. You plug the leads from your component into the ZIF socket (it doesn’t seem to matter which pins go in which holes), close the socket, press the "Test" button, and observe the results on the display. The image below shows the test of a 10µF ceramic capacitor.   Testing a 10µF ceramic capacitor (Source: Max Maxfield)   To be honest, these testers would be worth the money if all they did was test capacitors. I can’t tell you how many of these components I have lying around that I couldn’t use (until now) because I couldn’t read their markings. The fact that these testers also work with resistors and inductors and diodes and transistors is just cream in the cake, as far as I'm concerned.   Check out this video showing the $19.33 unit in action:   One thing that did impress me is the fact that, when I tested my FET, it appears (from the diagram presented on the display) that the tester correctly identified the fact that there's an internal protection diode. I know there is such a diode because that was one of my selection criteria when I purchased these transistors (I'm going to use them to control the meters in my Inamorata Prognostication Engine and the relays in my Nixie Tube Clock, so I need to protect myself from the effects of back-EMF).   On the other hand, it may be that this diode is just part of the FET diagram they used -- I need to try this with a FET I know not to have this diode to make sure.   The only area I think these testers could use some work is the way in which they number the component pins on the display and associate these numbers with the pins in the ZIF socket -- sometimes the mapping is obvious; other times less so -- but overall I feel this is a minor niggle and I think either of these units would complement anyone's workspace and/or make a perfect gift.

All engineers must have had the unfortunate experience of verifying a part's availability with a vendor, only to have the part ultimately wind up either not getting produced or unexpectedly canceled.   Enter an engineer I once worked with who had a serious knack for choosing seemingly phantom components that never made it to the final design. In fact, he had such an extensive track record for doing this that we called him “Mr. VVI” behind his back: for Vanished Vendor Item.   Mr. VVI gave every other engineer in the department grief for being “a dinosaur.” In his mind, the fact that we all used components that were tried and true meant that we were highly unimaginative engineers who always played it safe. As far we he was concerned, we might as well have been living in the La Brea tar pit.   We stood by, quietly gleeful as he racked up thousands of dollars in redesigns to compensate for his vanished vendor items in project after project.   There was a lot of competition in the late 1980s among AMD, IDT, Cypress, and other semiconductor companies to develop the fastest FIFO. Naturally, Mr. VVI just had to use the fastest one advertised, which, as I recall was 25 nanoseconds read time. The rest of us got by with a relatively sluggish 50 ns.   Since Mr. VVI had received actual sample devices, he decided to put sockets on his board (he would need them!). He had his circuit card populated and proceeded with testing.   Although all of the control signals seemed correct, he was not able to get any output from the FIFO. There wasn't much sympathy among the ranks, I can tell you that.   After a couple of weeks, he took the chip over to the reliability lab. They popped the cover off the chip and discovered that there was no die inside!   In the two months since he had received the samples and subsequently discovered the empty chips, the manufacturer was able to get the chips to work in functional units. So Mr. VVI got a “mulligan.”   Dwight Bues graduated from Georgia Tech with a BSEE in computer engineering. He has worked in power generation, communications, RF, command/control, and test systems for 30+ years. He is a Certified Scrum Master and teaches courses in architecture, requirements, and IVVT.

This may come out as a little off-topic, but while I was driving into work this morning, I was ruminating over a certain circuit configuration, which triggered memories of some unusual things I've run across over the years. In the early 1980s, I was working for a small company in the UK. A couple of the guys were working on a hardware accelerator project. This was a box that would be connected to a standard UNIX computer and would be used to offload and accelerate certain compute-intensive applications. I was only peripherally involved in this project, but I do recall pouring over the schematics for some reason. (This predated logic synthesis; at that time we captured our designs as hand-drawn gate/register-level schematics.) Deep in the heart of the design, I ran across a register called the LBR, which didn't trigger any obvious associations. When I asked the team leader what LBR stood for, he replied, "London Bus Register." On further questioning, he explained that this register was used to gather data, and that this data arrived sporadically in clusters. Thus, the LBR register was so named because you can stand around waiting for a bus in London without seeing one for ages, and then a load of them will arrive at the same time.   I've seen the same sort of reasoning applied in other designs. For example, one of my jobs was to write functional test programs to verify printed circuit boards designed by other companies. All I was provided was a "known good" circuit board (which often wasn't) and a set of "known good" schematics (which often weren't). It wasn't uncommon for the schematics to correspond to an earlier or later version of the board. The point of all this is that, on one of these projects, I found a so-called Banana Register in the middle of the schematic. When I eventually came to chat to the board's creator, he explained that he had named this register based on the fact that the data "came in bunches" (from which we learn that engineers do have a sense of humour—but not a very sophisticated one).   As an aside, did you know that there is a question as to whether a banana is a fruit or a herb? In fact the best answer to this poser is "both." The thing is that a banana itself (the amusingly shaped yellow thing that you peel and eat) is undoubtedly a fruit. It contains the seeds of the plant. However, a "banana tree" is technically regarded as a herbaceous plant (or herb), not a tree, because the stem does not contain true woody tissue. Come on, you have to admit that you rarely learn nuggets of knowledge and tidbits of trivia like this on any other electronics website, do you? But we digress. Over the years, have you run across any strangely named circuit elements like London Bus Registers or Banana Registers?  

During my early years in electronics, it was the heyday of lead through-hole technology. I used to love all the colours associated with various components, such as the coloured bands on the resistors shown below.   It wrote in a September blog post : "When I'm building a circuit, if I have a selection of capacitors (for example) of the required type and the same value but of different shapes, sizes, and colours, then I will select the one that best matches, complements, or contrasts the other components on the board." Of course, quite apart from their aesthetic qualities, the coloured bands on the resistors served to distinguish their values, tolerances, and so forth. This is particularly useful when you are a hobbyist, because you are constantly hunting for parts in your component treasure chest. I understand that some people think it's less important in a full-scale manufacturing and production environment in which automatic machines populate the components on the boards. However, I cannot imagine a world in which lead through-hole components were all a drab grey colour without any identifying markings to distinguish one from the other. Apart from the blandness of it all, can you conceive how difficult it would be to troubleshoot such a board? All of which leads me to an email I just received from my chum, Rick Curl: Hi Max, last month I received a bunch of circuit boards that Whitesburg Electronics assembled for me and I was surprised to see that some of the 1206 resistors had no markings on them. We have used Yageo brand resistors (that we purchase through Digi-Key) for several years and have not changed the part numbers that we order. I called Digi-Key about this. They said it was obviously a manufacturing defect and to throw any remaining parts away and they replaced our remaining stock with resistors having proper markings. Last week I received a new shipment of resistors—about half had no markings. A little searching on the Internet turned up this troubling press release . I spoke with the people at Digi-Key and this was news to them. I have always wondered why most surface mount ceramic capacitors were not marked. I would gladly pay double to get capacitors with markings on them. I hope we're not about to see resistors go the same route. Have you heard anything about other manufacturers removing the markings from surface mount resistors? It really makes it tough to do a proper visual inspection of the board. And what about Yageo's justification for this move? Environmental protection? Sounds like a smoke screen to me. Will IC's be next?   I emailed Curl to ask him about my thought that some people think it's less important to have component markings in a full-scale manufacturing and production environment in which automatic machines populate the components on the boards. He replied: We are a small company and we have third parties assemble boards for us. Not having markings makes visual inspection very difficult. Troubleshooting bad boards becomes much more difficult because, over time, there may be component value changes, and we will no longer be able to look at a resistor to verify its value. With regard to Yageo's justification of "environmental protection," it would be wonderful if manufacturers did such things voluntarily. If I were a more cynical man, however, I might be tempted to think this was more of a cost-cutting exercise. The strange thing to me is that, as big as Digi-Key is and as many Yageo parts as it carries, it is hard to believe that the company was blindsided by this. The fact that it assumed the unmarked parts were defective speaks volume. It's also interesting that Yageo didn't modify the part number when it made this change. And another strange thing is that the specification sheet for these parts on Yageo's website still indicates that they are marked. If a bunch of Yageo customers expressed their concern, it might be possible to nip this in the bud. What do you think about the idea of unmarked surface mount parts?  

Sometimes a designer himself could decide on the particular component needed without too much opposition from the Component Engineering group—often because there was no such group. But, any corporation that includes a department of component police makes a designer's job that much more difficult. Here's why. These people have the justifiable responsibility of making sure the corporate inventory doesn't get overwhelmed by several variations of the same part, when in reality, only one type is needed. They also want to ensure that the designer's choices will be available for the life of the product, are not over-priced, and have multiple sources. Sometimes, though, they go a bit overboard in their zeal and may not always understand the components or the reasons for a choice. Take a simple resistor—one company's NPI (New Product Introduction) group insisted that there were really only a handful of necessary resistor values. Its component engineer (a purely digital type) was looking at those resistors as logic pull-up or pull-down. I had to explain that you can't always make a voltage divider out of 1kΩ and 10kΩ resistors, and yes, there was a good reason for the required 1 per cent tolerance. Same for capacitors: Sometimes the company standard Y5P dielectric 0.1µF logic decoupling cap is not suitable for analogue circuits.   I remember an incident where a colleague had designed in an octal latch—I think it was a 74LS373—and on going over the timing analysis, I realised that the 20nsec data hold time would be a problem. The component cop continued to allow usage of the LS family because it was so ubiquitous and unlikely to go obsolete, but balked when I told him I wanted to use the ALS family in this particular function because of its much shorter hold time.   He was of the opinion that ALS was a passing fad, so I then told him I was going to use the F373 instead. He wanted to know why I wanted to use the F family, I told him simply "Because you won't let me use ALS." He finally agreed that maybe the LS device was not suitable and agreed to the F version. One of my engineering colleagues actually tried to specify IC sockets on his BOM (bill of materials) to prevent the cops from squelching his design choices, figuring that once the PCB was a done deal, there wasn't much that they could do. Of course, he wasn't successful in this attempt to put one over on them. Preferred vendors can be a problem. The purchasing people have their favourites, and the engineer may not always get the desired part. I had requested some optical patch cords from a certain vendor; purchasing went with a different vendor who had supplied copper cables in the past. One of the fibre cables still had the unpolished end fibre sticking out of the connector—so much for quality control. A similar quality problem occurred when I specified a certain brand of twisted-pair cable for a production test fixture. My own test fixture worked nicely with the brand I chose, but production was swayed by purchasing to go with its preferred brand. There was a huge variation in attenuation between pairs in the same cable. Let the losses begin. Sometimes, you can't get parts with multiple sources, or even a second source. Trying to explain to the components group that a certain brand of optical transmitter and receiver was the only one available at a reasonable price did not stop them from whining—until they did some of their own research and determined that there really was no choice. I did see their point, especially when that same vendor made a process change that resulted in a horrendous optical overshoot in the transmitter. I had to come up with a fix that required a large value trimmer capacitor, and because the value I needed was a year lead-time (after I bought about 400 of them myself), purchasing wouldn't allow it. We ended up using a varactor diode and a trimpot instead. The most difficult component hassle was with a simple 32.768kHz crystal and the associated CD4060B CMOS oscillator/timer IC. No way were the component cops going to allow something as obsolete as the CMOS 4000 series in a new design! It took a lot of explaining that, old or not, it was not about to go obsolete and that the chip had recently been made available in a surface mount package. I was certainly not about to design in a separate crystal oscillator and counter chain.   The crystal itself was another problem. What's so hard about procuring a 32.768kHz tuning-fork crystal that is made in the billions? None, except for the fact that the corporate-preferred vendor had none in stock and there would be a twelve month lead time. I sent a "nastygram" to the entire department explaining that I could not sit around for a year and that the component police needed to find and approve a crystal now . They did. Have you ever been a component engineer? Let's hear your side of the story. Glen Chenier Engineer