标签: resistors

I have a feeling that I'm starting to lose track of the plot. Let me expound, explicate, and elucidate (don’t worry; I'm a professional).   The Inter-Integrated Circuit (I 2 C, I2C, or IIC) bus is a multi-master, multi-slave, single-ended, serial bus that is typically used for attaching lower-speed peripheral integrated circuits (ICs) to processors and microcontrollers. The great thing about this bus is that it allows you to control a bunch of I2C-enabled shields using a single pair of pins on your microcontroller.   It's no secret that pullup resistors are required somewhere on the I2C bus (one for each of the two signal lines). This is because the pins on any of the devices connected to the bus are of a type known as open collector. However, I fear that I've been lulled into a sense of complacency, because all of my recent projects have included one of Adafruit's RGB LCD I2C shields , and these little scamps already have pullup resistors on their I2C signals. Thus, I've not been obliged to add any pullup resistors of my own.   (Source: Max Maxfield/EETimes.com)   In my spare time (ha!), I'm currently hard at work on my Capaciously Cunning Chronograph project as illustrated in the photo above. Having said this, although I've spent a lot of time on this little rascal's music mode, I've only recently begun to turn my attention to its time-keeping functions. As part of this, I'm using one of Adafruit's ChronoDot Real-Time Clock (RTC) breakout boards.   This board doesn’t have any pullup resistors on its I2C pins, but I know I'll be adding other sensors in the future that will include pullup resistors. I wasn't too sure what to do in this case, so I emailed my chum Duane Benson to noodle the situation over with him, and Duane responded as follows:   Ideally, these pullup resistors should be 4.7kΩ in value, and there should be only one pair for the whole bus. In practice, however, some shields come equipped with pullup resistors pre-installed. In this case, it's common for these resistors to be 10kOmega in value, thereby ensuring that if two such shields are connected to the bus, the shared (parallel) resistance will end up being 5kΩ.   "Fair enough," I thought to myself, so I took my ChronoDot RTC breakout board, soldered it onto an Arduino prototyping shield, added a couple of 10kΩ resistors, and connected the power, ground, and signal wires. Next, I plugged the shield into an Arduino Uno and ran the example sketch that comes with the ChronoDot RTC.   Absolutely nothing happened (sad face). I mean nothing at all (really sad face). Part of the sketch says:   if (! rtc.isrunning()) { Serial.println("RTC is NOT running!"); } I scattered additional Serial.println() function calls throughout the code like confetti and determined that the system was locking up in the rtc.isrunning() function call, but why?   I've used a ChronoDot RTC before when I was performing early algorithm development for my Inamorata Prognostication Engine. Do you remember when I was trying to calculate how many days there were until the next Full Moon, and I confused the sidereal month (with a value of 27.321661 days) with the synodic month (with a value of 29.530588 days)? How we all laughed (I'm still smiling through the tears).   The point is that I know these things do work, and last time I played with one everything was easy-peasy, so what could possibly have gone wrong? First of all I performed a Google for "I2C Pullup Resistors," which led me to a rather useful I2C at the Hardware Level tutorial on SparkFun's website.   Google also introduced me to a really interesting article on The effects of varying I2C pullup resistors . This article shows the waveforms associated with a range of pullup resistor values, starting at 68kΩ, followed by 47kΩ, 33kΩ, 10kΩ, 6.8kΩ, 4.7kΩ, 3.3kΩ, 2.2kΩ, and ending at 1.5kOmega;. A few snippets that jumped out at me were as follows:   "...notice how the measured frequency approaches our desired clock frequency between 33k and 10k ohms As you can see, 4.7k yields a good looking signal with a rise time around 1 microsecond A simple formula for calculating the smallest pull-up resistor is which for a 5V system comes out to be about 1.5k ohms. The formula for calculating the largest resistor is which yields a high side value of 50k ohms   The point that really caught my eye was when the author says "...4.7k yields a good looking signal..." "Hmmm," I thought to myself, "even though he says we could go as high as 50kΩ, is there any chance that my 10KΩ resistors are messing things up?" So I strapped an additional 10kΩ resistor in parallel with each of my existing resistors. I took a deep breath, powered-up the board, and... once again... nothing happened.   Now I was really wearing my frowny face. I was seriously contemplating dispatching the butler to fetch my angry trousers. I had been looking forward to a happy time programming my time display functions, but instead I was stumped by the hardware, which is a bit embarrassing when we remind ourselves that all we're talking about here is a small breakout board and two resistors. "How complicated can this be?" I thought to myself.   Thus it was that I returned to the all-knowing Google and searched for "Problems with I2C pullup resistors." This led me to a morass of forum postings that, initially, helped me not at all. As part of this, however, I did run across a posting from a newbie who said something like: "I'm not sure what you mean by pullup. Do I connect one end of the resistor to the signal and the other end to 5V?"   "Bless his little cotton socks," I thought (with a wry smile). "Just a minute," I thought (with a bemused look). "OMG," I screamed (inside my head -- I can still hear the echoes bouncing off my skull).   Give me strength! Since the task of wiring the board was so trivial, I'd let my mind wander while I was attaching the parts and wires, pondering all the cool things I was going to do with my code. As a result, I'd connected my two 10kOmega; resistors in series with the I2C signals instead of wiring them as pullups.   There was much gnashing of teeth and rending of garb at that time, let me tell you. So I quickly pulled out the existing resistors and cobbled together the correct circuit as illustrated below (this time I used 4.7kΩ resistors, just to make sure):   (Source: Max Maxfield/EETimes.com)   As you can imagine, I was feeling pretty confident when I powered-up this new configuration. I fully anticipated that the little scamp would now work as planned. Would you believe it -- NOTHING HAPPENED! The board still hung up at the same place!   Now I was miffed, verging on peeved. If fact, one might even go so far as to say that I was approaching a state of disgruntlement. Fortunately, when I rooted around in my "bits and pieces" box, I found another ChronoDot RTC still in its package (I've got to the stage these days where I always buy two or three of everything, "just in case"). So I quickly replicated the circuit on a breadboard as illustrated below:   Ignore the LED and resistor on the right-hand side of the breadboard; they're from a separate experiment (Source: Max Maxfield/EETimes.com)   When I was poised to powered-up this time, I would have bet money that everything would be tickety-boo. I would have lost my money. On the bright side, the system didn’t simply lock up this time; instead, I was presented with the "RTC is NOT running!" message.   I was seriously beginning to think that the fates were against me. When I looked closely at my breadboard, however, I realized that I'd plugged the SCL flying lead into the wrong column. As soon as I tweaked this, everything started to function as expected, so maybe my original ChronoDot is fried (but that's a problem for another day).   I must admit that my nerves were a bit frazzled by this time. The next day, when I was chatting with Duane on the phone, I mentioned that the ChronoDot was a bit of an awkward shape, and that working with it on a standard Arduino Uno prototyping was a pain in the tuchus, as it were. The problem is only going to be compounded when I start adding other sensors, because I also want a 9DOF sensor (nine degrees of freedom boasting a triple-axis accelerometer, a triple axis gyroscope, and a triple axis magnetometer) along with a temperature barometric pressure sensor.   Duane is also interested in having a multi-sensor shield for some of his projects, so we spent a happy few minutes rooting around on the Internet. In the end, we decided that -- in addition to the ChronoDot -- we also want to use one of Adafruit's BNO055 9-DOF Absolute Orientation IMU Fusion breakout boards and one of their BMP180 Barometric Pressure + Temperature boards.   All of these boards are accessed using the I2C bus. The reason we've opted for the BNO055 flavor of 9-DOF is that its MEMs sensor package is accompanying by a Cortex-M0 microcontroller that number-crunches all of the complicated, CPU-intensive algorithms and squeezes out the "informational juice," thereby off-loading the Arduino and -- at the same time -- making our lives so much easier.   The quick-and-dirty (let's say "cheap-and-cheerful") solution is to create a simple custom shield onto which we will attach these three breakout boards. We'll also have places for two I2C pullup resistors if required. A longer term solution might be to fabricate a more sophisticated custom shield onto which the components are mounted directly, and that will work with both 3.3V and 5V microcontroller boards, but we will leave that as a project for another day.   In the meantime, do you agree with our choice of sensor breakout boards, or would you recommend other versions? Also, would you add additional sensor types? Duane will be laying out the shield this coming weekend, so we'd appreciate your feedback sooner rather than later.  

I am a young'un, being only in my early 30s. That is why I wasn't familiar with the VoltOhmyst. I have to be honest, I bought this thing purely because the name amused me. It was only $15, so even if it is only ever an interesting conversation piece, it was worth it.   The RCA VoltOhmyst wv-97A The 1953 RCA WV-97A VoltOhmyst is a meter that is considered "service-grade." This means it works well enough, but it isn't a precision instrument.   Senior!   The top two dials are fine adjustment, while the bottom two switch modes.   This unit has been used for sure. The worn face is a testament to that. Let's open this baby up!   Simple and plain construction. I like the integrated power cord storage.   ID sticker located on the inside of the case.     The internals of the unit removed from the case. You can see the calibration system here on the back.     Looking up at the bottom of the unit. A bank of resistors in wax sleeves are visible on the mode dial. The precision resistors are seen here encased in wax sleeves. These allow for you to switch between different circuits as you switch modes.   Looking downward at the top of the unit. I doubt that this battery is from 1953.   Look closely towards the centre-right of this image. There is a yellow wire that has been clipped. This combined with the newer battery being soldered in place and some random electrical tape make me believe this has been repaired at some point in the past.       Soldering iron burn on the brown wire?     Fine adjustment on one of the modes. I'd say this is an interesting piece of history to keep around. I don't know that I have enough of a use for it to bother replacing the caps so that I could fire it up. I was able to find the manual for this unit. Like most manuals of the time, it includes calibration instructions as well as a full schematic. You can download it here if you want, but it is a rather large pdf file at almost 30MB. That should help if I do decide to make any repairs! Caleb Kraft, Chief Community Editor, EE Times  

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  

In early 1975, I had a technician post at the Woods Hole Oceanographic Institution (WHOI), before starting grad school in the fall. I had taken an extra semester to get bachelor's degrees in EE and physics at MIT, and wanted a low-key position to recuperate. A friend worked in the oceanographic instrumentation department at WHOI and had just lost his technician at a critical time in the department's efforts. The department was deploying ocean current-tracking floats using acoustic signals for ranging. The floats would send out chirps at precise times. More moans than a chirp, they swept from 250Hz to 251.5Hz over 80 seconds, and were detected using auto-correlating receivers. Signals in this frequency range propagate long distances in the Sound Fixing and Ranging (SOFAR) underwater acoustic channel. Multiple listening stations would time the arrival of the tones and track the floats at ranges over 1,000km. In addition to the SOFAR floats, one big project was a portable listening station called KAREN (Keyboard and Reader Experimental Network), named after our secretary. She had bemoaned the fact that she never got to go to all the exotic places the engineers scientists did, so the least we could do was take her namesake with us. KAREN was a mix of analogue and early CMOS logic ICs, with a paper-tape reader and strip chart recorder. Everything fit into a small metal suitcase for travel. I had spent the spring assembling and testing it, so I was reasonably familiar with its inner workings, even though I hadn't designed any of the actual circuitry. To test KAREN, someone needed to go to Grand Turk, a 1 x 6-mile island 850 miles southwest of Bermuda. Grand Turk was largely defoliated in the 1700s to make it hot and dry for sea salt production. While sea salt was no longer a big seller, the hot and dry climate remained. There was a US Navy base on the north end of the island, and WHOI had a hydrophone array there. You need a security clearance to get on the base, but the usual fellow's wife was expecting a baby. Fortunately, I had worked as a tech for a defence contractor while in school and had a clearance. They loaded me up with KAREN, a freshly minted passport (my first), and a Sony Tektronix portable oscilloscope, then off I went. I was more than a bit nervous about the responsibility I had been entrusted with, but I wasn't about to admit it. I took an early flight to Grand Turk after a night at a Miami airport hotel. The terminal was quiet, and I remember the security guy running the new X-ray machine inviting me to come around and look at the innards of the 'scope. I landed at Grand Turk and got the last of the two (!) rental cars on the island—a weathered '64 Mustang convertible. I checked in at the hotel, and managed to drive on the left side of the road out to the Navy base without mishap. WHOI's listening station was on a remote corner of the base, a few yards back from the beach, in a tiny shed with an anemic air conditioner. I hooked KAREN up to the hydrophone array, but it refused to go through the start-up process. I didn't know if it had been damaged en route, or if something else was out of whack. I was scheduled to report in to WHOI. I drove back to town to call, which a process in itself. You went to the cable and wireless office and waited until it had a free line to the mainland. To save on pricey long-distance charges, the people there would call a military base in Florida, who patched the call to Otis Air Force Base on Cape Cod, who could then make a local call to WHOI. I reported my findings and we agreed to confer in four hours. I would open up the box and start chasing signals, while they poured over the design documents to see if they could guess what was going on. I drove back to the shed, fired up the 'scope and started working through the schematics, scribbling timing diagrams as I went. Nothing appeared physically damaged. I found a spot where the edge of a logic signal had shifted just enough that it wasn't getting clocked into a register correctly, probably due to the heat. The catch was: How to fix it? There were no suitable unused gates, and I had no spare logic ICs. A quick search of the shed produced a soldering iron, a few basic tools, and in the bottom of a small drawer, a handful of mixed resistors and a few diodes. With a background in analogue design, I don't recall if I had ever heard of a diode AND gate before, but I poked around and found four logic signals that could be combined to solve the timing problem. I rigged up my AND gate and everything worked perfectly! After a few tests, it was time to report back to WHOI. I returned to the cable and wireless office and waited for the call to go through. The designer had actually managed to deduce where the problem might be, and knowing what my limited resources were, had come up with the same fix! I was more than a little proud (and extremely relieved) to report that I had beaten him to it. Testing with a SOFAR float lowered off a boat in Bermuda was delayed for a few days due to weather there, so I headed back to the hotel. The bar turned out to be the local watering hole, with a cast of characters right out of a James Bond novel. I ordered a gin tonic while they cajoled me into a round of darts, and later introduced me to a game called liar's dice. But that's another story... Doug White has worked at various research labs on a wide range of analogue, RF, and microwave circuits from VLF to W-band. After being informed, "Analogue is dead," by a digital engineering professor at M.I.T., he's managed to stay employed as a dinosaur since graduating in 1978. He submitted this article as part of Frankenstein's Fix, a design contest hosted by EE Times (US).