标签: amplifier

Well, things are bouncing cheerily along, as they do. With regard to my previous column about locking down the final layout for my Vetinari Clock, we've pretty much boiled things down to the two choices shown below.       In the upper image, we have our tree-switch group on top; also, the "peaks" in the black cabinet located over the big meter to the left and the switches to the right are on the same horizontal plane. By comparison, in the lower image we have our two-switch group on top and the tips of the "dips" in the black cabinet are on the same plane.   Now it's time to consider the operating modes we are going to implement along with any associated sound effects. But before we go there, I'm afraid I have to confess to having been lured to the "dark side" by the somewhat naughty project suggested in a recent Practical Joke column. Inspired by that column, I'm going to have an additional three-way toggle switch on the back of the clock. This switch will select between three super-modes: Standard Mode: This will be the switch's center position. In this case, the clock will behave according to the current sub-mode as defined by the switches on the front of the clock. Modifying the state of the switches on the front panel will simply change the current operating mode. Loki Mode: This will be the switch's up position. When this mode (which is named after the Norse god of mischief and trickery) is entered, the clock will continue to behave according to the current sub-mode as defined by the switches on the front of the clock. However, modifying the state of any of the switches on the front panel will cause the analog meters to start oscillating wildly and the LED's on top to flash enthusiastically, all accompanied by some heart-stopping sound (to be determined). Returning the three-way switch on the back of the clock to its center position will cause the clock to resume its Standard Mode operation. Test Mode: This will be the switch's lower position. In this case, the clock will perform a variety of test sequences (to be determined) as defined by the switches on the front of the clock.   All of this is going to be controlled by two Arduino Uno microcontroller development boards. One of these Arduinos will be the master in charge of orchestrating operations. This board will access data from a real-time clock (RTC), drive the meters, control the LEDs in a NeoPixel Ring mounted under the vacuum tube on top of the case, decide what sounds are to be employed, and so forth.   The second Arduino will set up as a slave on the I2C bus. This Arduino will be in charge of handling the sound effects themselves. When the master Arduino issues an appropriate I2C command requesting a particular sound, the slave Arduino will make it happen. With regard to the sounds themselves, I'm using a Wave Shield from Adafruit. This little scamp can play uncompressed 22KHz, 12-bit, mono Wave (.wav) files of any size.   But now we have to decide what modes we wish to implement and which sounds we'll use to accompany and complement these modes.   What modes? We already discussed the fact that we need some sort of sound effect for use with the Loki Mode -- when someone modifies the state of a front-panel switch, this sound will start up. Maybe we should have a number of such sounds and randomly move between them as the operator frantically manipulates the front panel switches.   With regard to the switches themselves, my original thoughts were that one of the two-switch group could be used to turn the sound on/off (except in Loki Mode, of course), while its companion could be used to enable/disable any lighting effects associated with the vacuum tube located on top of the cabinet. This would leave the three-switch group to define one of eight operating modes.   The more I contemplate and ruminate on this, however, the more I'm coming to the conclusion that the switches to enable/disable the sound and light effects can live quite happily on the back of the clock. Actually, the more I think about this, the more I think we are going to need some additional switches on the back of the clock anyway, because I'm not sure how we can achieve everything we want to achieve using only the five switches on the front.   Let me share my current thoughts with you, and then we'll see if we can decide how to accommodate things using our existing front-panel switches, along with any additional switches we can add to the back of the clock as required.   Let's start with the main modes I'm considering as follows: Standard: In this case we just need a regular "tick-tock" sound effect. Vetinari: Remember that this is our namesake mode. This is the one where the clock continues to keep perfect time overall, but the ticking of the clock follows a disconcerting rhythm, something like "tick-tock tick-tock tick... ... ... tock-tick-tock..." and so forth. Clockwork: In this case, I'm envisaging the constant sound of clockwork gears and other mechanical mechanisms beavering away in the background. The regular "tick-tock" sound would be modified to fit in with this theme. Also, there would be additional effects accompanying things like the rollovers at the end of each minute and at the end of the hour. Air and Water: In this case, the "tick-tock" sound would be replaced with the sound of water drips. Also, there would be additional background sounds of running water and pneumatic bursts of air accompanying things like the rollovers at the end of each minute and at the end of the hour.   As you see, thus far I've only come up with four main modes. Can you suggest any others? Now, although I'm considering the modes described above to be the main modes, I'm also thinking of an additional characteristic that "overlays" all of them. We might think of this as "analog versus digital." In the case of a regular analog clock, as the "big hand" moves around the clock, the "little hand" gradually progresses between adjacent hours in an analog fashion. This is one of the things that makes a regular analog clock tricky to read for younger folks.   In the case of our Arduino-based clock, we have much more control. We can certainly have an analog operating mode in which the needle on the Hours meter gradually progresses from one hour to the next. But we can also support a digital alternative in which this needle remains pointing at the current hour until the rollover at the end of the hour, at which time the needle could move directly to point at the next hour.   Another effect I want to include is something I think of as the "Straining" mode. This could be used to augment any of the four main modes, but only if we were using the digital characteristic we just discussed. Let's start with the Standard and Vetinari modes. I'm imagining that -- assuming the "Straining" mode is engaged -- when we reach the end of the hour, the needle on the "Hours" meter will start to quiver and we will hear some sort of a straining sound with tension building until... the "mechanism" releases (with an appropriate sound effect) and the needle moves to point to the next hour.   If you were here in my office, I could mimic an appropriate sound for you. As it is, you'll just have to use your imagination. Ideally, I'd also like equivalent "Straining" sound effects to accompany the Clockwork and Air and Water modes.   OK, I have a couple more supplementary modes, but I'm not quite sure how they should fit in with everything we've discussed far. What I'm talking about is to have a sort-of "Cuckoo Clock" effect, but with an amusing/strange cuckoo sound; also a sort of "Westminster Chimes" effect, but -- once again -- an unusual/amusing version on the basis that the only time I like hearing traditional versions of these chimes is when I'm standing outside a real church tower.   Actually, I think these supplementary modes could augment all of the four main modes, and they would work with both the analog and digital operating modes, but they would be dominant over (or subservient to) the Straining mode -- that is, you couldn’t have these supplementary modes and the Straining mode active at the same time.   So, before we proceed to the next page, are there any more modes you think we should implement? Also, can we map the various modes discussed above onto our five front-panel switches, or do we need to add additional switches on the back of the cabinet?   Which sounds? Based on our earlier discussions, the next step is to decide which sounds we wish to use. Originally I'd thought of synthesizing the sounds, but real-world versions sound (no pun intended) so much better. This is why I opted to use the Wave Shield as noted earlier.   So, we know we need a "tick-tock" sound. We also need a selection of sounds to accompany the Loki mode. Similarly, we're going to need suites of sounds to complement the Clockwork mode and the Air Water mode, where these suites cover both the regular running and the rollovers at the end of each minute and the end of each hour.   Then we are going to need the various "Straining" sounds to augment the four main modes. And, finally, we need additional sounds to implement our "Cuckoo Clock" and "Westminster Chimes" modes.   Now, there are a variety of websites from whence one can download free sound snippets, such as FreeSound.org . For example, consider this slow-ticking pendulum clock .   Once we've located appropriate sound snippets, we can chop out the parts we need using the free Audacity audio editor. The only problem is that there are so many options that my head is spinning. I was rather hoping that you might help out by rooting around and suggesting appropriate sound samples we could use.   What about an amplifier and speaker? The last point to consider is the audio system itself. I've not found the time to assembly the Wave Shield yet, but I'm assuming the little speaker that comes with it won’t provide the "rich and fruity" tones I desire.   I'm thinking I'll need a bigger, better speaker and a little amplifier to accompany it. The inside of the cabinet will be able to accommodate anything up to 8" in height. Sad to relate, however, I'm not an expert in the audio side of things, so I'm more than open to suggestions.   All of which leads me to ask if you have any ideas you'd care to share. How about your thoughts on mapping the modes described in this column onto the five switches on the front panel -- will we need additional switches on the back of the case? Are you bursting with inspiration regarding additional operating modes? And, last but certainly not least, any suggestions with regard to appropriate sound samples would be very welcome, as would proposals with regards to my choice of speaker and amplification.

Red Wine Audio, a battery-powered audio equipment company, displayed an unusual modular integrated amplifier at the recent New York Audio Show. No, I'm not talking about the change in brand from the usual Red Wine Audio to Vinnie Rossie (the founder). Instead of a battery, the amplifier uses ultracapacitors. Yes, you read that right! The amp has 18 ultracapacitors in two banks, reports the Stereophile magazine. The report says the capacitors were developed for use in automotive regenerative braking systems. The two banks allow for one to charge while the other is discharging—the switching, I understand from other reports, is seamlessly implemented. So what's the benefit? Really fast charging and really long battery life—rechargeable batteries offer limited charge-discharge cycles. Clever design. Oh, I almost forgot to explain how the Vinnie Rossie Lio is modular. Like many of the company's products, you can customise it with your choice of modules: a DAC-preamp, a phono preamp, an integrated amplifier, a headphone amplifier, etc. Red Wine Audio's home page at http://redwineaudio.com/ says the product will be released this month. --Vivek Nanda

It was an early autumn afternoon when I first saw her. It was my third year of engineering school, and what looked like the final year of her hell. She was propped up against some discarded trash, carelessly left in a mangled heap. Her innards were strewn about, hanging out a nasty opening in her back. I remember being dumbfounded that she was there at all... surely, someone would have noticed, called in about the mess. It seemed sick for someone to care so little about her... worse yet, I was practically salivating at this point... I had always wanted to play God. That night I gathered a trustworthy crew and an old Chevy, and we abducted her remains in the early hours of the morning. My crew helped me lug her carcass into the basement and promptly left me to my work. I grabbed my tools and carefully analysed her state of despair—tracing back her innards, determining if anything was missing. At one point in time, she was definitely a beautiful organ—a Hammond organ, or so the labels read. Now she was a hideous wreck, nothing but a scar on the face of our throwaway society. Some unskilled fool had clearly tried to service her back into health... her wires were everywhere (except where they should be, of course). Her cabinet speakers were dangling from their connecting wires. Sickening madness. Her 120V service cord had seen better days, her wiring mostly disconnected and hanging limp in her body cavity. I started my work by giving her a new power cord—ripping a replacement from a dead microwave. My beauty-to-be would be part organ and part microwave; this had me captivated. I carefully reconnected the entire wiring harness, remounted her speakers, double checked the connections, and as my heart pounded, I threw the switch. The lights came on. The hum of an open-input amplifier kicked in, gaining volume as the tubes warmed. My heart was racing as I reached down and touched middle-C, but not even a whisper. I meticulously fiddled with the tone controls, the volume pedal, anything I could to get a rise out of my monster. And yet, nothing. An empty shell of her former self. I switched her off, and returned to examining her carcass. Doubt started to set in. I checked the power connections for every sub-system: the power amplifier, the pre-amplifier, the DC power supply itself... nothing. They all seemed to work, throwing off heat and a warm orange glow from their dusty vacuum tubes. She was missing a voice—she just sat there, screaming nothing at the top of her lungs. Tracing the wires told me that the signals themselves came from a large nondescript metal box, the inside of which was absolutely packed with gears, actuators, and other mechanical-looking things. It was every bit as complex as the innards of an animal. All of this intricate metal—the bulk of my lady's weight—was ripe with grease and mechanical wear. She had certainly seen her share of players. I had her plugged in as I carefully looked over her corpse, and that's when I noticed that my girl was trying to speak to me... through all of her wreckage and despair, she had a little motor that was vibrating and throwing off heat, as it tried to start her mechanical being. To think that her little motorized heart had seized—the odds of me finding a compatible motor for my darling were slim to none. Doubt crept closer yet. While hopelessly trying to give the motor a manual start, a large metal can tucked in behind it caught my eye—could that be it? Her plagued little heart was an old AC motor, and all her suffering was at the hands of a dried-out start capacitor? I hurriedly tore a high-voltage capacitor out of that junked microwave, and crammed it in place of the old capacitor. I didn't even take the time to check values at this point—I quickly wired her up. I flicked the switch. The lights came on... my eyes widened. The hum of the amplifier began to rise over the sound of my own pounding heart. And the moment of truth I pushed my palm into her keys and out of her aching body roared the clamorous, atonal wreck of a mashed keyboard—I had done it! I had bent nature to my bidding, I had resurrected the dead... I don't know that I'd ever felt more accomplished. I excitedly poured over my new love, and we made haunting music well into the early hours of the morning. My townhouse neighbour would file many complaints. The lady and I would never care. Months had passed, perhaps a year, and my beloved and I had gotten well acquainted. We made music together in the darkness of my basement lair; I even dressed her up in modifications to hook into some guitar pedals. But, my precious was living on leased time. In fact, the lease to my building was coming to an end, and nobody in their right mind would help move my 300-pound lady up four flights of stairs to the new flat, myself included. She wasn't quite aware of it yet, but our parting was in the works. I put ads out to send her to a loving home, but nobody dared pull my beauty out of the basement I had her holed up in. The solution was clear in my mind. She had always been an entertainer—a final performance seemed appropriate. I sat and played her off into death, while friends and acquaintances destroyed her beautiful body with power tools and large, blunt objects... admittedly a savage death. We crushed my beloved into a heap of rubble, and I piled it into her dumpster grave that morning. Goodbye, my dear. You made for one hell of a party. Troy Denton is a computer engineering graduate from the University of Manitoba. When he's not working or sleeping, he's tinkering with embedded systems (and throwing the occasional workshop). He submitted this article as part of Frankenstein's Fix, a design contest hosted by EE Times (US).  

Have you wondered one thing—that how widely electronics is used? This blog gives you a small-window view of the places where electronics is used and has been sitting silently in our lives over the years. Now switch over to our health needs and how medicine and medical equipment is an inseparable part of modern life. Lifestyle diseases are very prominent among us these days. Along with it comes all the medicine and of course the use of medical equipment. Think of any of those and you will get one thing common and that is the presence of electronics in all of them. From the tiny gadget that checks the amount of sugar in blood to the bulky ECG machine which measures your heart operation. We'll try to cover one such application in this blog. Figure 1 What is this ECG ? ECG stands for electrocardiography. We all know that our heart is a muscle formed in a way that allows it to act as a pump for blood. This process is the acquisition of electrical activity of the heart captured over time by an external electrode attached to the skin. Each of the cell membranes that form the outer covering of the heart cell has an associated charge which is depolarized during every heartbeat. These appear as tiny electrical signals on the skin which can be detected and amplified by the ECG. These electrical signals are then given to an ECG pre-amplifier. We'll see one type of such an amplifier—instrumentation amplifier. Before going into it, let us see the differential amplifier. A differential amplifier amplifies the difference of the two signals given as input to it. This is very important in our application because it rejects common mode voltages while amplifying the differential signal of interest. Figure 2 The circuit shown above is of a differential amplifier. You will see that this circuit is a combination of an inverting and a non-inverting amplifier. Run the circuit and see the output is a difference of the inputs. The main advantage of this circuit is that this circuit can remove the error caused by common mode voltage. What is common mode voltage? These are signals that are common to both inputs of the opamp. Common mode voltages cause a certain error in the output of the opamp: this error is measured as the common mode rejection ratio . For example, suppose equal 60Hz noise* is present on each input and one input is at 5V dc and the other is at 2V dc . The common noise is cancelled out in the difference and the 3V difference is amplified. This circuit has some restrictions also—it being that the input impedance is limited by the resistors R2 and R3. We all know that the input impedance looking into the amplifier should be high. So if a high gain is required, then a high R0/R2 ratio is required, yet practical circuit considerations limit the maximum and minimum values for these resistors. The solution to both high-gain and high-input impedance problems is the instrumentation amplifier (INA). This circuit uses three opamps. Figure 3 Use the inverting amplifier equations to derive an equation for the gain of the first stage. The input is the difference between the two points connected to positive of opamp and the output is the difference between the two outputs of the opamps. This gain of the first stage comes to A v¬ = 2(R 1 /R 0 ) + 1. This is then given to the final stage which in itself is a differential stage. So finally the output from the circuit will take into consideration this too – thus the final gain will be . The main advantages of INA's are: ability to obtain high gain with low resistor values, extremely high input impedance, and superior rejection of common mode signals. Modern INA's are of the monolithic IC form with terminals for the R0 resistor which is usually variable and can be used to control the gain. You can see details about these ICs here:  http://www.analog.com/en/specialty-amplifiers/instrumentation-amplifiers/products/index.html#Instrumentation_Amplifiers As a conclusion it should be noted that there are more complexities involved. There will be a filter connected to this amplifier as well as an isolation amplifier involved mostly to eliminate noise. There will also be circuitry to null out a dc offset introduced by the electrodes that are connected to the patients. We will try to introduce them in the coming weeks. For now this is just an introduction to a simple bioelectric amplifier and its concept as well as its implications in ECG. Visit the following sites to try designing these circuits: http://www.docircuits.com/circuit-editor/205 http://www.docircuits.com/circuit-editor/206 * 60Hz noise is the noise introduced due to electromagnetic disturbance from other electronic appliances in the room along with the ECG machine.

The product line card of Microchip is more a telephone book than a card. Like so many other vendors they offer hundreds of variants of their processors. Many sport the same CPU but vary in memory configurations and I/O mixes. That's great news for developers who want just the right peripherals for a particular application. But their new PIC16F178X parts draw the circle around the microprocessor chip a bit broader than usual. Peripherals ( if you can call them that ) include up to three op-amps that can be "wired" by setting configuration bits in different ways, as well as up to four analogue comparators ( which are distinct from the op amps ). The downloadable PDF datasheet for the 78X is a bit weak on details. But the gain-bandwidth product has a "typical" spec of 4.3MHz, which is probably faster than one would need for use with this eight-bit CPU. Interestingly you can set one of two GBWP values, a "high" and a "low," though these levels have not been characterized yet. Open loop gain is also only given with a "typical" spec but is a 90 dB, and the slew rate is similarly rated at a respectable 3 V/uS. ( Microchip tells me these specs will be fully characterized later this year ). The inputs can go to the part's fixed voltage reference, the output of the DAC, or a pin. Outputs can go to pins and other on-board components, though the datasheet is silent on those connections. However, other material Microchip provided shows them connected to the comparators and the A/D input. An example application for a three phase motor controller is shown in Figure 1 below:   Figure 1 ( I especially like the cloud labelled "Firmware Control," as if a little hand-waving will magically generate the software! ) The cost is a little over a buck in volume, and twice that in singles. The on-board analogue is a cool idea that can reduce parts count and improve integration. Op-amps are available on other vendors' products, such as some members of the MAXQ family from Maxim, but to my knowledge this is the first time they have been so tightly integrated onto the CPU, with programmable connections allowing a wide variety of applications. ( On a related note, I came across TI's wonderful Handbook of Operational Amplifier Applications, a free 94 page .PDF available here .)