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awright

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Everything posted by awright

  1. I have to disagree with Gazza. Since the voltage ratio rockazella inquired about is the same for both input voltages and both are below the voltage rating for the transformer, it will be fine for stepping 120 volts down to 60 volts, as Ldanielrosa said. You don't need and couldn't use a tap to do the job unless there was a 50% tap on both primary and secondary. The primary disadvantage would be excess weight due to more than the necessary amount of steel and copper in the transformer. There might also be slightly greater fixed losses due to the larger volume of steel to be magnetized, but it's been a long, long time since I studied transformers so I may be mistaken on that. If that is true, it would show up mainly in slightly greater fixed losses at low current draw. Even though you would be using the transformer at well below its power rating, you shouldn't exceed the rated secondary current because the wire gauge was selected by the designer for the design current. awright
  2. You are describing a LIGHT ORGAN. This is a device that modulates the power to one or more lights in response to audio input to the device. While the basic components of such a device are relatively simple and straightforward, I believe that your best bet for getting one up and running by Halloween is to buy a light organ kit. There are lots of them out there. Google "light organ kit," and you get more than 3 million hits. Watch out for kits that require input from an audio power amplifier. This is the most common configuration due to the primary application of such kits. Since I gather that you want the light organ to be driven from a microphone, you would need a microphone preamplifier to drive such a unit. Since you are not looking for multiple colors controlled by different portions of the spectrum, which complicates the device, pick one described as a, "single channel" kit. A single channel light organ drives only one lamp or cluster of lamps or LEDs in response to a single audio signal. Multiple channel light organs control multiple light sources of different colors from different portions of the audio spectrum. I gather that you are not looking for that type. You can get single-channel light organ kits in the $5 to $50 range. Velleman is a very good kit maker. Here's a $5.95 Velleman kit (http://store.qkits.com/moreinfo.cfm/MK103) that powers 4 red LEDs mounted on the board and has a microphone built in on the board. Looks perfect for your project if you wanted the microphone inside the pumpkin with the light source. Consider substituting ultra-bright white LEDs for the red LEDs provided with the kit. You can get the ultra-bright LEDs from Digi-Key or Mouser or possibly your local Radio Shack. You will need a power supply in the range of 8 volts to 15 volts DC. Since the kit consumes from 0.5 to 20 milliamps (depending upon the instantaneous intensity of the light), you could probably get by for a few hours on a 9 volt alkaline "transistor" battery, which would make the whole thing self-contained with no power cord. You can conserve battery power by adjusting sensitivity to avoid having the LEDs on most of the time. Have fun. awright
  3. Well, Kevin, since millions of people use wrist straps with series resistors in the belief that the resistor will protect them from injury resulting from accidental contact with line voltage while wearing the strap, can you provide a little more fact-based analysis of why the protection is not effective, or at least beneficial enough to be used? That is, do you believe that the possible currents are above injury or fatality levels, or what? What alternative do you suggest for static protection? By the way, I'm not clear that we are talking about the same hazard when you say, "A wrist strap will not protect anybody from the AC outlet." The WRIST STRAP is not intended to protect the wearer from the AC outlet. The wrist strap is only to protect static sensitive euipment you are working on from discharge of the static electricity buildup on the body by continuously draining off the charge to ground. The RESISTOR in the lead to the wrist strap is to limit currents that could flow through the body in case of accidental contact with the line to low enough values that injury or death is avoided. Please explain why this is not protective. Please don't be insulted about this effort at clarification. You never know what experience level you are communicating with out there in the forums. Thanks. awright
  4. The second transformer will either saturate immediately or will not saturate. It is a magnetic, not a thermal phenomenon. It may overheat, also, depending upon loading and possible saturation. Well designed transformers applied within their ratings are among the most efficient items of electrical equipment. Assuming they are well designed and are used within their ratings, you can probably assume something like 95% efficiency. That is, output power will be about 95% of input power. Of course, things get worse when you draw output current in surges, as with a capacitor-input filter with large capacitors, or when you draw large output currents because more power goes into heat due to (I^2)R losses in the copper windings and the resistance of the copper increases with increasing temperature. What is your application, or are you just trying to understand transformer theory? By the way, yes, if you used one of your transformers to feed the second, and if there was no saturation of the second, and you were drawing no current, the output voltage would be 6 times the input voltage. Input/output current ratio would be the inverse of the input/output voltage ratio except that you have an additional "magnetizing current" at the input that is independent of the load current. This is the current you measure at the input of a transformer with no load on the secondary. awright
  5. Oh. Thanks for the info. awright
  6. But, Audioguru, isn't the pre-emphasis just a simple RC network that could easily be added to the Veronica? awright
  7. Well, the link opened for me, but the schematic there is impossible to read unexpanded and if you expand it you can only see a small portion of the schematic, making it difficult to read
  8. microzone, an opto-interrupter is simply a matched pair of light emitter and detector facing each other in a plastic molding that provides a slot through which an opaque object can pass to block or "interrupt" the light path from emitter to detector. Just think of it as a matched pair emitter and detector that the manufacturer has mounted for you to make it unnecessary for you to provide the optimum mounting arrangement to detect objects passing between the pair. Go to www.digikey.com and search for "optical sensors, then "interrupters." Or go to www.mouser.com and search "photo-interrupter." You could also probably use a reflective sensor which has the emitter and detector side-by-side "looking" in the same direction, away from the module. This configuration detects a reflective object passing in front of the module. However, if you can use it, I think the interrupter type would offer more reliable sensing because it does not rely on the reflectivity of the object, just its opacity, while the reflective sensor depends upon the location and reflectivity of the object being detected. These devices come in a great variety of wavelengths and physical and electronic configurations from simple bare-bones units with emitter and detector leads hanging out to amplified units, photo-darlingtons, photo-SCRs, photo-Triacs, etc., etc. Start out by finding a unit that looks like it fulfils your physical requirements then download the data sheets and application notes and see how they work and how to wire them up. You haven't given us any info on which to base a recommendation of a vibrator, but go to www.allelectronics.com and search "DCM." DCM is their prefix for DC Motor-xxx part numbers in their catalog. (All Electronics is a surplus store in the Los Angeles area.) They list several tiny vibrator motors intended for use inside pagers and phones, just the types of vibrators you would obtain by disemboweling a phone as suggested by Tedyp. These are simply small DC motors with eccentric weights on their shafts. If you need more vibratory power than these tiny devices provide (as I suspect you will if you are trying to shake a mechanism rather than a shirt pocket), you can "roll your own" by buying a larger motor and a gear or pulley that fits the shaft and sawing off part of the gear to create an eccentric weight. Try also www.candhsales.com, another surplus store, this one located in Pasadena. They have lots of motors, gears, and pulleys. The amount of "shake" you can generate by this means is limited only by the size of motor you buy and the eccentric mass. Have fun. awright
  9. Glad to see young people developing an interest in electronics, Sarah. Hope it's not too late for a few suggestions. You have probably seen the novelty caps with a small solar cell powering a fan blowing air into the cap. Consider using a small, low power motors like that with beaters or flails of various sizes and styles beating on metal or plastic sheets, pans, cups, etc., to get various sounds. Some Mallory Sonalert alarm sirens operate on very low voltage and current. They come in a variety of steady and warbled tones. Check out Mallory Sonalert, Projects Unlimited Sirens, Murata Piezo Alarms at www.mouser.com. If you can drive a mechanical buzzer with your solar cells, you can drive some of the lower power versions of these piezo alarms. You can also build very simple, very low power oscillator circuits with CMOS gate arrays or with CMOS 555 timers and drive speakers or piezo sounders. Have fun. awright
  10. Why do you say the resistor in the wrist strap will not protect you "one iota" around "high voltage"? How high is the voltage you are working around? Assuming the strap has a typical resistor of at least, say, one megohm, current would be limited to a couple of hundred microamps if you accidentally contacted line voltage. Since it is normally thought that it takes a few milliamps to cause fibrillation of the heart, wouldn't you be reasonably protected from serious shock by the resistor? If you are dealing with kilovolts, then you may have a point, but then you should be using all sorts of other precautions and static discharge is probably not an issue. While I have plenty of suspicions about the motivations of product manufacturers, the resistor in a wrist strap makes very good sense to me for all normal situations. I think selling wrist straps without resistors would be highly irresponsible. awright
  11. 77710, the voltage doubler is built into the oven circuit, as shown in the schematic you posted along with the picture of the transformer.
  12. As Tedyp said, you don't have to limit yourself to IR if the interior of the coin drop area is adequately shielded from exterior light, although IR would work fine. Do you have to detect coins of many sizes, or just one size? If one size, then a simple opto-interrupter module should work fine. If many sizes, the opto-interrupter could still work if you can guide the coins of all sizes to pass between the emmitter and detector arms, which ought to be easy. If you can use an opto-interrupter, you have very many choices of models, wavelengths, and configurations and many makers can provide application notes for their products. With an opto-interrupter, the emitter and detector are automatically matched and aligned, which simplifies the design. Also, unless the opto-interrupter is very brightly illuminated with stray light, it will probably not be bothered by ambient light because the emitter and detector are optimally oriented toward each other and are somewhat shielded by the post supporting the opposing device. Almost any small motor with an eccentric weight on the shaft should do the trick. Without knowing something about how heavy an assembly the motor must shake it is not possible to give a specific recommendation. But a little experimentation with smaller and larger motors designed to be powered with whatever voltage you have available in your machine should do the trick. awright
  13. Why would you want to reduce the temperature of the coil? Isn't it there with the intention that it get hot to aid in ingition of the charge in the engine? Are you getting preignition or some other malfunction related to the temperature of the coil? And no, there is no electrical heat sucker that can be applied to the ends of the coil. Conceivably you could heat sink the ends of the coil to the engine cylinder head, but that is a pretty inefficient path for the heat to take to reach the sink. IR emitters have to radiate their energy to lower temperature IR receivers. I suppose that, if the walls of the cylinder are a lot cooler than the coil, some radiative transfer could take place if you had IR emitting nickle. awright
  14. shaiqbashir, 5AH means 5 Amp-Hours, and is an indicator of the total energy capacity (NOT capacitance) of the battery, that is, the total energy that the battery can supply under specific, ideal, conditions. (Well, it's not really an ENERGY rating because the Amp-Hour rating does not take voltage into consideration, but it is a handy comparison between various battery sizes of the same voltage.)
  15. Well, the schematic is very difficult to read and I don't know the characteristics of the output line on the IR receiver, but the capacitor, in combination with the variable resistor, will slow down the response of the relay to either turning on or turning off, reducing chatter or excessive activations on spikes or noise from the receiver. awright
  16. jhimpex, the book you really, really need is, "High Speed Pulse Technology, Volume III, Capacitor Discharge Engineering," by Frank B. A. Frungel (with umlaut over the u).
  17. Video cameras inherently have near IR sensitivity but optical filters are added to suppress the IR sensitivity. I have heard of some people advising that you can remove the filter, but don't know if that is true. IR sensitive screens are available from some optical component suppliers. I think that Radio Shack sold such a screen at one time. Check their catalog. It looks like a slightly yellow piece of white plastic "paper" and after activation, it glows where the IR beam strikes it. I know nothing about its sensitivity, but I think it is recommended for aligning IR sources (near field only). Check out Thor Labs, Inc. ITEM # IRC3,5, or 7 at $110 each. They have 1.5" x 0.75" sensitive areas on 2.25" x 1.5" cards. The catalog blurb says, "...providing the user with an instant visible pattern for determining beam location and beam size." IRC3 is sensitive from 700 to 1400 nm. IRC5 is sensitive from 800 to 1700 nm. IRC7 is sensitive from 700 to 1600 nm. www.thorlabs.com. You can buy IR viewers for a few hundred dollars. Check out Edmund Optics at www.edmundoptics.com. Have fun.
  18. Hi ahto: You are lucky if you are in a wind regime providing useable winds and have space to put up a turbine. I'm jealous. The altermative energy industry has devices called, "Maximum Power Point Tracking Converters," that may help you out. I don't claim any particular knowledge of their internal design, but the main purpose is to maximize the amound of energy extracted from a wind turbine or solar array so that the maximum amount of water is pumped using an electrical well pump. If you get Home Power Magazine (and you should, if you are building a wind turbine), you can probably find suppliers in their ads. You can get all back issues on CDs. As you probably know, the power curve for a wind turbine generator at any arbitrary wind velocity or solar array at any arbitrary insolation starts at zero useful power for zero volts out (a short circuit that would probably burn out your generator) to maximum power in the mid range of voltage and current to zero power again at open circuit/maximum voltage. The peak power output point varies over voltage and current as wind velocity or insolation varies. The MPPT device is supposed to track that point and adjust the current demand to extract the largest amount of total energy over time. I do not know how it is done internally, but if you find out, let us know. So, my answer is yes, it is definitely possible, but, regrettably, no, i don't know how. As an aside, I just received the current online issue of the AWEA Newsletter (American Wind Energy Association) and it had an article analyzing the cost/benefit tradoff with increased tower height. The incremental benefit relative to cost for increased tower height is HUGE! So, whatever else you do, invest in the tallest feasible tower for your site. (The AWEA is a good group also, and while it is largely for the wind industry, each newsletter has a "Small Turbines" article of interest to individuals and home power entheusiasts. You might want to join them, also.) Please keep us posted on your progress! awright
  19. Consider building some electronics kits from one of the many kit suppliers.
  20. Google "conductivity meter," amd you will get a lot if information. Generally speaking, they use platimum plates to avoid corrosion and AC excitation of a full Wheatstone bridge to avoid the effect of plating on one electrode. awright
  21. Two ideas. 1) This is a classical application for a Predetermining Counter. Google "Predetermining Counter" and you will come up with dozens of manufacturers. This is the bulletproof approach used in industry for this type of application. You set the dials for whatever count you want. Press reset to prepare for counting. When the count reaches zero you get a contact closure or opening that controls a power relay. Many coil voltages are available to actuate each count, but line voltage would be simplest. You have to mechanically rig up a microswitch to produce a pulse for eash rotation. 2) Since you don't have to deal with a lot of differing situations and things are happening pretty slowly, a cheap and dirty method of stopping the machine at 10 counts would be to have a piece of very flexible, small diameter cable or nylon cord that winds up on the workpiece as it turns and activates a switch when the proper length of cord has been wound up on the workpiece. Perhaps not very elegant or precise, but probably more than adequate to get your desired number of twists. The cord could pull two contacts apart, pull out an insulating block holding two contacts together, pull out a conductive block maintaining conduction between two contacts, pull on the lever of an industrial limit switch, etc., etc. You would just have to be sure that any exposed voltages on contacts were safe and that there was sufficient overshoot available on the switch that damage would not be done as the machine coasted down. But, I imagine that your twisting machine doesn't do much coasting after power is cut. Your contacts would control a power relay controlling the motor. awright
  22. konrad, you indicate in your original post that you want a parabolic mic for very close range. The characteristic of a parabola is that it will focus all rays (optical or acoustic) originating at INFINITY to one point. It is a special case of an ellipse, that has two finite foci. You don't indicate the distance or frequency range that you intend to operate at, but I presume you mean high frequencies at a few inches to a few feet. If that is the case, you would be better off using an ellipsoidal reflector with the noise source at one focus and the mic at the other focus. Now, all this becomes somewhat academic, depending upon what you are trying to accomplish with your reflector, because the finite size and imperfect placement of the micropone diaphragm broadens the central lobe of the polar pattern of the reflector so the exact mathematical theory also becomes blurred. Additionally, while buying or fabricating (by spinning a bowl of epoxy at a constant speed as it hardens) a parabolic reflector is not too difficult, fabricating an ellipsoidal reflector might be a little more difficult, perhaps requiring cutting out an ellipsoidal template and using it to form a mold that you cast a reflector in. The gain/directivity of a reflector mic is directly related to the size of the reflector relative to the wavelength of the sound. I built a 1 meter diameter reflector once that worked excellently according to theory, but had almost no directivity below 1KHz. Have fun. awright
  23. madammim, as other posters have said, the transformer core has to be magnetically "reset" between cycles to avoid saturation of the core and resulting high currents limited only by the resistance of the wire in the primary winding.
  24. Hi Ann Margareth: 1 uF at 15 or 25 volts is a very common capacitor value that you should be able to find at Radio Shack, any electronic supply store, electronic surplus store, Digikey, Mouser, or on scrap circuit boards. But you can also substitute with little difficulty. No identification is shown for IC1, but it looks like a classic 555 timer application. The capacitor on pin 7 of IC1 is part of the time constant setting circuit that determines the on and off times of the output to the LED. I don't know what the capacitor and resistor values are, but you can calculate the design duty cycle and period by reference to the 555 spec sheet. Google "555" and you will find many tutorials showing how to calculate period and duty cycle for the recommended components. If you don't stray too far from the 1 uF design value you can compensate for a different value of capacitor by selecting different values of resistors in the string. Thus, if you use a 0.5 uF capacitor at IC1, double the values of the two resistors above it in the schematic. The second capacitor is not at all critical, as it is only setting a response time for the LED drivers. A larger capacitor here will make the LEDs slower to respond to the input pulses and conversely. I'd bet that you could vary the value of the second capacitor by +/- 50% without noticing any change in performance. I wouldn't try to compensate for any modest changes in the value of the second capacitor. The value of this capacitor does not have to match the value of the capacitor at IC1, since it does not have any "tuning" or frequency determining function. Have fun awright
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