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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#42
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Ping Jim Wilkins: Audio filter
On Sat, 08 Apr 2017 15:06:40 -0700, Gunner Asch
wrote: On Fri, 7 Apr 2017 13:01:13 -0400, "Jim Wilkins" wrote: wrote in message ... Yo Jim -- and anyone else who may be interested. I spend an hour last night tracking down some noises in my furnace blower, using my usual piece of aquarium hose stuck in my ear g, and I wondered if there might be a market for an advanced kind of mechanic's stethoscope -- something that ought to be a piece of cake for someone like you. Maybe something like this is on the market. If so, forget it. If not, consider this: I had two noises, from different sources, and the interference between them made it all but impossible to find the origins of the noises. One was some mechanical interference between the centrifugal fan and its housing, at one end of the armature shaft; the other was vibration resulting from stickiness in the centrifugal throw-out switch (a fail-safe switch that prevents the gas valve from opening), at the other end of the shaft. I finally took the whole thing apart and found both problems, but it wasn't easy to find them when the motor wasn't running. So, I wondered about the idea of making a small, cheap, battery-powered amplifier, with a mike and a headphone jack, that contained a couple of active, adjustable audio filters, one high-pass and another low-pass. Made a notching filter or bandpass filter to make it slick. I don't play with engines much these days, but I can recall times when such a device would have made quick work of tracking down engine noises. There it is. If you make it and sell it, the idea is yours. Watch out for patents. http://www.harborfreight.com/mechani...ope-69913.html Long screwdrivers seem to get used more often than my stethoscope. -- Newman's First Law: It is useless to put on your brakes when you're upside down. --Paul Newman |
#43
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Ping Jim Wilkins: Audio filter
On 8 Apr 2017 00:18:53 GMT, "DoN. Nichols"
wrote: So, I wondered about the idea of making a small, cheap, battery-powered amplifier, with a mike and a headphone jack, that contained a couple of active, adjustable audio filters, one high-pass and another low-pass. Made a notching filter or bandpass filter to make it slick. Instead of a microphone, use an old phono cartridge with a brass whisker where the needle normally was held. (Ceramic or Crystal cartridge -- not the fancier stereo cartridges of higher quality and lower stylus force which came later.) Astatic was the brand of one of these types. I wonder if you can still find them on eBay? I did essentially the same thing except that I used the active element out of a cheap set of headphones. In this design, the speaker "cone is a somewhat corrugated piece of clear plastic with about a 3/4" diameter "voice coil" and a super magnet. The other pole piece is a cylindrical piece that almost touches the cone. I went this route because I found phono cartridges much too fragile. I cement the rod to the center of the cone with strong but resilient (E6000) cement. If I push too hard, the cone moves until it touches the center pole piece and no damage is done. In fact that forms a mechanical high pass filter which is usually needed. In the electronics box was an amplifier, a low pass filter, a high pass filter and a bandpass filter with adjustable width. I used the unit mostly for charging AC systems where I didn't have a refrigerant weight to go by. As I described previously I listen to the refrigerant flow. The band pass filter was invaluable. It chopped all the low frequency noises such as the compressor compressing, the engine running and so on. It also chopped the high frequency of the refrigerant flowing through the rest of the system. A notch filter would have been handy, though I emulated one pretty well by drawing the high and low pass filters close together. Especially handy for listening for ball bearings that have a bad ball but aren't making noise yet. one can notch out the regular beat of the balls rolling and hear just the clunk of the one ball with a flat spot go by. When I get time I am going to re-implement this as a learning DSP project. This time with a display capable of showing an FFT so that I know where to put the band pass filter or maybe have it auto-find the peak of interest. This an ultrasonic listener are two of the more useful tools a modern mechanic can have. It sounds interesting -- and more so if you can do stereo pickups with old phono cartridges. :-) I didn't find stereo all that useful. The probe is extremely directional off the end, sensitive to longitudinal motions of the probe. One simply changes the angle of the probe to go looking for the noise source. John John DeArmond http://www.neon-john.com http://www.tnduction.com Tellico Plains, Occupied TN See website for email address |
#44
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Ping Jim Wilkins: Audio filter
On Sat, 08 Apr 2017 17:02:02 -0500, Tim Wescott
wrote: That's a bit over 11C, which is well within the limits that model airplane battery packs are run these days. Every day packs come out that can handle more current for the capacity -- it's probably tools like that which are driving it. That, EVs and grid level energy storage. I have a friend who is one of the top guns in EV drag racing. His rail dragster isn't all that much slower than Top Fuel. I have in my hands one of the batteries he developed in conjunction with a chinese battery company. It's a bit smaller than a garden tractor battery, 48 volts and 14 amp-hours. The real kicker is that it is capable of supplying 1000 amps while keeping the voltage above 46 volts and do so until the charge is depleted (defined as 20%). I'm working on a product that will use 2 of a lower capacity version of that battery (96 volts, 7 amp-hours). I have to say that I work with that little bomb with great trepidation. John John DeArmond http://www.neon-john.com http://www.tnduction.com Tellico Plains, Occupied TN See website for email address |
#45
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Ping Jim Wilkins: Audio filter
On Sat, 08 Apr 2017 21:26:25 -0700, Larry Jaques
wrote: On Sat, 08 Apr 2017 15:06:40 -0700, Gunner Asch wrote: On Fri, 7 Apr 2017 13:01:13 -0400, "Jim Wilkins" wrote: wrote in message ... Yo Jim -- and anyone else who may be interested. I spend an hour last night tracking down some noises in my furnace blower, using my usual piece of aquarium hose stuck in my ear g, and I wondered if there might be a market for an advanced kind of mechanic's stethoscope -- something that ought to be a piece of cake for someone like you. Maybe something like this is on the market. If so, forget it. If not, consider this: I had two noises, from different sources, and the interference between them made it all but impossible to find the origins of the noises. One was some mechanical interference between the centrifugal fan and its housing, at one end of the armature shaft; the other was vibration resulting from stickiness in the centrifugal throw-out switch (a fail-safe switch that prevents the gas valve from opening), at the other end of the shaft. I finally took the whole thing apart and found both problems, but it wasn't easy to find them when the motor wasn't running. So, I wondered about the idea of making a small, cheap, battery-powered amplifier, with a mike and a headphone jack, that contained a couple of active, adjustable audio filters, one high-pass and another low-pass. Made a notching filter or bandpass filter to make it slick. I don't play with engines much these days, but I can recall times when such a device would have made quick work of tracking down engine noises. There it is. If you make it and sell it, the idea is yours. Watch out for patents. http://www.harborfreight.com/mechani...ope-69913.html Long screwdrivers seem to get used more often than my stethoscope. Ayup. I keep a 18" long Klein phillips screwdriver in my Platt tool case that gets nearly all this sort of duty. Gunner --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
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