Actually, that was a link to Carl's site embedded in the earlier post(s) I was responding to. I can point you to a picture of my magnet/coil sensor within my ancient article on Larry's site: http://www.seismicnet.com/leiper/Image1.gif , or you can read the whole article on that system at: http://www.seismicnet.com/leiper/seismograph.html The only difference with the current scheme is that the coil is used for feedback instead of detection, and there is a little oscillator box with a capacitor plate on the side that sits to the left of the magnet core in the plan (overhead) view with a gap of about .050". That 250 Khz oscillator is phase locked to a 1 Mhz oven crystal oscillator standard by running the outputs of each into a divide by 512 and divide by 2048 resettable counter strings respectively. This results in a "sample" rate of about 500 samples per second (488 actually). Whichever counter reaches the maximum/minimum first either increments or decrements a 16 bit counter feeding a 16 bit D/A chip whose analog output (via some tailoring circuitry) drives the coil...thus moving the magnet and changing the capacitance gap and frequency of the variable oscillator. The only "response" adjustment is how you apply the digital counter error. The way the counter scheme works is kind of like a race between the two oscillators. Both counters are reset, and begin counting (actually "down") from their maximum. Whichever one gets to "zero" first begins clocking the A/D counter (up or down depending on which counter is the "winner") until the other counter reaches minimum. I have experimented with several increment/decrement schemes. The first was to simply increment or decrement by one count and immediatley reset both counters (regardless the actual difference) because the "sample" rate was sufficiently high to "move" my first ( 8 bit) A/D quickly enough to get good feedback response. Later (here comes the fanaticism) I switched to a 16 bit A/D and counter/driver and began to clock them with the "difference count" between the two counters reaching their minimums. When the first oscillator reaches minimum it gates increments or decrements (from any of the counter/divider outputs I choose) to the A/D counter until the other counter reaches minimum...at which time both counters are reset. This allows the increment rates and decrement rates to be independently adjusted if necessary. This will be especially useful for my next version of this experiment, which will utilize two "opposed" VFOs and get rid of the Lab standard oscillator. This will eliminate the temperature drift in the VFO (relative to the Standard) since both VFOs will be affected similarly by such changes. Overall, it is an extremely sensitive method of detection that shows great promise, but there are a few more things to do... Tom On Fri, 25 May 2001 13:05:19 -0500 "Bryan&Regina Goss"writes: Thomas, Do you have any pictures of your sensor. the link you sent is Actually, that was a link to Carl's site embedded in the earlierpost(s) I was responding to. I can point you to a picture ofmy magnet/coil sensor within my ancient article on Larry'ssite: http://www.seismicnet.= com/leiper/Image1.gif ,=20 or youcan read the whole article on that system at:The only difference with the current scheme is that the coilis used for feedback instead of detection, and there is alittle oscillator box with a capacitor plate on the side thatsits to the left of the magnet core in the plan (overhead)view with a gap of about .050". That 250 Khz oscillatoris phase locked to a 1 Mhz oven crystal oscillator standardby running the outputs of each into a divide by 512 anddivide by 2048 resettable counter strings respectively.This results in a "sample" rate of about 500 samples persecond (488 actually). Whichever counter reaches themaximum/minimum first either increments or decrementsa 16 bit counter feeding a 16 bit D/A chip whose analogoutput (via some tailoring circuitry) drives the coil...thusmoving the magnet and changing the capacitance gap andfrequency of the variable oscillator.The only "response" adjustment is how you apply thedigital counter error. The way the counter scheme worksis kind of like a race between the two oscillators. Both countersare reset, and begin counting (actually "down") from theirmaximum. Whichever one gets to "zero" first begins clockingthe A/D counter (up or down depending on which counteris the "winner") until the other counter reaches minimum.I have experimented with several increment/decrement schemes.The first was to simply increment or decrement by one countand immediatley reset both counters (regardless the actualdifference) because the "sample" rate was sufficiently highto "move" my first ( 8 bit) A/D quickly enough to get goodfeedback response. Later (here comes the fanaticism) I switchedto a 16 bit A/D and counter/driver and began to clock themwith the "difference count" between the two counters reachingtheir minimums. When the first oscillator reaches minimumit gates increments or decrements (from any of the=20 counter/divideroutputs I choose) to the A/D counter until the other counterreaches minimum...at which time both counters are reset. Thisallows the increment rates and decrement rates to be independently= DIV>adjusted if necessary. This will be especially useful for my nextversion of this experiment, which will utilize two "opposed" VFOsand get rid of the Lab standard oscillator. This will=20 eliminatethe temperature drift in the VFO (relative to the Standard) sinceboth VFOs will be affected similarly by such changes.Overall, it is an extremely sensitive method of detection thatshows great promise, but there are a few more things to do...TomOn Fri, 25 May 2001 13:05:19 -0500 "Bryan&Regina Goss" <bgoss@..................>=20 writes:=Thomas, Do you have any = pictures of=20 your sensor. the link you sent is broke.[ Top ] [ Back ] [ Home Page ] Larry Cochrane <cochrane@..............>