RPM Meter
in [Design]
|
Prev: Bad Omen?
Next: Posts with threaded holes
From: markp on 28 Jul 2010 14:06 "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote in message news:7fo0565v22304jmkgfs3tcbq1abu2i6f5i(a)4ax.com... > On Wed, 28 Jul 2010 16:36:00 +0100, "markp" <map.nospam(a)f2s.com> > wrote: > >>> >>> John "The Bloviator" Larkin's post is a slap-it-on-paper-quick without >>> thinking "solution". Use at your peril. He'll never label it with >>> values. If he did, his "solution" could be checked. >>> >>> ...Jim Thompson >> >>I rest my case. >> > > Ask him for values that will work in your application. > > I rest MY case :-) > > ...Jim Thompson You seem to be under the impression this newsgroup is all about real, practical solutions. It's not, sometimes ideas are just as important. Even though they may not be practical, the ideas may spark other ideas. Anyway, anyone doing a practical design which they need to work should be able to work out for themselves whether it will or not, otherwise they are blindly copying someone else's design from someone who hasn't signed a contract and is therefore can't be sued if it doean't work, and hoping for the best. Let me tell you something. You plaster your company name all over this newsgroup. What do you think a prospective new customer, or even an existing customer, of yours will make of you sniping at others so often if they read these posts? They are very likely to do some searching before commiting to doing business with a new designer, after all it can be somewhat risky, they will want to protect themselves by finding out as much as they can about you beforehand. Well here are a few things they might think. Maybe they'll think you seem to be extremely egotistical in that you want people to fully specify the problem, and complain when they don't, and for it to be you who suggest a practical impelentation. Maybe they think you are hooked on needing the praise and aclaim that it gives you. Maybe they'll think you obviously see others who post incomplete circuits or just ideas as some kind of threat, or somewhat inferior. Maybe they'll think you are unstable, that your are stressed because business is failing, that you might not be around to complete the project they want you to do. Maybe they might think you're just going senile and are frustrated that you might be losing it and that's why you need to keep proving yourself all the time. None of the above will leave them with a positive impression of someone they are thinking of doing business with. I'm not suggesting for a second that any of this is true. It actually doesn't matter whether any of those things are true, or even if they are close to the truth, it's the impression to your customers that counts. These posts remain in search engines much longer than the newsfeeds hold current threads. They appear as mirrors on web pages. Maybe one day your business needs a big customer to survive and they read this, and decide to check on all your other previous posts just to be sure, and then come to one of the above conclusions and reject you as a result. So, I have nothing against you as such, but I do think this sniping will damage your business, and you personally, if it carries on. Take a step back, do some meditation or get some therapy or do whatever you have to do, and think about the potential harm this behaviour is doing. Seriously, this will definitely be harming your business one way or the other. Mark
From: David Eather on 28 Jul 2010 19:48 On 28/07/2010 9:09 PM, Jan Panteltje wrote: > On a sunny day (Wed, 28 Jul 2010 12:08:10 +1000) it happened David Eather > <eather(a)tpg.com.au> wrote in<RuidnQS0OouWDNLRnZ2dnUVZ_t2dnZ2d(a)giganews.com>: > > >> PIC? Shouldn't you use something like a 555 and an analogue meter? > NO But a 555 is the highest example of the chip designer's art.
From: Grant on 28 Jul 2010 20:47 On Wed, 28 Jul 2010 08:41:55 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Wed, 28 Jul 2010 21:24:48 +1000, Grant <omg(a)grrr.id.au> wrote: > >>On Wed, 28 Jul 2010 01:08:54 -0500, "bw" <bwegher(a)hotmail.com> wrote: >> >>> >>>"Dookie" <abstract.dissonance(a)gmail.com> wrote in message >>>news:29566efc-1fcd-4f2f-b30a-d78cab3d7bc7(a)q35g2000yqn.googlegroups.com... >>>>I have a contact/photo rpm meter but it is acting funky and would like >>>> to create a simple meter for some testing. >>>> >>>> I've created the pic code and seem to have gotten it to work but need >>>> some sensor to debug it. The pic code basically counts the time >>>> between pulses. I do not use the ADC but rather the digital inputs and >>>> monitor when the pin goes high. The code does have built in dead time >>>> to prevent multiple countings. >>>> >>>> My idea was to stick a magnet on the device I want to measure the >>>> rpms(flywheel) and use a coil of wire as the sensor. >>>> >>>> The problem is that I'm getting much lower voltage than I expected. >>>> Faraday's law says the voltage on the coil is the number of turns >>>> times the change in flux. The change in flux depends on the rpm's but >>>> I'm simply using my hand to move the magnet across the coil. I get >>>> something like a sinusoid damped(or alternatively the derivative of >>>> the erf function). I have about 200-300 turns and the coil is getting >>>> unwieldy. >> >>Aircore, or a coil on an E or I section ferrite, bunch of nails? >>Or a magnet, that's how variable reluctance (also guitar) pickups work. >>>> >>>> This is fine but it most I get about 30mV(surely to be much larger >>>> with the flywheel at full speed). What I'm thinking of doing is simply >>>> using an opamp or bjt to act as a switch/comparator but the only >>>> problem I see is that the noise may add extra pulses. >> >>I think opamps are easy, dual 8 pin, there's an 8pin amp + comp? >>>> >>>> Is there a simple way I can increase the noise floor, say, by >>>> offseting the ground of the op amp and effectively setting making dc >>>> negative relative to the opamp. I'm thinking that I could add a >>>> resistor to the -V of the op amp. I only have a + supply. >> >>John L's circuit looks okay for single supply, ac amp -> comparator, >>dual opamp, maybe CMOS, for 5V single supply to match PIC? > > >My circuit is used mostly with variable-reluctance pickups, basically >a rotating ferrous gear which passes near a spark-plug looking pickup, >which is a small rod magnet with a coil around it. > >http://prototype.infolytica.com/en/coolstuff/ex0128/VR_Sensor_380.png > >http://www.phoenixamerica.com/Images/VR%20Grouping%281z3o73%29.jpg > >These give modestly distorted sine wave outputs whose amplitude and >frequency are both roughly proportional to speed, so benefit from an >integrator if used over a wide speed range. A real-world VR pickup >might have output from a few millivolts to 100 volts p-p over a real >speed range. > >I use a similar circuit in my 8-channel VME tach and tach-overspeed >modules. I've sold maybe 400 of them so far, over 3200 channels, and >I've has surprisingly few calls from users having setup difficulties. >The integrator+comparator thing is very forgiving. Yes, you're only after the zero crossings, like FM radio, amplitude doesn't matter much. > >If the OP's pickup makes, say, one short pulse per revolution, the >comparator threshold might be offset to accomodate the more pulse-like >duty cycle. If his speed range is limited, just an amp and a >comparator may be all he needs. Or an opto-chopper, hall effect, reed >relay, or some other switch-type gadget. Or use a self biasing comparator, RC on signal to get chop point reference, it's a common circuit. > >A stepper motor makes a neat speed sensor, behaving just like a VR >pickup. Tons of signal. Rip one out of an old floppy drive or some >such. The signal conditioner might be just an R-C lowpass, diode >clamps maybe, and a comparator, the poor man's integrator. But some paint + optical, or VR on existing gear teeth is much easier ;) A stepper might power LCD tacho display too? Grant. > >John >
From: Grant on 28 Jul 2010 20:48 On Wed, 28 Jul 2010 09:27:08 -0700 (PDT), George Herold <gherold(a)teachspin.com> wrote: >On Jul 27, 9:30 pm, Dookie <abstract.dissona...(a)gmail.com> wrote: >> I have a contact/photo rpm meter but it is acting funky and would like >> to create a simple meter for some testing. >> >> I've created the pic code and seem to have gotten it to work but need >> some sensor to debug it. The pic code basically counts the time >> between pulses. I do not use the ADC but rather the digital inputs and >> monitor when the pin goes high. The code does have built in dead time >> to prevent multiple countings. >> >> My idea was to stick a magnet on the device I want to measure the >> rpms(flywheel) and use a coil of wire as the sensor. >> >> The problem is that I'm getting much lower voltage than I expected. >> Faraday's law says the voltage on the coil is the number of turns >> times the change in flux. The change in flux depends on the rpm's but >> I'm simply using my hand to move the magnet across the coil. I get >> something like a sinusoid damped(or alternatively the derivative of >> the erf function). I have about 200-300 turns and the coil is getting >> unwieldy. >> >> This is fine but it most I get about 30mV(surely to be much larger >> with the flywheel at full speed). What I'm thinking of doing is simply >> using an opamp or bjt to act as a switch/comparator but the only >> problem I see is that the noise may add extra pulses. >> >> Is there a simple way I can increase the noise floor, say, by >> offseting the ground of the op amp and effectively setting making dc >> negative relative to the opamp. I'm thinking that I could add a >> resistor to the -V of the op amp. I only have a + supply. >> >> Or is there any better way that doesn't involve to much work? It >> doesn't have to be completely perfect as I am taking an average for >> the rpm's and can through out outliers. The main thing is to get the >> input to the pic to act digitally. >> >> I know there are a god awefull number of ways to do this but something >> simple with minimum and common parts is what I'm looking for. > >I made a bicycle speedometer for myself many years ago. I used a >magnetic reed relay.. But I couldn't find it listed at digikey and I >suspect I have the wrong name. The relay closed when a magnet was >near. Very simple if you just want a digital pulse... Perhaps someone >will know the correct name of this sensor. Reed switch, couple bike 'computers' I've had use the same concept. Grant. > >George H.
From: markp on 28 Jul 2010 21:05
"Grant" <omg(a)grrr.id.au> wrote in message news:rsj156hcg8q6banbsmtn29q1q6c928g09r(a)4ax.com... > On Wed, 28 Jul 2010 09:27:08 -0700 (PDT), George Herold > <gherold(a)teachspin.com> wrote: > >>On Jul 27, 9:30 pm, Dookie <abstract.dissona...(a)gmail.com> wrote: >>> I have a contact/photo rpm meter but it is acting funky and would like >>> to create a simple meter for some testing. >>> >>> I've created the pic code and seem to have gotten it to work but need >>> some sensor to debug it. The pic code basically counts the time >>> between pulses. I do not use the ADC but rather the digital inputs and >>> monitor when the pin goes high. The code does have built in dead time >>> to prevent multiple countings. >>> >>> My idea was to stick a magnet on the device I want to measure the >>> rpms(flywheel) and use a coil of wire as the sensor. >>> >>> The problem is that I'm getting much lower voltage than I expected. >>> Faraday's law says the voltage on the coil is the number of turns >>> times the change in flux. The change in flux depends on the rpm's but >>> I'm simply using my hand to move the magnet across the coil. I get >>> something like a sinusoid damped(or alternatively the derivative of >>> the erf function). I have about 200-300 turns and the coil is getting >>> unwieldy. >>> >>> This is fine but it most I get about 30mV(surely to be much larger >>> with the flywheel at full speed). What I'm thinking of doing is simply >>> using an opamp or bjt to act as a switch/comparator but the only >>> problem I see is that the noise may add extra pulses. >>> >>> Is there a simple way I can increase the noise floor, say, by >>> offseting the ground of the op amp and effectively setting making dc >>> negative relative to the opamp. I'm thinking that I could add a >>> resistor to the -V of the op amp. I only have a + supply. >>> >>> Or is there any better way that doesn't involve to much work? It >>> doesn't have to be completely perfect as I am taking an average for >>> the rpm's and can through out outliers. The main thing is to get the >>> input to the pic to act digitally. >>> >>> I know there are a god awefull number of ways to do this but something >>> simple with minimum and common parts is what I'm looking for. >> >>I made a bicycle speedometer for myself many years ago. I used a >>magnetic reed relay.. But I couldn't find it listed at digikey and I >>suspect I have the wrong name. The relay closed when a magnet was >>near. Very simple if you just want a digital pulse... Perhaps someone >>will know the correct name of this sensor. > > Reed switch, couple bike 'computers' I've had use the same concept. > > Grant. That would work for low revs, but may have difficulty at high revs due to the mechanical nature of the contacts (they would have inertia, and would probably get mechanically stressed after a while). I'm unsure of the OPs max rpm requirements. Mark. |