Tachometer
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Posts: 46,084
>>>
Date: Fri, 10 Mar 2000 18:10:45 -0800 (PST)
From: Alejandro Vazquez <alexvazquez@y...>
I have to do a tachometer for my school, but I dont
want to use the BS2,, How can I build it......
<<<<
A common way to do this is by discharging a capacitor,
which has been charged to a fixed voltage before
discharge, into a moving coil meter. The number of
discharges per time averages in the meter to
give a reading proportional to number of pulses per
time.
This can be done with a single pole double throw
relay [noparse][[/noparse]or solid state circuitry] so that the
capacitor is first charged to a reference voltage
and then discharged through the meter. [noparse][[/noparse]The capacitor
is put to the relay pole and one throw goes to the
meter, the other to +Vref. other end of the capacitor
goes to Vref- as does the other side of the meter].
The realy coil is actuated off and on at the frequency
to be measured.
There is also a tachometer IC the LM2917 [noparse][[/noparse]LM2907 8pin].
Look up the data sheet at the National Semiconductor
web site. [noparse][[/noparse]Frequency to voltage converter]. good luck.
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Date: Fri, 10 Mar 2000 18:10:45 -0800 (PST)
From: Alejandro Vazquez <alexvazquez@y...>
I have to do a tachometer for my school, but I dont
want to use the BS2,, How can I build it......
<<<<
A common way to do this is by discharging a capacitor,
which has been charged to a fixed voltage before
discharge, into a moving coil meter. The number of
discharges per time averages in the meter to
give a reading proportional to number of pulses per
time.
This can be done with a single pole double throw
relay [noparse][[/noparse]or solid state circuitry] so that the
capacitor is first charged to a reference voltage
and then discharged through the meter. [noparse][[/noparse]The capacitor
is put to the relay pole and one throw goes to the
meter, the other to +Vref. other end of the capacitor
goes to Vref- as does the other side of the meter].
The realy coil is actuated off and on at the frequency
to be measured.
There is also a tachometer IC the LM2917 [noparse][[/noparse]LM2907 8pin].
Look up the data sheet at the National Semiconductor
web site. [noparse][[/noparse]Frequency to voltage converter]. good luck.
________________________________________________________________
YOU'RE PAYING TOO MUCH FOR THE INTERNET!
Juno now offers FREE Internet Access!
Try it today - there's no risk! For your FREE software, visit:
http://dl.www.juno.com/get/tagj.
Comments
tachometer.
I already have the input pulses,,, I get the pulses
from a opto sensor and then a 555 timer to convert the
signal from the opto sensor to a square signal.
I tried to connect the BS2 to the input pulses using
pulsin but I dont know how to get it in RPM.
The other problem I saw is that I put a disk on the
opto sensor and I spin it about 1 revolution per
second and in the BS2 I cant get any response,,,, only
when the disk is going faster.....
Please Need Help
Thanks
Alex
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readout. I am using a disk that is 1/2 reflective and 1/2 non-reflective so
the pulse I am measuring is the period of 1 rotation. Also, due to the way I
am handling the math I only get a sensitivity of 10 rpm increments.
i is a word variable and markings is the number of divisions on the wheel (2
in this case). The reason I check for a value over 10000 is that I was
getting some erroneous readings and it was always a ridiculously high number
(Think it has to do with my poor opto sensor mounting, I keep wiggling as I
hold it). So I decided that the max RPM I would ever use this on is 10K and
this code makes it keep reading and calculating until I get a value that is
in my range of plausibility.
Tach:
PulsIn PORTB.0,0,pulse
i = (6000/((pulse/100)*markings))*10
IF i > 10000 Then
GoTo Tach
EndIF
That should get you a tach readout.
Tim
[noparse][[/noparse]Denver, CO]
>
Original Message
> From: Alejandro Vazquez [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=JyjMjlGc6IBvZgMYHfB7jdM2QTnho5TznxEg8-olpAdahhSMyXx6xUhzi-12TOKbCmTlGqSeQgaXB3Y]alexvazquez@y...[/url
> Sent: Friday, May 12, 2000 9:18 PM
> To: basicstamps@egroups.com
> Subject: [noparse][[/noparse]basicstamps] Tachometer
>
>
> I need urgent help for a school project of a
> tachometer.
>
> I already have the input pulses,,, I get the pulses
> from a opto sensor and then a 555 timer to convert the
> signal from the opto sensor to a square signal.
>
> I tried to connect the BS2 to the input pulses using
> pulsin but I dont know how to get it in RPM.
>
> The other problem I saw is that I put a disk on the
> opto sensor and I spin it about 1 revolution per
> second and in the BS2 I cant get any response,,,, only
> when the disk is going faster.....
>
>
> Please Need Help
>
>
> Thanks
> Alex
>
> __________________________________________________
> Do You Yahoo!?
> Send instant messages & get email alerts with Yahoo! Messenger.
> http://im.yahoo.com/
>
>
>
>
>I tried to connect the BS2 to the input pulses using
>pulsin but I dont know how to get it in RPM.
>The other problem I saw is that I put a disk on the
>opto sensor and I spin it about 1 revolution per
>second and in the BS2 I cant get any response,,,, only
>when the disk is going faster.....
The maximum allowable value of PULSIN is 65535+2=0.13107 second. So your
pulses have to arrive at about ten per second, or else the Stamp won't
catch them right.
Tim suggested:
>Here is some code I am using on a PICBasic Pro program to give me a tach
>readout. I am using a disk that is 1/2 reflective and 1/2 non-reflective
so
>the pulse I am measuring is the period of 1 rotation. Also, due to the way
I
>am handling the math I only get a sensitivity of 10 rpm increments.> Tach:
> PulsIn PORTB.0,0,pulse
> i = (6000/((pulse/100)*markings))*10
> IF i > 10000 Then
> GoTo Tach
> EndIF
The resolution can be improved by making the numerator as large as
possible, in this case 60000 instead of 6000:
i = (60000/((pulse/100)*markings)) ' markings=2
That gives 45 RPM to 10000 RPM, when the "pulse" value ranges from 300 up
to 65535. The best resolution for PBASIC in solving Y=C/X comes when the
value of X is near the square root of C. The resolution can be improved
both mechanically and mathemtically by using more markings. There are ways
to improve the math by "faking" a larger numerator or by using long
division.
-- Tracy Allen
Electronically Monitored Ecosystems
http://www.emesystems.com
Thanks for the tweak on the formula. I just updated my program with it and
added a loop to average 6 reading and it is now giving a nice stable readout
that looks much better than just seeing everything as a multiple of 10 RPM.
I am driving a MAX7219 with it and plan on using it for a readout of my RPM
on the mill head of my Shoptask 3 in 1 machine. I put on a variable speed
motor in place of the stock fixed speed and stepped pulleys. My maximum
spindle speed is about 5000 RPM and my minimum is about 100 RPM so the range
will work perfectly.
Tim
[noparse][[/noparse]Denver, CO]
>
Original Message
> From: Tracy Allen [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=DZLTh2v317CCyDM2Y1I-IZqeIg_R-dKdCgfdLyzUNsMOicXnsxfLx9oQX0qZsZL1x7aj0nrQfqqsRKM]emesys@c...[/url
> Sent: Saturday, May 13, 2000 11:45 AM
> To: INTERNET:basicstamps@egroups.com
> Subject: RE: [noparse][[/noparse]basicstamps] Tachometer
>
>
>
> Alex asked:
> >I tried to connect the BS2 to the input pulses using
> >pulsin but I dont know how to get it in RPM.
> >The other problem I saw is that I put a disk on the
> >opto sensor and I spin it about 1 revolution per
> >second and in the BS2 I cant get any response,,,, only
> >when the disk is going faster.....
>
> The maximum allowable value of PULSIN is 65535+2=0.13107 second. So your
> pulses have to arrive at about ten per second, or else the Stamp won't
> catch them right.
>
>
> Tim suggested:
> >Here is some code I am using on a PICBasic Pro program to give me a tach
> >readout. I am using a disk that is 1/2 reflective and 1/2 non-reflective
> so
> >the pulse I am measuring is the period of 1 rotation. Also, due
> to the way
> I
> >am handling the math I only get a sensitivity of 10 rpm
> increments.> Tach:
> > PulsIn PORTB.0,0,pulse
> > i = (6000/((pulse/100)*markings))*10
> > IF i > 10000 Then
> > GoTo Tach
> > EndIF
>
> The resolution can be improved by making the numerator as large as
> possible, in this case 60000 instead of 6000:
>
> i = (60000/((pulse/100)*markings)) ' markings=2
>
> That gives 45 RPM to 10000 RPM, when the "pulse" value ranges from 300 up
> to 65535. The best resolution for PBASIC in solving Y=C/X comes when the
> value of X is near the square root of C. The resolution can be improved
> both mechanically and mathemtically by using more markings.
> There are ways
> to improve the math by "faking" a larger numerator or by using long
> division.
>
> -- Tracy Allen
> Electronically Monitored Ecosystems
> http://www.emesystems.com
>
>
>
>
>
the a/d will probably be 0-5 volt or 0-10 volt
a simple divider resistor network will allow you to cut down the tach output
to max level for the a/d. You will need to decide how much resolution you
require (either 8 or 10 or 12 bit)
Richard
Original Message
From: "Production Technology, L.L.C." <fixemerd@a...>
To: <basicstamps@yahoogroups.com>
Cc: <fixemerd@a...>
Sent: Monday, August 20, 2001 11:37 AM
Subject: [noparse][[/noparse]basicstamps] TACHOMETER
> Fellow Stampers,
>
> Does anyone have a good idea how to read a tachometer. This
particular
> tachometer outputs a voltage ±14.00 volts proportional to speed and
> direction. I assume I need a ADC, however, am not sure if that is
correct,
> and if it is, what ADC will let you compare two inputs?
>
> David Fixemer
> fixemerd@a...
> 402-472-8239
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
you will only need one channel a/d
I believe that you need to offset the output by 14 volts so that it swings
from 0 to 28 volts.
Now use the advice that I gave about the voltage divider, resolution, etc.
your code will know that now 14 volts is stationary and that 0 volts is full
speed cw and that 28 volts is full speed ccw
Richard
Original Message
From: "Production Technology, L.L.C." <fixemerd@a...>
To: <basicstamps@yahoogroups.com>
Cc: <fixemerd@a...>
Sent: Monday, August 20, 2001 11:37 AM
Subject: [noparse][[/noparse]basicstamps] TACHOMETER
> Fellow Stampers,
>
> Does anyone have a good idea how to read a tachometer. This
particular
> tachometer outputs a voltage ±14.00 volts proportional to speed and
> direction. I assume I need a ADC, however, am not sure if that is
correct,
> and if it is, what ADC will let you compare two inputs?
>
> David Fixemer
> fixemerd@a...
> 402-472-8239
>
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and
Body of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
Does anyone have a good idea how to read a tachometer. This particular
tachometer outputs a voltage ±14.00 volts proportional to speed and
direction. I assume I need a ADC, however, am not sure if that is correct,
and if it is, what ADC will let you compare two inputs?
David Fixemer
fixemerd@a...
402-472-8239
scale the output of the tach to use a -2.5/+2.5 input range. Sample a
part in from Maxim or Analog Devices. Cheaper that way when you find
out that a $40 A/D isn't going to work. Also you probably want to use
a serial A/D so that you only have to use 3 I/O pins on the BS.
Jason
--- In basicstamps@y..., "Richard Friedrich" <rfriedrich@a...> wrote:
> whoops, Now I realize what you are asking
>
> you will only need one channel a/d
>
> I believe that you need to offset the output by 14 volts so that
it swings
> from 0 to 28 volts.
>
> Now use the advice that I gave about the voltage divider,
resolution, etc.
>
> your code will know that now 14 volts is stationary and that 0
volts is full
> speed cw and that 28 volts is full speed ccw
>
>
> Richard
>
>
>
>
Original Message
> From: "Production Technology, L.L.C." <fixemerd@a...>
> To: <basicstamps@y...>
> Cc: <fixemerd@a...>
> Sent: Monday, August 20, 2001 11:37 AM
> Subject: [noparse][[/noparse]basicstamps] TACHOMETER
>
>
> > Fellow Stampers,
> >
> > Does anyone have a good idea how to read a tachometer. This
> particular
> > tachometer outputs a voltage ±14.00 volts proportional to speed
and
> > direction. I assume I need a ADC, however, am not sure if that is
> correct,
> > and if it is, what ADC will let you compare two inputs?
> >
> > David Fixemer
> > fixemerd@a...
> > 402-472-8239
> >
> >
> >
> > To UNSUBSCRIBE, just send mail to:
> > basicstamps-unsubscribe@y...
> > from the same email address that you subscribed. Text in the
Subject and
> Body of the message will be ignored.
> >
> >
> > Your use of Yahoo! Groups is subject to
http://docs.yahoo.com/info/terms/
> >
> >
multi-tasking so you will loose RPM data while the BS is running the
serial in/out command. There are micro controllers that are
multitasking, which are more suitable to use for RPM data acquisition.
multi-tasking so you will loose RPM data while the BS is running the
serial in/out command. There are micro controllers that are
multitasking, which are more suitable to use for RPM data acquisition.
>Correct me if I'm wrong here, The BS is a great device but isn't
>multi-tasking so you will loose RPM data while the BS is running the
>serial in/out command. There are micro controllers that are
>multitasking, which are more suitable to use for RPM data acquisition.
But... it would be a bit unusual for the RPM to change so drastically
during serin/serout time that this short interruption matters
significantly. I'd be inclined to average several determinations, then
display that average, average several more, display that average, or maybe
keep a running 3 or 5 sample average that is displayed after each internal
update, whatever. Otherwise you are likely to get a jittery readout that
is very annoying in a digital display device. Jittery not because the RPM
is really changing, but because the conversion process isn't precisely
repetitive. A bit of the BS's time spent resolving this issue will be a
good thing, not a bad thing.
73 de Jim, KB3PU
I've seen a few postings for petrol engine tachometer projects, and wondered
if anyone has had sucess with tachometer design using a Stamps.
It occurred to me that one fairly simple method would be to connect a 10K
resister at the point where the contact breaker meets the coil. I would
then diode clamp the output to make a 5v. squarewave. I might need to
debounce the contacts using a 555 monostable and would probably need to slow
the pulses down to Stamp speed with a divide by 100 prescaler before the
pulses hit the Stamp.
Any thoughts?
Tony