Counting Pulses (ratemeter) or sensing a weak signal

Discussion in 'General Electronics Chat' started by -Ryder-, Jun 14, 2018.

  1. -Ryder-

    Thread Starter New Member

    Jun 14, 2018
    10
    1
    Hi all,

    I'm not looking to design a circuit so much as find a device to discover a signal.

    The application is a laser looking at a rapidly spinning object (about 60,000 rpm), and detecting that it is in fact spinning. Measuring the rate is NOT important to me... however I am getting about a 1kHz signal from the sensor so that's all fine and dandy.

    I need to detect simply this: am I getting a signal or not? (is it spinning or not)

    I would use a simple ratemeter, but they require signal levels the laser sensor does not achieve.

    The signal is about 0.3v, 1kHz, offset by +1 volts (so it's swinging between 1.0 v and 1.3v).

    The only options I can think of is to process this signal so that it is amplified to about a 5v signal, having shifted the offset down so that it more resembles a logic signal (0 to 5v swing)... then feed it into a common ratemeter, OR find a device that can detect the 0.3v signal and illuminate an LED or something to say that the signal is detected.

    Again, not looking to make a circuit... but looking for a device that can do either of these jobs.

    Sorry for the weak electronics... it's not my field, trying my best.

    Thanks!

    R
     
  2. -Ryder-

    Thread Starter New Member

    Jun 14, 2018
    10
    1
    I can't figure out how to edit my original post... so I'll add this:

    Would a Cymometer likely work?
     
  3. jpanhalt

    Expert

    Jan 18, 2008
    6,038
    1,052
    Hi Ryder,

    Welcome to AAC.

    Why display the signal? You still need to detect it, presumably, digitally. Have you considered a comparator? Many MCU's have a comparator built in.

    Edit: With an MCU it would be very easy to calculate the spin rate too.
     
    Last edited: Jun 14, 2018
  4. wayneh

    Expert

    Sep 9, 2010
    14,518
    5,074
    What sort of sensor is this? I'm trying to understand what it produces when NO rotation is sensed versus spinning. When spinning is detected, it produces a waveform between 1.0 and 1.3V? The frequency is always 1kHz?

    I think a simple comparator circuit may be all you need. You could flash an LED any time the voltage exceeds, say, 1.1 volts. If it flashes at 1 kHz, it'll appear fully on and it won't matter that it's off some of the time.

    Lots of ways to skin this cat.
     
  5. -Ryder-

    Thread Starter New Member

    Jun 14, 2018
    10
    1
    Thank you for the reply.

    The signal will be a more or less steady voltage between 1.0 and 1.3 volts... indeterminate, when there is no rotation.

    When it is detecting rotation I get something approximating a sine wave at ~1kHz going 1.0 to 1.3 volts.
     
  6. -live wire-

    Active Member

    Dec 22, 2017
    501
    40
    You are a traitor to your kind! I would never expect this from you. How could you do that?!?;)

    Maybe add a series capacitor to filter out what is essentially DC and then if a significant amount of current passes through do something with that. That is, if your sensor outputs high/low based on it being blocked. You could make a comparator circuit to do that if that is not the case.
     
  7. -Ryder-

    Thread Starter New Member

    Jun 14, 2018
    10
    1
    Thank you for the reply. I don't strictly need to display a count. I could go with a "go/no-go" detection arrangement.

    Keep in mind, I am trying to avoid creating a circuit... and instead want a device to do this job (produced by a reputable company preferably!)

    Thank you for your kind help!

    R
     
  8. -Ryder-

    Thread Starter New Member

    Jun 14, 2018
    10
    1
    Thank you...

    Don't want to make a circuit. There are some multimeters with frequency setting... I don't know the signal requirements for detection on a DVM, but somehow I don't think 0.3v will cut it!

    Best regards,

    R
     
  9. wayneh

    Expert

    Sep 9, 2010
    14,518
    5,074
    What is different about the sensor output, spinning versus not?
     
  10. danadak

    Active Member

    Mar 10, 2018
    847
    182
    Questions -

    1) Is object return signal/reflectance of object, always consistent ?
    2) What do you want to know -
    a. RPM too high
    b. RPM too low
    c. RPM = 0
    d. Actual RPM, if so accuracy needed
    e. Data available on web or just local
    3) Signal noisy ? Need filtering before processing ?

    Regards, Dana.
     
  11. jpanhalt

    Expert

    Jan 18, 2008
    6,038
    1,052
    This is an electronics forum, not Amazon.;)

    Maybe your voltmeter idea will work. Have you tried it?
     
  12. -Ryder-

    Thread Starter New Member

    Jun 14, 2018
    10
    1
    Hi Dana,

    Great questions.

    1- I can't count on it being very consistant, but only time will tell. My expectation is that it the signal may vary in amplitude and offset up to 50%... so robust detection may be a thing.

    2-
    a - not needed
    b - not not needed
    c - yes... I need to see this (the signal from the sensor is flat, between 1.0 and 1.3v approx)
    d - not needed
    e - local, real-time

    3. The signal is clean.

    Thank you for your kind help,

    R
     
  13. -Ryder-

    Thread Starter New Member

    Jun 14, 2018
    10
    1
    Instrumentation is a part of electronics :)

    One answer to my problem is an o-scope... (which is how I know what the signal looks like) but unfortunately, size/cost/complexity are a factor in final implementation, so an O-scope is out of the question (or is it? Are their companies that make miniature/uber-cheap o-scopes?)
     
  14. danadak

    Active Member

    Mar 10, 2018
    847
    182
    You can start with a PC sound card based scope for free. Will give you basically
    audio range scope, spectrum analyzer, and function generator all using your
    PC sound card.


    https://www.zeitnitz.eu/scope_en


    http://www.zelscope.com/


    http://www.ledametrix.com/oscope/


    http://www.virtins.com/downloads.shtml


    But first build a simple circuit to protect sound card inputs so you do not
    ruin from transients, overvoltage. Google "protect sound card input".


    For example http://makezine.com/projects/sound-card-oscilloscope/


    Sound card impedance bridge -


    http://www.marucchi.it/ZRLC_web/ZRLC/Steber_An_LMS_Impedance_Bridge.pdf


    http://www.sillanumsoft.org/ZRLC.htm


    There is low cost logic analyzer, good to several Mhz, ~ $10

    https://www.ebay.com/itm/USB-Logic-...270582?hash=item25f26191f6:g:Xs4AAOSwQ7haxEa1

    https://www.saleae.com/downloads/


    Search ebay for USB oscilloscope, quite a few offerings that will get you >> 1 Mhz.



    Regards, Dana.
     
    Last edited: Jun 14, 2018
    -Ryder- likes this.
  15. -Ryder-

    Thread Starter New Member

    Jun 14, 2018
    10
    1
    I think we have a winner :)

    Thanks, Dana!

    R
     
  16. danadak

    Active Member

    Mar 10, 2018
    847
    182
    As far as the problem at hand I would approach it using an
    PGA (programmable gain amplifier) followed by a comparator
    to square the signal and then a basic freq cntr.

    Additionally a cal loop using an A/D and a DAC, DAC to modify
    offset, A/D to measure P-P, and create AGC (by changing PGA
    gain) so signal is consistent.

    I would do it with a PSOC as it has all the basic elements to do this
    on one chip. Rough config attached.



    Regards, Dana.
     
  17. Sensacell

    Moderator

    Jun 19, 2012
    1,799
    519
    The only thing that will do this off-the-shelf would be a fancy programmable voltmeter with remote interface capabilities.

    You would basically program it to give you a Go / No Go output, based on the variation in the signal.
    Not a good plan- it's going to be expensive and you need to learn a whole bunch of crap you don't want /need to.

    http://www.ni.com/tutorial/54214/en/

    Wayyyy cheaper - faster - easier to build a circuit.
     
  18. wayneh

    Expert

    Sep 9, 2010
    14,518
    5,074
    I'd just use a capacitor to couple to a small speaker. Audible tone equals spinning. Done.
     
    MrChips likes this.
  19. danadak

    Active Member

    Mar 10, 2018
    847
    182
    Great hearing at 60 Khz.

    Regards, Dana.
     
  20. MrChips

    Moderator

    Oct 2, 2009
    16,143
    4,952
    It is 60,000rpm = 1kHz, not 60kHz.
     
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