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Small pulsed voltage

ArchiverArchiver Posts: 46,084
edited 2003-10-29 23:21 in General Discussion
Hey guys,

I've got to resolve a wind speed from some equipment.

I get 3 pulses per revolution from a 'tristate' magnet....(not sure about
this..but it's what the guy said! [noparse]:p[/noparse] )
As it speeds up, the pulses increase in frequency (uh..duh!)...but the
voltage level goes up slightly.
I DON'T believe the voltage gets to any great level....SO....
If stuck with a signal level around 200mV-500mV....I don't want to use too
many components or lose any pulses/resolution....

OpAmp the easiest way?
I thought of a Freq-to-Voltage converter chip that I got...but STILL...low
levels eh!
Uh....I'm thinking and typing here....3906npn....

Pulsed goes through the base with the collector to Vdd and emitter to Vss
(Vdd=+5; Vss=Gnd).
Toss a couple resistors and maybe a cap...:S
Have to keep the component count down....

Ah Well

sb

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2003-10-29 16:06
    Sorry if this is a double post...I didn't see in come out in the group so
    I'm sending it again!


    Hey guys,

    I've got to resolve a wind speed from some equipment.

    I get 3 pulses per revolution from a 'tristate' magnet....(not sure about
    this..but it's what the guy said! [noparse]:p[/noparse] ) As it speeds up, the pulses increase
    in frequency (uh..duh!)...but the voltage level goes up slightly. I DON'T
    believe the voltage gets to any great level....SO.... If stuck with a signal
    level around 200mV-500mV....I don't want to use too many components or lose
    any pulses/resolution....

    OpAmp the easiest way?
    I thought of a Freq-to-Voltage converter chip that I got...but STILL...low
    levels eh! Uh....I'm thinking and typing here....3906npn....

    Pulsed goes through the base with the collector to Vdd and emitter to Vss
    (Vdd=+5; Vss=Gnd). Toss a couple resistors and maybe a cap...:S Have to keep
    the component count down....

    Ah Well

    sb
  • ArchiverArchiver Posts: 46,084
    edited 2003-10-29 20:03
    Steven,

    I don't think the 3904 will work. You will need about 0.6 volts minimum to
    overcome the Base Emitter Junction.

    I think an op-amp comparitor (LM311) will work well. Set up a simple voltage
    divider so the minus lead is at 0.3 volts.

    The only problem I see with this solution is "part/pin" count. Of course the
    3904 is 3 leads and a few resistors.
    The LM311 is an 8p pin dip, and a few resistors.

    Ken
    Hey guys,

    I've got to resolve a wind speed from some equipment.

    I get 3 pulses per revolution from a 'tristate' magnet....(not sure about
    this..but it's what the guy said! [noparse]:p[/noparse] )
    As it speeds up, the pulses increase in frequency (uh..duh!)...but the
    voltage level goes up slightly.
    I DON'T believe the voltage gets to any great level....SO....
    If stuck with a signal level around 200mV-500mV....I don't want to use too
    many components or lose any pulses/resolution....

    OpAmp the easiest way?
    I thought of a Freq-to-Voltage converter chip that I got...but STILL...low
    levels eh!
    Uh....I'm thinking and typing here....3906npn....

    Pulsed goes through the base with the collector to Vdd and emitter to Vss
    (Vdd=+5; Vss=Gnd).
    Toss a couple resistors and maybe a cap...:S
    Have to keep the component count down....

    Ah Well


    [noparse][[/noparse]Non-text portions of this message have been removed]
  • ArchiverArchiver Posts: 46,084
    edited 2003-10-29 23:21
    Which wind gage is it? Some have magnet on the moving shaft, which
    as it turns induces a voltage in a coil on the stator. (Classic
    tachometer). Both the frequency and the voltage increase as the cups
    go around faster, as you noted. The voltage is AC, from 10
    millivolts up to several hundred millivolts.

    The LM2917 is a tachometer interface circuit. It can be configured
    as a frequency to voltage converter, or, for COUNTing, it can put out
    conditioned 5 volt pulses (8-pin dip + a couple of Rs).

    -- Tracy


    >Sorry if this is a double post...I didn't see in come out in the group so
    >I'm sending it again!
    >
    >
    >Hey guys,
    >
    >I've got to resolve a wind speed from some equipment.
    >
    >I get 3 pulses per revolution from a 'tristate' magnet....(not sure about
    >this..but it's what the guy said! [noparse]:p[/noparse] ) As it speeds up, the pulses increase
    >in frequency (uh..duh!)...but the voltage level goes up slightly. I DON'T
    >believe the voltage gets to any great level....SO.... If stuck with a signal
    >level around 200mV-500mV....I don't want to use too many components or lose
    >any pulses/resolution....
    >
    >OpAmp the easiest way?
    >I thought of a Freq-to-Voltage converter chip that I got...but STILL...low
    >levels eh! Uh....I'm thinking and typing here....3906npn....
    >
    >Pulsed goes through the base with the collector to Vdd and emitter to Vss
    >(Vdd=+5; Vss=Gnd). Toss a couple resistors and maybe a cap...:S Have to keep
    >the component count down....
    >
    >Ah Well
    >
    >sb
    >
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