| Author |
Message |
Guest
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 Posted:
Wed May 04, 2005 12:35 am Post subject:
voltage pulse sensor |
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Could someone please help me locate a voltmeter, low cost, that will
detect a voltage pulse less than 120ms in length and about 120mV (give
or take 30mV) amplitude? All I really need it to do is flash an LED
when a pulse is detected. I do not need to know the voltage, period,
etc.. I only need to know that a pulse was detected. I am having
trouble finding the equipment through digikey, etc..
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Robert Baer
Guest
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| Posted:
Wed May 04, 2005 8:35 am Post subject:
Re: voltage pulse sensor |
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dwfox1977@gmail.com wrote:
| Quote: | Could someone please help me locate a voltmeter, low cost, that will
detect a voltage pulse less than 120ms in length and about 120mV (give
or take 30mV) amplitude? All I really need it to do is flash an LED
when a pulse is detected. I do not need to know the voltage, period,
etc.. I only need to know that a pulse was detected. I am having
trouble finding the equipment through digikey, etc..
Errr..... |
Say you bought a *meter* that could detect pulses like that, and say
it gave readings of pulse width and amplitude.
Then what?
The meter would be useless for doing something else, specifically
flashing an LED.
You do not want or need a meter.
Some simple logic and timers will do the job.
The input pulse could drive a comparitor (or two) to determine
amplitude (or amplitude range); the output feeds a one-shot and logic to
determine pulse width, and the output then drives an LED flasher (a
timer and driver). |
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DaveM
Guest
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| Posted:
Wed May 04, 2005 4:35 pm Post subject:
Re: voltage pulse sensor |
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"Robert Baer" <robertbaer@earthlink.net> wrote in message
news:xAYde.6514$BE3.1848@newsread2.news.pas.earthlink.net...
| Quote: | dwfox1977@gmail.com wrote:
Could someone please help me locate a voltmeter, low cost, that will
detect a voltage pulse less than 120ms in length and about 120mV (give
or take 30mV) amplitude? All I really need it to do is flash an LED
when a pulse is detected. I do not need to know the voltage, period,
etc.. I only need to know that a pulse was detected. I am having
trouble finding the equipment through digikey, etc..
Errr.....
Say you bought a *meter* that could detect pulses like that, and say it
gave readings of pulse width and amplitude.
Then what?
The meter would be useless for doing something else, specifically
flashing an LED.
You do not want or need a meter.
Some simple logic and timers will do the job.
The input pulse could drive a comparitor (or two) to determine amplitude
(or amplitude range); the output feeds a one-shot and logic to determine
pulse width, and the output then drives an LED flasher (a timer and
driver).
|
The operative term for what you need is a Pulse Stretcher.
Take a look at the datasheet for the LM555 timer.
http://www.national.com/ds/LM/LM555.pdf
The LM555 will do what you want in monostable mode. The datasheet describes
the circuit and equations to design it.
If you don't feel that you can handle the details of designing the circuit,
you might download freebie designer software at
http://www.schematica.com/555_Timer_design/555.htm and let your computer do
the work for you. For the output pulse width, you would probably have to
use something in the neighborhood of 250 ms in order to make the flash of
the LED visible.
Amplitude is a minor problem here, since your pulse is too low to trigger
the 555 timer. A simple opamp or comparator circuit will do the job nicely.
If you try this approach, first select the 555 Monostable button, then
select either the Positive Edge Triggered Monostable or the Negative Edge
Triggered Monostable, depending on the polarity of the pulse coming from the
opamp/comparator.
If you're only driving a single LED, the 555 output can drive it directly.
Be sure to put a limiting resistor in series with the LED.
--
Dave M
MasonDG44 at comcast dot net (Just subsitute the appropriate characters in
the address)
Never take a laxative and a sleeping pill at the same time!!
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John - KD5YI
Guest
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| Posted:
Fri May 06, 2005 7:35 am Post subject:
Re: voltage pulse sensor |
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dwfox1977@gmail.com wrote:
| Quote: | Could someone please help me locate a voltmeter, low cost, that will
detect a voltage pulse less than 120ms in length and about 120mV (give
or take 30mV) amplitude? All I really need it to do is flash an LED
when a pulse is detected. I do not need to know the voltage, period,
etc.. I only need to know that a pulse was detected. I am having
trouble finding the equipment through digikey, etc..
|
Have you tried looking for a Logic Probe?
Good luck.
John |
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