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[DPRG]Wall-E -> 1GHZ computers laser rangefinding

Subject: [DPRG]Wall-E -> 1GHZ computers laser rangefinding
From: Kenneth Maxon kmaxon at qwest.net
Date: Thu Jul 24 20:18:52 CDT 2008


Hi Ray,

The frequency I was referring to in the post below, was not the frequency of
the modulation, but rather the fundamental frequency or wavelength of the
light itself?  Is your laser in the visible spectrum?  What is the
wavelength in Nm?  Optical filters are not going to interact with the
extremely low modulation frequencies.

-Kenneth


-----Original Message-----
From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org]On
Behalf Of ray xu
Sent: Thursday, July 24, 2008 3:17 PM
To: dprglist at dprg.org
Subject: RE: [DPRG]Wall-E -> 1GHZ computers laser rangefinding



I will be modulating it at low frequency; like 1 or 2 kHz, but not below
70Hz.  I am also not sure that if the unwanted light is in the same
wavelength (I don't have a light meter); but I'm assuming there is because
the sun light is triggering my sensor.

The sensor I'm using is a PNZ334; I noticed on my scope that it is a hybrid
of digital and analog.  Most of the time its either 5 volts or none; but if
a VERY tiny laser beam is detected, its somewhere in between.

And yes, the difference between the sun's (or even my bedroom lamp) energy
vs. my laser's energy is very big.

I am also not familiar about electronics filters, but I barely know them.

___________________
Ray Xu
rayxu at tx.rr.com
DPRG member
OOPic group member
Seattle Robotics group member
My Blog


-----Original Message-----
From: Kenneth Maxon [mailto:kmaxon at qwest.net]
Sent: Wednesday, July 23, 2008 7:19 PM
To: ray xu; dprglist at dprg.org
Subject: RE: [DPRG]Wall-E -> 1GHZ computers laser rangefinding



Ray,

What frequency range are the laser and receiver pair.  In general this will
be a problem with most visible light laser systems as the sun (and many
other sources) put out energy across a large portion of the spectrum.   So
adding high-Q notch filter can help if the sensitivity of the receiver
extends beyond the frequency range of the signal to be sampled, however if
the interference is on the same frequency range as the signal to be
detected, then the problem is more complex and a simple optical filter *may*
not help.

In the paragraph above I use the word *may* not help as there are cases
where it can.   If the broad spectrum that is bleeding across the frequency
of interest is of a much lower amplitude than the signal returned to the
senor, then an optical filter can indeed help.   In this case an appropriate
optical filter can be used to drop the transmission of ALL frequencies
reaching the sensor.  This helps because all frequencies can be lowered to
the point where the undesired broad band noise no longer triggers or is
measurable by the sensor.

If the sensor has an analog output and modulation is the method of choice,
then an electronic filter *May* be of use.  The limiting issue here again
will be how much the returned signal stimulates the sensor vs how much the
background noise stimulates the sensor.  (SNR = Signal to Noise Ratio)  If
there is significant difference between the two, then an electronic band
pass filter and a modulated source will be able to detect the signal.  (This
of course assumes the sensor is not being used near saturation point,
otherwise both methods will be necessary (optical and electronic))...

-Kenneth

-----Original Message-----
From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org]On
Behalf Of ray xu
Sent: Wednesday, July 23, 2008 3:48 PM
To: dprglist at dprg.org
Subject: RE: [DPRG]Wall-E -> 1GHZ computers laser rangefinding


My receiver is picking up ambient light.  Are there any ways to filter that
out?  Should I modulate my laser and put a bandpass filter on the receiver
end?

___________________
Ray Xu
rayxu at tx.rr.com
DPRG member
OOPic group member
Seattle Robotics group member
My Blog





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