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

Subject: [DPRG]Wall-E -> 1GHZ computers laser rangefinding
From: Ed Paradis legomaniac at gmail.com
Date: Fri Jul 25 10:36:00 CDT 2008

Just a side note,

If anyone wants any exposed/unexposed/developed/undeveloped black and
white film, I have tons for free.

For reference, a roll of black and white film costs about $5-$10.  I
don't know if it makes a difference, but there are two types of black
and white film out there:  one is 'real' black and white and the other
is color film made to be black and white.  You want the former.  The
latter is processed using the "C-41 process".

Ed

On Fri, Jul 25, 2008 at 12:43 AM, Ted Larson <ted at larsonland.com> wrote:
> Ray,
>
> The way you deal with background noise....i.e. sunlight....is to modulate
> the signal at a known carrier frequency, and send pulses of the modulated
> carrier.  So, run it at like 56khz, and then 1 to 2ms pulses of it.  Most
> people use an op-amp setup sensitive to the carrier frequency, and then look
> for the edges of your 1 to 2ms pulses.  This is how IR remote controls work,
> and sonar systems work, and most optoelectronic systems work.  This is what
> Ken is referring to when he talks about the frequency you are going to
> modulate the signal at;  The carrier frequency you are modulating the light
> at.
>
> There is a reason most laser ranging systems don't use visible light, and
> are infrared.  It is too hard to separate a bounced signal from background
> noise.  Again, typically IR systems use optical filters for IR only, and
> then analog filters on the output of the photodiode matched to the modulated
> carrier frequency, to eliminate the background.  Even with all this, it is
> still difficult to get good reflections, from various substances the
> transmitter might encounter.  The worlds cheapest optical IR filter, is a
> piece of exposed photographic film.  Go buy a cheap roll of BW 35mm film,
> pull it out of the can outside, cut off a piece...bingo...IR filter.
>
> So...the first thing you are going to need to do is figure out how to
> modulate your laser at a carrier frequency.  When you hook your photodiode
> up the way you are describing, you should see your nice modulated carrier
> coming out the other side when you turn it on continuously.  Then, you will
> need to build an amplifier/filter circuit for the photodiode that is
> sensitive to that carrier frequency only, and you will be ready to see it
> work when you pulse the laser.
>
> Just my 2 cents...
>
> -Ted
>
>
>
>
>
> -----Original Message-----
> From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org] On Behalf
> Of ray xu
> Sent: Thursday, July 24, 2008 1:17 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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