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From: krw on 21 Mar 2010 20:09
On Sun, 21 Mar 2010 16:48:02 -0700, Joerg <invalid(a)invalid.invalid> wrote:

>Grant wrote:
>> On Sun, 21 Mar 2010 14:06:38 -0700, Joerg <invalid(a)invalid.invalid> wrote:
>>
>>> Phil Hobbs wrote:
>>>> On 3/19/2010 11:50 AM, Joerg wrote:
>>>>> markp wrote:
>>>>>> "markp" <map.nospam(a)f2s.com> wrote in message
>>>>>> news:80h62eF4g7U1(a)mid.individual.net...
>>>>>>> "Grant" <omg(a)grrr.id.au> wrote in message
>>>>>>> news:2an6q5le2ev2v7o81mqanp9ua14jqu7s5h(a)4ax.com...
>>>>>>>> On Fri, 19 Mar 2010 03:14:04 -0700,
>>>>>>>> "JosephKK"<quiettechblue(a)yahoo.com> wrote:
>>>>>>>>
>>>>>>>>> On Thu, 18 Mar 2010 18:17:19 -0000, "markp" <map.nospam(a)f2s.com>
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>> "eeboy" <jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote in
>>>>>>>>>> message
>>>>>>>>>> news:woydnU4jer8kwz_WnZ2dnUVZ_oadnZ2d(a)giganews.com...
>>>>>>>>>> <snip>
>>>>>>>>>>> Spent a day playing around with the optics which yielded no major
>>>>>>>>>>> improvements. The only thing I was unable to try was the optical
>>>>>>>>>>> filter
>>>>>>>>>>> (as
>>>>>>>>>>> I don't have anything suitable on hand). So, while I wait to get
>>>>>>>>>>> my hands
>>>>>>>>>>> on something I thought I'd try a few of the other suggestions... if
>>>>>>>>>>> nothing
>>>>>>>>>>> else it would be a learning experience.
>>>>>>>>>>>
>>>>>>>>>>> First I am making a change to my transmitter so that I can use a
>>>>>>>>>>> watch
>>>>>>>>>>> crystal as the time base of the modulation. I've basically added
>>>>>>>>>>> a Pierce
>>>>>>>>>>> Oscillator with its output going to one input of an AND gate. The
>>>>>>>>>>> other
>>>>>>>>>>> input of the AND gate is tied back to the existing
>>>>>>>>>>> microcontroller acting
>>>>>>>>>>> as an enable. Upon enabling the signal is fed to the gate of a FET
>>>>>>>>>>> controlling the LED. Here is a snippet of the schematic...
>>>>>>>>>>> http://img717.imageshack.us/img717/8467/transmitter.jpg . I've
>>>>>>>>>>> never
>>>>>>>>>>> actually constructed a Pierce Oscillator. From what I've been
>>>>>>>>>>> reading they
>>>>>>>>>>> may be a bit tough to get going with a buffered inverter (my
>>>>>>>>>>> case). My
>>>>>>>>>>> values were derived based on the crystal manufacturers load
>>>>>>>>>>> capacitance of
>>>>>>>>>>> 12.5pF. Comments?
>>>>>>>>>> <snip>
>>>>>>>>>>
>>>>>>>>>> As an aside, if you're bandpass filtering 32KHz, could you use a
>>>>>>>>>> large
>>>>>>>>>> capacitor from the junction of the resistor and LED to ground,
>>>>>>>>>> such that
>>>>>>>>>> when the FET turns on you get a high powered shorter spike? It
>>>>>>>>>> seems you
>>>>>>>>>> can't drive more than about 200mA with the LED shown as it's a 50/50
>>>>>>>>>> waveform. You're allowed up to 2A though with a 10us pulse. If your
>>>>>>>>>> photodiode can respond fast enough to that shorter pulse it might
>>>>>>>>>> mean you
>>>>>>>>>> can turn the gain of the receiver down and reduce background noise
>>>>>>>>>> effects.
>>>>>>>>>> You'd need to do a fourier analysis of the 50/50 waveform at lower
>>>>>>>>>> power for
>>>>>>>>>> the 32KHz content and compare to the 32KHz content of a shorter
>>>>>>>>>> pulse but at
>>>>>>>>>> higher power. Alternatively use a monostable to create a
>>>>>>>>>> controlled pulse
>>>>>>>>>> width and up the current. I'm curious whether that would work or
>>>>>>>>>> not...
>>>>>>>>>>
>>>>>>>>>> Mark.
>>>>>>>>>>
>>>>>>>>> First OP would need a battery that can deliver the current pulses,
>>>>>>>>> cr2032 cannot.
>>>>>>>> So put a capacitor across the battery[1] and it will supply the
>>>>>>>> current spike
>>>>>>>> to LED. Duty cycle can be very low for LED drive, as it's the peak
>>>>>>>> signal power
>>>>>>>> that provides contrast (signal) at the receiver, not average power
>>>>>>>> that gets
>>>>>>>> swamped by ambient light.
>>>>>>>>
>>>>>>>> If there's room you could stack a couple coin batteries for 6V to
>>>>>>>> get more LED
>>>>>>>> peak current from cap. Or, perhaps a voltage double charging the
>>>>>>>> capacitor?
>>>>>>>> Lots of options.
>>>>>>>>
>>>>>>>> [1] you might want to disconnect capacitor in between message
>>>>>>>> sequences to
>>>>>>>> improve battery life.
>>>>>>>>
>>>>>>>> Grant.
>>>>>>> Yes, I was thinking of something like putting a large cap (seveal
>>>>>>> hundred uF or larger) with a small series resistor just to limit the
>>>>>>> pulse curent and connecting it to the resistor/diode juction of the
>>>>>>> schematic posted:
>>>>>>> http://img717.imageshack.us/img717/8467/transmitter.jpg
>>>>>>>
>>>>> Make sure the capacitor has low enough ESR, else it might limit your
>>>>> pulse amplitude to some unknown value. Also, measure the voltage dip on
>>>>> the supply rail because if too deep you crystal oscillator might choke.
>>>>>
>>>>>
>>>>>>> The receiver photodiode has to be fast enough to respond to that
>>>>>>> small pulse. After that you could filter out the 32kHz, but the gain
>>>>>>> of that stage may not need to be as high so background noise is
>>>>>>> reduced.
>>>>>>>
>>>>> Photodiodes are plenty fast if the connected electronics are. You should
>>>>> have no gain at all at DC, this is very important. Not even in the first
>>>>> TIA stage.
>>>> I don't agree at all. Having low gain at DC is fine, to avoid
>>>> saturation, but if you have zero dc gain you can't tell whether you have
>>>> no signal or a hardware failure.
>>>>
>>> Well, for diagnostics you can let a wee bit of DC sneak past or provide
>>> a FET that breaks the inductive path during a test.
>>>
>>> Now I don't want to be facetious here but: You mentioned the shot noise
>>> pollution. Wouldn't that present enough signal to ascertain that the
>>> photodiode is working? I can't imagine it dropping to zilch even at
>>> night. If there was a full lunar eclipse maybe but then your DC level
>>> would also drop to zero.
>>>
>>>
>>>> But the big problem is nearly always noise--shot noise of sunlight or
>>>> differentiated amplifier voltage noise.
>>>>
>>> Ok, true, but we'd have to quantify that. I have seen IR comms (with
>>> much more data rate than here) work clear across a soccer field in
>>> Europe. Now I don't have a clue about soccer and field size, but it sure
>>> was huge.
>>
>> In one of the referenced articles upthread they were bouncing signals off
>> the clouds, but they moved up to red to avoid the water absorption of the
>> IR.
>>
>
>Yeah, it probably wouldn't be so great in a thick London fog. Unless you
>have enough energy to vaporize the water content :-)

Um, after you "vaporize the water content", what are you proposing to reflect
the light off of? ;-)
From: Martin Brown on 22 Mar 2010 04:21
Joerg wrote:
> Jon Kirwan wrote:
>> On Sun, 21 Mar 2010 14:06:38 -0700, Joerg
>> <invalid(a)invalid.invalid> wrote:
>>
>>> <snip>
>>>> But the big problem is nearly always noise--shot noise of sunlight
>>>> or differentiated amplifier voltage noise.
>>> Ok, true, but we'd have to quantify that. I have seen IR comms (with
>>> much more data rate than here) work clear across a soccer field in
>>> Europe. Now I don't have a clue about soccer and field size, but it
>>> sure was huge.
>>
>> Baffled telecopic optics, optically narrow-band filtered,
>> polarized, ...
>
> Nope, nope, and nope.

ISTR that in the mid 70's not long after cheap LEDs came available
someone published a way to do moderate range communications on a light
beam using amateur astronomical telescopes in the 3-10" range that would
work in daylight. Transmitter at placed prime focus of a 3" refractor
and the reciever at the prime focus of a 10" Newtonian reflector.

Closed tube scopes with diffraction limited optics and the larger
aperture at the receiver. Next time I see one of the group I knew who
did it I will ask if they can recall the details.

I think it was written up in Sky & Telescope. Electronics wasn't much
more fancy than a faster version of Dalek voice AM modulation on a
carrier wave (over) driving a LED and a matched detector at the focus of
a large scope. Good enough to cover one hill to the next if a bit
crackly in the days before mobile phones.

>> ... and operating at a crystal-controlled narrow band
>> modulation rate that was tightly band-passed at the receiver?
>
> Yes, there was a filter but not super fancy. Somewhat matched to the
> data rate but the shape factor was nothing to write home about, simple
> LC circuitry on the cheap.

ISTR pretty basic amateur electronics and 70's era red LEDs - may even
have been published in Everyday Practical Electronics in the UK.
Filtering was nothing more fancy than Wratten 25 red.

Pretty sure it was in the visible red too as they needed to manually
focus the beam onto the sensor to get enough signal.

Regards,
Martin Brown
From: Joerg on 22 Mar 2010 09:48
krw(a)att.bizzzzzzzzzzzz wrote:
> On Sun, 21 Mar 2010 16:48:02 -0700, Joerg <invalid(a)invalid.invalid> wrote:
>
>> Grant wrote:
>>> On Sun, 21 Mar 2010 14:06:38 -0700, Joerg <invalid(a)invalid.invalid> wrote:
>>>
>>>> Phil Hobbs wrote:
>>>>> On 3/19/2010 11:50 AM, Joerg wrote:
>>>>>> markp wrote:
>>>>>>> "markp" <map.nospam(a)f2s.com> wrote in message
>>>>>>> news:80h62eF4g7U1(a)mid.individual.net...
>>>>>>>> "Grant" <omg(a)grrr.id.au> wrote in message
>>>>>>>> news:2an6q5le2ev2v7o81mqanp9ua14jqu7s5h(a)4ax.com...
>>>>>>>>> On Fri, 19 Mar 2010 03:14:04 -0700,
>>>>>>>>> "JosephKK"<quiettechblue(a)yahoo.com> wrote:
>>>>>>>>>
>>>>>>>>>> On Thu, 18 Mar 2010 18:17:19 -0000, "markp" <map.nospam(a)f2s.com>
>>>>>>>>>> wrote:
>>>>>>>>>>
>>>>>>>>>>> "eeboy" <jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote in
>>>>>>>>>>> message
>>>>>>>>>>> news:woydnU4jer8kwz_WnZ2dnUVZ_oadnZ2d(a)giganews.com...
>>>>>>>>>>> <snip>
>>>>>>>>>>>> Spent a day playing around with the optics which yielded no major
>>>>>>>>>>>> improvements. The only thing I was unable to try was the optical
>>>>>>>>>>>> filter
>>>>>>>>>>>> (as
>>>>>>>>>>>> I don't have anything suitable on hand). So, while I wait to get
>>>>>>>>>>>> my hands
>>>>>>>>>>>> on something I thought I'd try a few of the other suggestions... if
>>>>>>>>>>>> nothing
>>>>>>>>>>>> else it would be a learning experience.
>>>>>>>>>>>>
>>>>>>>>>>>> First I am making a change to my transmitter so that I can use a
>>>>>>>>>>>> watch
>>>>>>>>>>>> crystal as the time base of the modulation. I've basically added
>>>>>>>>>>>> a Pierce
>>>>>>>>>>>> Oscillator with its output going to one input of an AND gate. The
>>>>>>>>>>>> other
>>>>>>>>>>>> input of the AND gate is tied back to the existing
>>>>>>>>>>>> microcontroller acting
>>>>>>>>>>>> as an enable. Upon enabling the signal is fed to the gate of a FET
>>>>>>>>>>>> controlling the LED. Here is a snippet of the schematic...
>>>>>>>>>>>> http://img717.imageshack.us/img717/8467/transmitter.jpg . I've
>>>>>>>>>>>> never
>>>>>>>>>>>> actually constructed a Pierce Oscillator. From what I've been
>>>>>>>>>>>> reading they
>>>>>>>>>>>> may be a bit tough to get going with a buffered inverter (my
>>>>>>>>>>>> case). My
>>>>>>>>>>>> values were derived based on the crystal manufacturers load
>>>>>>>>>>>> capacitance of
>>>>>>>>>>>> 12.5pF. Comments?
>>>>>>>>>>> <snip>
>>>>>>>>>>>
>>>>>>>>>>> As an aside, if you're bandpass filtering 32KHz, could you use a
>>>>>>>>>>> large
>>>>>>>>>>> capacitor from the junction of the resistor and LED to ground,
>>>>>>>>>>> such that
>>>>>>>>>>> when the FET turns on you get a high powered shorter spike? It
>>>>>>>>>>> seems you
>>>>>>>>>>> can't drive more than about 200mA with the LED shown as it's a 50/50
>>>>>>>>>>> waveform. You're allowed up to 2A though with a 10us pulse. If your
>>>>>>>>>>> photodiode can respond fast enough to that shorter pulse it might
>>>>>>>>>>> mean you
>>>>>>>>>>> can turn the gain of the receiver down and reduce background noise
>>>>>>>>>>> effects.
>>>>>>>>>>> You'd need to do a fourier analysis of the 50/50 waveform at lower
>>>>>>>>>>> power for
>>>>>>>>>>> the 32KHz content and compare to the 32KHz content of a shorter
>>>>>>>>>>> pulse but at
>>>>>>>>>>> higher power. Alternatively use a monostable to create a
>>>>>>>>>>> controlled pulse
>>>>>>>>>>> width and up the current. I'm curious whether that would work or
>>>>>>>>>>> not...
>>>>>>>>>>>
>>>>>>>>>>> Mark.
>>>>>>>>>>>
>>>>>>>>>> First OP would need a battery that can deliver the current pulses,
>>>>>>>>>> cr2032 cannot.
>>>>>>>>> So put a capacitor across the battery[1] and it will supply the
>>>>>>>>> current spike
>>>>>>>>> to LED. Duty cycle can be very low for LED drive, as it's the peak
>>>>>>>>> signal power
>>>>>>>>> that provides contrast (signal) at the receiver, not average power
>>>>>>>>> that gets
>>>>>>>>> swamped by ambient light.
>>>>>>>>>
>>>>>>>>> If there's room you could stack a couple coin batteries for 6V to
>>>>>>>>> get more LED
>>>>>>>>> peak current from cap. Or, perhaps a voltage double charging the
>>>>>>>>> capacitor?
>>>>>>>>> Lots of options.
>>>>>>>>>
>>>>>>>>> [1] you might want to disconnect capacitor in between message
>>>>>>>>> sequences to
>>>>>>>>> improve battery life.
>>>>>>>>>
>>>>>>>>> Grant.
>>>>>>>> Yes, I was thinking of something like putting a large cap (seveal
>>>>>>>> hundred uF or larger) with a small series resistor just to limit the
>>>>>>>> pulse curent and connecting it to the resistor/diode juction of the
>>>>>>>> schematic posted:
>>>>>>>> http://img717.imageshack.us/img717/8467/transmitter.jpg
>>>>>>>>
>>>>>> Make sure the capacitor has low enough ESR, else it might limit your
>>>>>> pulse amplitude to some unknown value. Also, measure the voltage dip on
>>>>>> the supply rail because if too deep you crystal oscillator might choke.
>>>>>>
>>>>>>
>>>>>>>> The receiver photodiode has to be fast enough to respond to that
>>>>>>>> small pulse. After that you could filter out the 32kHz, but the gain
>>>>>>>> of that stage may not need to be as high so background noise is
>>>>>>>> reduced.
>>>>>>>>
>>>>>> Photodiodes are plenty fast if the connected electronics are. You should
>>>>>> have no gain at all at DC, this is very important. Not even in the first
>>>>>> TIA stage.
>>>>> I don't agree at all. Having low gain at DC is fine, to avoid
>>>>> saturation, but if you have zero dc gain you can't tell whether you have
>>>>> no signal or a hardware failure.
>>>>>
>>>> Well, for diagnostics you can let a wee bit of DC sneak past or provide
>>>> a FET that breaks the inductive path during a test.
>>>>
>>>> Now I don't want to be facetious here but: You mentioned the shot noise
>>>> pollution. Wouldn't that present enough signal to ascertain that the
>>>> photodiode is working? I can't imagine it dropping to zilch even at
>>>> night. If there was a full lunar eclipse maybe but then your DC level
>>>> would also drop to zero.
>>>>
>>>>
>>>>> But the big problem is nearly always noise--shot noise of sunlight or
>>>>> differentiated amplifier voltage noise.
>>>>>
>>>> Ok, true, but we'd have to quantify that. I have seen IR comms (with
>>>> much more data rate than here) work clear across a soccer field in
>>>> Europe. Now I don't have a clue about soccer and field size, but it sure
>>>> was huge.
>>> In one of the referenced articles upthread they were bouncing signals off
>>> the clouds, but they moved up to red to avoid the water absorption of the
>>> IR.
>>>
>> Yeah, it probably wouldn't be so great in a thick London fog. Unless you
>> have enough energy to vaporize the water content :-)
>
> Um, after you "vaporize the water content", what are you proposing to reflect
> the light off of? ;-)


The moon? That's what ham radio folks do with EME transmission :-)

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
From: krw on 22 Mar 2010 18:37
On Mon, 22 Mar 2010 06:48:17 -0700, Joerg <invalid(a)invalid.invalid> wrote:

>krw(a)att.bizzzzzzzzzzzz wrote:
>> On Sun, 21 Mar 2010 16:48:02 -0700, Joerg <invalid(a)invalid.invalid> wrote:
>>
>>> Grant wrote:
>>>> On Sun, 21 Mar 2010 14:06:38 -0700, Joerg <invalid(a)invalid.invalid> wrote:
>>>>
>>>>> Phil Hobbs wrote:
>>>>>> On 3/19/2010 11:50 AM, Joerg wrote:
>>>>>>> markp wrote:
>>>>>>>> "markp" <map.nospam(a)f2s.com> wrote in message
>>>>>>>> news:80h62eF4g7U1(a)mid.individual.net...
>>>>>>>>> "Grant" <omg(a)grrr.id.au> wrote in message
>>>>>>>>> news:2an6q5le2ev2v7o81mqanp9ua14jqu7s5h(a)4ax.com...
>>>>>>>>>> On Fri, 19 Mar 2010 03:14:04 -0700,
>>>>>>>>>> "JosephKK"<quiettechblue(a)yahoo.com> wrote:
>>>>>>>>>>
>>>>>>>>>>> On Thu, 18 Mar 2010 18:17:19 -0000, "markp" <map.nospam(a)f2s.com>
>>>>>>>>>>> wrote:
>>>>>>>>>>>
>>>>>>>>>>>> "eeboy" <jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote in
>>>>>>>>>>>> message
>>>>>>>>>>>> news:woydnU4jer8kwz_WnZ2dnUVZ_oadnZ2d(a)giganews.com...
>>>>>>>>>>>> <snip>
>>>>>>>>>>>>> Spent a day playing around with the optics which yielded no major
>>>>>>>>>>>>> improvements. The only thing I was unable to try was the optical
>>>>>>>>>>>>> filter
>>>>>>>>>>>>> (as
>>>>>>>>>>>>> I don't have anything suitable on hand). So, while I wait to get
>>>>>>>>>>>>> my hands
>>>>>>>>>>>>> on something I thought I'd try a few of the other suggestions... if
>>>>>>>>>>>>> nothing
>>>>>>>>>>>>> else it would be a learning experience.
>>>>>>>>>>>>>
>>>>>>>>>>>>> First I am making a change to my transmitter so that I can use a
>>>>>>>>>>>>> watch
>>>>>>>>>>>>> crystal as the time base of the modulation. I've basically added
>>>>>>>>>>>>> a Pierce
>>>>>>>>>>>>> Oscillator with its output going to one input of an AND gate. The
>>>>>>>>>>>>> other
>>>>>>>>>>>>> input of the AND gate is tied back to the existing
>>>>>>>>>>>>> microcontroller acting
>>>>>>>>>>>>> as an enable. Upon enabling the signal is fed to the gate of a FET
>>>>>>>>>>>>> controlling the LED. Here is a snippet of the schematic...
>>>>>>>>>>>>> http://img717.imageshack.us/img717/8467/transmitter.jpg . I've
>>>>>>>>>>>>> never
>>>>>>>>>>>>> actually constructed a Pierce Oscillator. From what I've been
>>>>>>>>>>>>> reading they
>>>>>>>>>>>>> may be a bit tough to get going with a buffered inverter (my
>>>>>>>>>>>>> case). My
>>>>>>>>>>>>> values were derived based on the crystal manufacturers load
>>>>>>>>>>>>> capacitance of
>>>>>>>>>>>>> 12.5pF. Comments?
>>>>>>>>>>>> <snip>
>>>>>>>>>>>>
>>>>>>>>>>>> As an aside, if you're bandpass filtering 32KHz, could you use a
>>>>>>>>>>>> large
>>>>>>>>>>>> capacitor from the junction of the resistor and LED to ground,
>>>>>>>>>>>> such that
>>>>>>>>>>>> when the FET turns on you get a high powered shorter spike? It
>>>>>>>>>>>> seems you
>>>>>>>>>>>> can't drive more than about 200mA with the LED shown as it's a 50/50
>>>>>>>>>>>> waveform. You're allowed up to 2A though with a 10us pulse. If your
>>>>>>>>>>>> photodiode can respond fast enough to that shorter pulse it might
>>>>>>>>>>>> mean you
>>>>>>>>>>>> can turn the gain of the receiver down and reduce background noise
>>>>>>>>>>>> effects.
>>>>>>>>>>>> You'd need to do a fourier analysis of the 50/50 waveform at lower
>>>>>>>>>>>> power for
>>>>>>>>>>>> the 32KHz content and compare to the 32KHz content of a shorter
>>>>>>>>>>>> pulse but at
>>>>>>>>>>>> higher power. Alternatively use a monostable to create a
>>>>>>>>>>>> controlled pulse
>>>>>>>>>>>> width and up the current. I'm curious whether that would work or
>>>>>>>>>>>> not...
>>>>>>>>>>>>
>>>>>>>>>>>> Mark.
>>>>>>>>>>>>
>>>>>>>>>>> First OP would need a battery that can deliver the current pulses,
>>>>>>>>>>> cr2032 cannot.
>>>>>>>>>> So put a capacitor across the battery[1] and it will supply the
>>>>>>>>>> current spike
>>>>>>>>>> to LED. Duty cycle can be very low for LED drive, as it's the peak
>>>>>>>>>> signal power
>>>>>>>>>> that provides contrast (signal) at the receiver, not average power
>>>>>>>>>> that gets
>>>>>>>>>> swamped by ambient light.
>>>>>>>>>>
>>>>>>>>>> If there's room you could stack a couple coin batteries for 6V to
>>>>>>>>>> get more LED
>>>>>>>>>> peak current from cap. Or, perhaps a voltage double charging the
>>>>>>>>>> capacitor?
>>>>>>>>>> Lots of options.
>>>>>>>>>>
>>>>>>>>>> [1] you might want to disconnect capacitor in between message
>>>>>>>>>> sequences to
>>>>>>>>>> improve battery life.
>>>>>>>>>>
>>>>>>>>>> Grant.
>>>>>>>>> Yes, I was thinking of something like putting a large cap (seveal
>>>>>>>>> hundred uF or larger) with a small series resistor just to limit the
>>>>>>>>> pulse curent and connecting it to the resistor/diode juction of the
>>>>>>>>> schematic posted:
>>>>>>>>> http://img717.imageshack.us/img717/8467/transmitter.jpg
>>>>>>>>>
>>>>>>> Make sure the capacitor has low enough ESR, else it might limit your
>>>>>>> pulse amplitude to some unknown value. Also, measure the voltage dip on
>>>>>>> the supply rail because if too deep you crystal oscillator might choke.
>>>>>>>
>>>>>>>
>>>>>>>>> The receiver photodiode has to be fast enough to respond to that
>>>>>>>>> small pulse. After that you could filter out the 32kHz, but the gain
>>>>>>>>> of that stage may not need to be as high so background noise is
>>>>>>>>> reduced.
>>>>>>>>>
>>>>>>> Photodiodes are plenty fast if the connected electronics are. You should
>>>>>>> have no gain at all at DC, this is very important. Not even in the first
>>>>>>> TIA stage.
>>>>>> I don't agree at all. Having low gain at DC is fine, to avoid
>>>>>> saturation, but if you have zero dc gain you can't tell whether you have
>>>>>> no signal or a hardware failure.
>>>>>>
>>>>> Well, for diagnostics you can let a wee bit of DC sneak past or provide
>>>>> a FET that breaks the inductive path during a test.
>>>>>
>>>>> Now I don't want to be facetious here but: You mentioned the shot noise
>>>>> pollution. Wouldn't that present enough signal to ascertain that the
>>>>> photodiode is working? I can't imagine it dropping to zilch even at
>>>>> night. If there was a full lunar eclipse maybe but then your DC level
>>>>> would also drop to zero.
>>>>>
>>>>>
>>>>>> But the big problem is nearly always noise--shot noise of sunlight or
>>>>>> differentiated amplifier voltage noise.
>>>>>>
>>>>> Ok, true, but we'd have to quantify that. I have seen IR comms (with
>>>>> much more data rate than here) work clear across a soccer field in
>>>>> Europe. Now I don't have a clue about soccer and field size, but it sure
>>>>> was huge.
>>>> In one of the referenced articles upthread they were bouncing signals off
>>>> the clouds, but they moved up to red to avoid the water absorption of the
>>>> IR.
>>>>
>>> Yeah, it probably wouldn't be so great in a thick London fog. Unless you
>>> have enough energy to vaporize the water content :-)
>>
>> Um, after you "vaporize the water content", what are you proposing to reflect
>> the light off of? ;-)
>
>
>The moon? That's what ham radio folks do with EME transmission :-)

I guess that works for half the day. The 1/r^2 is rather extreme, though.
From: JosephKK on 23 Mar 2010 00:59
On Mon, 22 Mar 2010 17:37:50 -0500, "krw(a)att.bizzzzzzzzzzzz" <krw(a)att.bizzzzzzzzzzzz> wrote:

>On Mon, 22 Mar 2010 06:48:17 -0700, Joerg <invalid(a)invalid.invalid> wrote:
>
>>krw(a)att.bizzzzzzzzzzzz wrote:
>>> On Sun, 21 Mar 2010 16:48:02 -0700, Joerg <invalid(a)invalid.invalid> wrote:
>>>
<snip>
>>>
>>> Um, after you "vaporize the water content", what are you proposing to reflect
>>> the light off of? ;-)
>>
>>
>>The moon? That's what ham radio folks do with EME transmission :-)
>
>I guess that works for half the day. The 1/r^2 is rather extreme, though.

Yep. Hams use very sensitive receivers and very high gain antennas 35 dB and up.
Though getting much past 44 dBi is rather difficult IIRC.
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Prev: Microeconomics 5e Jeffrey M. Perloff test bank and solution manual is available for purchase at affordable prices. Contact me at alltestbanks11[at]gmail.com to buy it today.
Next: Essentials of the Legal Environment 2nd Edition 2008 Roger LeRoy Miller Test bank is available for purchase at affordable prices. Contact me at alltestbanks11[at]gmail.com to buy it today.