IR Receiver/Demodulator [Design]

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.

From: Martin Brown on 19 Mar 2010 05:17

Joerg wrote:
> Tim Williams wrote:
>> "Joerg" <invalid(a)invalid.invalid> wrote in message
>> news:80fvvhFb78U1(a)mid.individual.net...
>>> Hey, couldn't you use that for informal energy audits, find leaks in
>>> houses?
>>
>> Only if the house is the temperature of melting lead. Room temp stuff
>> glows in the << 1eV range, nothing a silicon CCD will see.
>
> http://geektechnique.org/projectlab/254/how-to-turn-a-digital-camera-into-an-ir-camera
>
> This guy's face probably isn't more than 100F.

But it is being illuminated by the solid state IR led array he built as
a part of the project. Yes you can film in the dark with suitable
amateur kit without startling wildlife. But you are not seeing any
temperature differences unless the thing is *very* hot. You are just
seeing how well the object reflects near IR wavelengths.

Notably trees and foliage are white. If you have some near IR long pass
filter and look through it for a while (about a minute) with all other
light excluded your dark adapted eyes will see a little bit into the
near IR with a sort of odd false colour effect.

Typical imaging CCDs with their IR filter removed will go out to around
1000nm or 1um which is about an order of magnitude short of the 10um far
IR thermal band characteristic of ambient temperatures on Earth.

Regards,
Martin Brown

From: JosephKK on 19 Mar 2010 05:57

On Wed, 17 Mar 2010 11:59:24 -0500, "eeboy" <jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote:

>>Are you using the proper emitter one that is wavelength matched to you
>>TSOP?
>
>I am using a LTE-5228A which has a peak at 940nm. The data sheet on the
>TSOP part appears to have a peak at roughly the same spot.
>
>>I agree about the optics but unless your building these in large
>>quantity you likely don't have any optics.
>>
>
>I am currently using a plastic fresnel lens in front of the device.
>However, the fresnel lens is being shared with another optical component
>which has been given 'optical priority'... meaning the other component is
>at the focal point so the TSOP device sits about .25" below. I could
>probably have (and should have) pushed that device up closer to the other
>device (within .100"). Perhaps I'll run some tests where I slide the
>fresnel lens down to see if the situation
>
>>Are you hammering the LED with it's max peak current are close to it?
>>Keeping in mind max package power dissipation for your LED in the
>>worst case ambient etc..
>
>I believe I am currently driving it past the datasheet spec. My transmitter
>is powered by a CR2032. I am utilizing a 1 ohm resistor in the path which
>theoretically results in a 1.8A current for up to 80ms. The datasheets
>states the maximum as 2A for 10uS. However, I am certain the small 7mil
>trace width on the transmitter PCB add a good bit of resistance to the path
>as well.
>
Well, due to the nature of the cell you will be lucky to get much more than
2 mA out of that cell. Unless you have a huge capacitor across the cell you
are not getting anything like the output you expect.
>>
>>You can adjust the duty cycle to keep the average current to
>>acceptable limits. Like 10% for the carrier modulated at 40% for
>>continuous transmission at 1A pulses this would be about 40mA average
>>current. You could reduce this further by using discontinuous
>>transmission i.e transmit intermittently in bursts .
>>
>
>I am utilizing a 50% duty cycle. I had no idea I could get away with that.
>Definitely going to adjust the duty cycle downward.
>
>---------------------------------------
>Posted through http://www.Electronics-Related.com

From: JosephKK on 19 Mar 2010 06:14

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.

From: markp on 19 Mar 2010 07:19

"JosephKK" <quiettechblue(a)yahoo.com> wrote in message
news:nhj6q5pmo80u528u70f27u4b8sv50lmgkg(a)4ax.com...
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.

True, but a capacitor can. The CR2032 would only be topping up the capacitor
at relatively low current (depending on mark/space ratio). I've no idea
whether this would work though in practice.

Mark.

From: Grant on 19 Mar 2010 07:25

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.