IR Receiver/Demodulator [Design]

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From: markp on 19 Mar 2010 07:43

"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

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.

Mark.

From: markp on 19 Mar 2010 08:13

"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
>
> 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.
>
> Mark.

Other possibilites for the receiver might be to use a tube, cone or even a
parabolic reflector made from IR reflective material. If you use the
reflector you'd place the receiver pointing inwards at the focal point. This
effectively produces gain as it captures power from a larger area. An IR
transmissive filter on the receiver (worthless to ad that to the
transmitter!). The LED already has a tight beam angle so no need to modify
that.

Mark.

From: Joerg on 19 Mar 2010 11:50

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.

>> Mark.
>
> Other possibilites for the receiver might be to use a tube, cone or even a
> parabolic reflector made from IR reflective material. If you use the
> reflector you'd place the receiver pointing inwards at the focal point. This
> effectively produces gain as it captures power from a larger area. An IR
> transmissive filter on the receiver (worthless to ad that to the
> transmitter!). The LED already has a tight beam angle so no need to modify
> that.
>

The tube is an absolute minimum. I don't think the scheme will work at
all during the day if the photodiode gets direct sunlight.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

From: Grant on 19 Mar 2010 11:50

On Fri, 19 Mar 2010 11:43:12 -0000, "markp" <map.nospam(a)f2s.com> wrote:

>
>"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

Bit more complex would be to use an inductor to transfer power to the IR LEDs.
See figure 2 in http://ww1.microchip.com/downloads/en/AppNotes/91062a.pdf for
a power circuit that uses 1mH to dump current into a string of four IR LEDs.
>
>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.

I found two PDs suit this: BPV23F and BPW41N both look plenty fast enough
and are filtered to cut response to visible light. For ~950nm operation.

As far as a receiver directional filter goes, there's mention of a
honeycomb type filter (I think it got a mention in one of referenced documents
upthread).

I forget the name of the beast but there's a technique used for flash
photography that uses a bunch of straws in front of the flash to limit
distribution of light to a small circle. Something like that could be
used to limit reception angle to the receiver? The shorter the straws,
the wider is the reception angle.

Grant.

From: Jim Thompson on 19 Mar 2010 12:45

On Fri, 19 Mar 2010 08:50:01 -0700, Joerg <invalid(a)invalid.invalid>
wrote:

>markp wrote:
[snip]
>>
>> Other possibilites for the receiver might be to use a tube, cone or even a
>> parabolic reflector made from IR reflective material. If you use the
>> reflector you'd place the receiver pointing inwards at the focal point. This
>> effectively produces gain as it captures power from a larger area. An IR
>> transmissive filter on the receiver (worthless to ad that to the
>> transmitter!). The LED already has a tight beam angle so no need to modify
>> that.
>>
>
>The tube is an absolute minimum. I don't think the scheme will work at
>all during the day if the photodiode gets direct sunlight.

You still may need a DC loop to get the receiver from saturating on
ambient. Here in AZ, that seems an absolute necessity.

...Jim Thompson
--
| James E.Thompson, CTO | mens |
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| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
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