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: JosephKK on 20 Mar 2010 02:42

On Fri, 19 Mar 2010 12:30:08 -0500, "eeboy" <jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote:

>>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.
>
>The battery delivers about 240mA based on the voltage which develops across
>the 1 ohm resistor. I've thought of placing the capacitor across the
>battery but that leakage current would shorten the life of the battery as
>you point out. True it could be disconnected at the cost of another
>component. Might be worth looking into...
>
>---------------------------------------
>Posted through http://www.Electronics-Related.com

The datasheets i have perused do not support that cell producing 240 mA, but
more like 240 uA. After all the total charge is on the order of 240 mAhour,
and the internal resistance seems to be over 100 ohms.

From: Grant on 20 Mar 2010 03:42

On Fri, 19 Mar 2010 23:42:55 -0700, "JosephKK"<quiettechblue(a)yahoo.com> wrote:

>On Fri, 19 Mar 2010 12:30:08 -0500, "eeboy" <jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote:
>
>>>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.
>>
>>The battery delivers about 240mA based on the voltage which develops across
>>the 1 ohm resistor. I've thought of placing the capacitor across the
>>battery but that leakage current would shorten the life of the battery as
>>you point out. True it could be disconnected at the cost of another
>>component. Might be worth looking into...
>>
>>---------------------------------------
>>Posted through http://www.Electronics-Related.com
>
>The datasheets i have perused do not support that cell producing 240 mA, but
>more like 240 uA. After all the total charge is on the order of 240 mAhour,
>and the internal resistance seems to be over 100 ohms.

They'll easily give 10mA or more on load. Product we used them in
was UHF AM tx and we used stack of two to get enough power for decent
range. I don't recall the detailed numbers as this was back in the '80s.

Grant.

From: Phil Hobbs on 21 Mar 2010 14:23

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.

But the big problem is nearly always noise--shot noise of sunlight or
differentiated amplifier voltage noise.

Cheers

Phil Hobbs

From: Joerg on 21 Mar 2010 17:06

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.

--
Regards, Joerg

http://www.analogconsultants.com/

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

From: Jon Kirwan on 21 Mar 2010 17:12

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, and operating at a crystal-controlled narrow band
modulation rate that was tightly band-passed at the receiver?

Jon