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From: pimpom on 17 Feb 2010 11:49
Glenn Gundlach wrote:
> On Feb 16, 11:38 pm, "pimpom" <pim...(a)invalid.invalid> wrote:
>> I've come across this DIY IR remote on-off switch design more
>> than once with only minor
>> variations.http://img109.imageshack.us/img109/6399/irswitch.png
>>
>> It looked OK at first, but then it seemed to me that R3 and D1
>> are not really needed. Why not just omit R3 and short out D1
>> as
>> on the right side of image?
>>
>> And is such heavy filtering necessary? I'd think 38kHz pulses
>> fired in ~1kHz bursts would be adequately filtered with a much
>> lower RC combination and will have faster response too.
>
> Or you could add a pair of uProcs and trasnmit specific codes
> which
> would make it much more robust. I couln't get the Freescale
> 68HC908
> series to modulate 38KHz directly - possibly a lack of
> programming
> skills on my part but with a little added glue logic it works
> fine.
> Receiving is not at all difficult. TV remotes (Samsung and Sony
> for
> certain) transmit 32 bits total with mirrored 8 bit blocks.
> It's
> pretty reliable. You can do it too if it's important.
>

Thanks for your interest. It's not that I want to build this
design. I'm using a different approach in something I _am_
building. It's just that I came across this circuit and the
inclusion of R3 and D1, while apparently logical at first, seems
superfluous on closer inspection. Please also read my reply to
John O'Flaherty.


From: John O'Flaherty on 17 Feb 2010 12:03
On Wed, 17 Feb 2010 22:09:02 +0530, "pimpom" <pimpom(a)invalid.invalid>
wrote:

>John O'Flaherty wrote:
>> On Wed, 17 Feb 2010 13:08:43 +0530, "pimpom"
>> <pimpom(a)invalid.invalid>
>> wrote:
>>
>>> I've come across this DIY IR remote on-off switch design more
>>> than once with only minor variations.
>>> http://img109.imageshack.us/img109/6399/irswitch.png
>>>
>>> It looked OK at first, but then it seemed to me that R3 and D1
>>> are not really needed. Why not just omit R3 and short out D1
>>> as
>>> on the right side of image?
>>>
>>> And is such heavy filtering necessary? I'd think 38kHz pulses
>>> fired in ~1kHz bursts
>>
>> Do you mean burst of 1000 cycles, or about 25 ms at 38 kHz?
>
>No. Datasheets indicate that, for noise suppression, most IR
>receiver modules are optimised to receive 38kHz pulses in bursts
>roughly 0.5 msec on, 0.5msec off. This is where I derived the
>~1kHz figure from.

I see what you meant, now.

>>> would be adequately filtered with a much
>>> lower RC combination and will have faster response too.
>>
>> The 4013 changes state on a positive clock, or after about 13
>> ms (27k
>> and 0.47 uF). The discharge time constant prevents retriggering
>> for
>> about 1/2 second (1 M and 0.47 uF). Do you want it to toggle
>> faster
>> than once per second? The danger is that you could get multiple
>> pulses
>> from a buttonpush (if that's what the input is coming from) and
>> have
>> the toggle end up in a random state.
>
>I _am_ building something using an IR receiver module, but using
>another technique. It's just that I came across this circuit more
>than once and got curious about the validity of the design.
>
>I get your point about unintentional toggles. Anyway, I tossed in
>the matter of filter time constant as an afterthought. My
>attention was mainly on why the designer(s) considered it
>necessary to use R3 and D1. The pulsed output from Q1's collector
>is already unidirectional and does not need rectification. The
>collector, even without a reverse blocking diode, is essentially
>an open circuit (megohms) in the off state and will have
>negligible effect on the filter efficiency.
>

The diode gives a different time constant for discharge than for
charge. If the diode is shorted out, the 100 k collector resistor will
shorten the discharge time constant to 0.13 sec or so, by paralleling
the 1 Megohm. However, if you can get by with a 1 megohm collector
resistor, based on the transistor leakage and the IR receiver turning
the transistor fully off, it should work as you've drawn it.
--
John
From: pimpom on 17 Feb 2010 12:53
John O'Flaherty wrote:
> On Wed, 17 Feb 2010 22:09:02 +0530, "pimpom"
> <pimpom(a)invalid.invalid>
> wrote:
>
>> John O'Flaherty wrote:
>>> On Wed, 17 Feb 2010 13:08:43 +0530, "pimpom"
>>> <pimpom(a)invalid.invalid>
>>> wrote:
>>>
>>>> I've come across this DIY IR remote on-off switch design
>>>> more
>>>> than once with only minor variations.
>>>> http://img109.imageshack.us/img109/6399/irswitch.png
>>>>
>>>> It looked OK at first, but then it seemed to me that R3 and
>>>> D1
>>>> are not really needed. Why not just omit R3 and short out D1
>>>> as
>>>> on the right side of image?
>>>>
>>>
>>
>
> The diode gives a different time constant for discharge than
> for
> charge. If the diode is shorted out, the 100 k collector
> resistor will
> shorten the discharge time constant to 0.13 sec or so, by
> paralleling
> the 1 Megohm.

Omitting the 100k resistor will obviate that.

> However, if you can get by with a 1 megohm collector
> resistor, based on the transistor leakage and the IR receiver
> turning
> the transistor fully off, it should work as you've drawn it.

BC5xx transistors have very low leakage - Ices 4uA max at Tj 150
C. Actual leakage encountered in practice are probably much less
even at 150 C. And Tj in the target hobbyist use is unlikely to
exceed 50 deg C. So we can expect sub-100 nA leakage.

I haven't seen leakage figures for the output of an IR receiver
module. Anything less than 10uA will be shunted away by the 27k
paralleling b-e and won't cause Q1 to conduct.

If I were to adapt this circuit for my own use, I'd probably use
a higher capacitance for C1 (an electrolytic should be OK) and
correspondingly lower values for R4 and R5. Say 2.2uF, 4.7k and
220k respectively.


From: John O'Flaherty on 17 Feb 2010 13:11
On Wed, 17 Feb 2010 23:23:58 +0530, "pimpom" <pimpom(a)invalid.invalid>
wrote:

>John O'Flaherty wrote:
>> On Wed, 17 Feb 2010 22:09:02 +0530, "pimpom"
>> <pimpom(a)invalid.invalid>
>> wrote:
>>
>>> John O'Flaherty wrote:
>>>> On Wed, 17 Feb 2010 13:08:43 +0530, "pimpom"
>>>> <pimpom(a)invalid.invalid>
>>>> wrote:
>>>>
>>>>> I've come across this DIY IR remote on-off switch design
>>>>> more
>>>>> than once with only minor variations.
>>>>> http://img109.imageshack.us/img109/6399/irswitch.png
>>>>>
>>>>> It looked OK at first, but then it seemed to me that R3 and
>>>>> D1
>>>>> are not really needed. Why not just omit R3 and short out D1
>>>>> as
>>>>> on the right side of image?
>>>>>
>>>>
>>>
>>
>> The diode gives a different time constant for discharge than
>> for
>> charge. If the diode is shorted out, the 100 k collector
>> resistor will
>> shorten the discharge time constant to 0.13 sec or so, by
>> paralleling
>> the 1 Megohm.
>
>Omitting the 100k resistor will obviate that.

Right. I was addressing your question about the validity of the
original design. I think they wanted the collector to switch to ground
quickly and leave the discharge controlled by the 1 megohm.

>> However, if you can get by with a 1 megohm collector
>> resistor, based on the transistor leakage and the IR receiver
>> turning
>> the transistor fully off, it should work as you've drawn it.
>
>BC5xx transistors have very low leakage - Ices 4uA max at Tj 150
>C. Actual leakage encountered in practice are probably much less
>even at 150 C. And Tj in the target hobbyist use is unlikely to
>exceed 50 deg C. So we can expect sub-100 nA leakage.
>
>I haven't seen leakage figures for the output of an IR receiver
>module. Anything less than 10uA will be shunted away by the 27k
>paralleling b-e and won't cause Q1 to conduct.

I have no idea what the output circuit of that IR thing looks like,
but as long as it reaches nearly to the positive rail, it should be
fine.

>If I were to adapt this circuit for my own use, I'd probably use
>a higher capacitance for C1 (an electrolytic should be OK) and
>correspondingly lower values for R4 and R5. Say 2.2uF, 4.7k and
>220k respectively.

Makes sense.

--
John
From: Jim Thompson on 17 Feb 2010 13:17
On Wed, 17 Feb 2010 11:03:29 -0600, John O'Flaherty
<quiasmox(a)yeeha.com> wrote:

>On Wed, 17 Feb 2010 22:09:02 +0530, "pimpom" <pimpom(a)invalid.invalid>
>wrote:
>
>>John O'Flaherty wrote:
>>> On Wed, 17 Feb 2010 13:08:43 +0530, "pimpom"
>>> <pimpom(a)invalid.invalid>
>>> wrote:
>>>
>>>> I've come across this DIY IR remote on-off switch design more
>>>> than once with only minor variations.
>>>> http://img109.imageshack.us/img109/6399/irswitch.png
>>>>
>>>> It looked OK at first, but then it seemed to me that R3 and D1
>>>> are not really needed. Why not just omit R3 and short out D1
>>>> as
>>>> on the right side of image?
>>>>
>>>> And is such heavy filtering necessary? I'd think 38kHz pulses
>>>> fired in ~1kHz bursts
>>>
>>> Do you mean burst of 1000 cycles, or about 25 ms at 38 kHz?
>>
>>No. Datasheets indicate that, for noise suppression, most IR
>>receiver modules are optimised to receive 38kHz pulses in bursts
>>roughly 0.5 msec on, 0.5msec off. This is where I derived the
>>~1kHz figure from.
>
>I see what you meant, now.
>
>>>> would be adequately filtered with a much
>>>> lower RC combination and will have faster response too.
>>>
>>> The 4013 changes state on a positive clock, or after about 13
>>> ms (27k
>>> and 0.47 uF). The discharge time constant prevents retriggering
>>> for
>>> about 1/2 second (1 M and 0.47 uF). Do you want it to toggle
>>> faster
>>> than once per second? The danger is that you could get multiple
>>> pulses
>>> from a buttonpush (if that's what the input is coming from) and
>>> have
>>> the toggle end up in a random state.
>>
>>I _am_ building something using an IR receiver module, but using
>>another technique. It's just that I came across this circuit more
>>than once and got curious about the validity of the design.
>>
>>I get your point about unintentional toggles. Anyway, I tossed in
>>the matter of filter time constant as an afterthought. My
>>attention was mainly on why the designer(s) considered it
>>necessary to use R3 and D1. The pulsed output from Q1's collector
>>is already unidirectional and does not need rectification. The
>>collector, even without a reverse blocking diode, is essentially
>>an open circuit (megohms) in the off state and will have
>>negligible effect on the filter efficiency.
>>
>
>The diode gives a different time constant for discharge than for
>charge. If the diode is shorted out, the 100 k collector resistor will
>shorten the discharge time constant to 0.13 sec or so, by paralleling
>the 1 Megohm. However, if you can get by with a 1 megohm collector
>resistor, based on the transistor leakage and the IR receiver turning
>the transistor fully off, it should work as you've drawn it.

Nope. R3 isn't used in pimpom's version, as shown on the right side
of...

http://img109.imageshack.us/img109/6399/irswitch.png

...Jim Thompson
--
| James E.Thompson, CTO | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
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