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From: pimpom on 17 Feb 2010 13:57
John O'Flaherty wrote:
> On Wed, 17 Feb 2010 23:23:58 +0530, "pimpom"
> <pimpom(a)invalid.invalid>
> wrote:
>
>>
>> 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.

Block diagrams on manufacturers' datasheets usually give the
output as the collector of an NPN BJT, like the output of popular
comparators but with a 20-30K internal resistor to Vcc. This is
probably meant to enable driving the base of an external NPN BJT
without any external component.


From: John Fields on 17 Feb 2010 16:56
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?

---
Even better: (View in Courier)

+5
|
+-----+-----------+
| | |
| [10k] |
| | E
| +--[10k]--B PNP
| | C
[IRRX]---+ |
| | +-----+---->4013 CLK
| | | |
| | [470nF] [1M]
| | | |
+-----+-----------+-----+
|
GND

That way the cap would charge up very quickly and discharge slowly,
making an excellent debouncer for the 4013's clock.

Also, I like the idea of driving the base into saturation through a
single resistor pulled down to ground rather than through a voltage
divider.
---

>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.

---
The circuit is most likely activated by a push-button controlled CW
infrared transmitter, so there'd be no modulation, and no need for a
filter other than that required to debounce the signal into the 4013's
clock.

JF
From: Spehro Pefhany on 17 Feb 2010 17:11
On Wed, 17 Feb 2010 15:56:17 -0600, John Fields
<jfields(a)austininstruments.com> 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?
>
>---
>Even better: (View in Courier)
>
> +5
> |
> +-----+-----------+
> | | |
> | [10k] |
> | | E
> | +--[10k]--B PNP
> | | C
> [IRRX]---+ |
> | | +-----+---->4013 CLK
> | | | |
> | | [470nF] [1M]
> | | | |
> +-----+-----------+-----+
> |
> GND
>
>That way the cap would charge up very quickly and discharge slowly,
>making an excellent debouncer for the 4013's clock.

CD4013 does not have a ST input on the clock, and that will violate
the max clock rise/fall times. Would be okay with a HC14 or other ST
gate before the clock input.

From: John Fields on 17 Feb 2010 17:03
On Thu, 18 Feb 2010 00:27:49 +0530, "pimpom" <pimpom(a)invalid.invalid>
wrote:

>John O'Flaherty wrote:
>> On Wed, 17 Feb 2010 23:23:58 +0530, "pimpom"
>> <pimpom(a)invalid.invalid>
>> wrote:
>>
>>>
>>> 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.
>
>Block diagrams on manufacturers' datasheets usually give the
>output as the collector of an NPN BJT, like the output of popular
>comparators but with a 20-30K internal resistor to Vcc. This is
>probably meant to enable driving the base of an external NPN BJT
>without any external component.

---
Or a PNP with a single external resistor.

JF
From: John Fields on 17 Feb 2010 17:39
On Wed, 17 Feb 2010 17:11:37 -0500, Spehro Pefhany
<speffSNIP(a)interlogDOTyou.knowwhat> wrote:

>On Wed, 17 Feb 2010 15:56:17 -0600, John Fields
><jfields(a)austininstruments.com> 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?
>>
>>---
>>Even better: (View in Courier)
>>
>> +5
>> |
>> +-----+-----------+
>> | | |
>> | [10k] |
>> | | E
>> | +--[10k]--B PNP
>> | | C
>> [IRRX]---+ |
>> | | +-----+---->4013 CLK
>> | | | |
>> | | [470nF] [1M]
>> | | | |
>> +-----+-----------+-----+
>> |
>> GND
>>
>>That way the cap would charge up very quickly and discharge slowly,
>>making an excellent debouncer for the 4013's clock.
>
>CD4013 does not have a ST input on the clock, and that will violate
>the max clock rise/fall times. Would be okay with a HC14 or other ST
>gate before the clock input.

---
Yup, good catch.

Thanks. :-)

JF
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