Remote IR on-off switch
in [Design]
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From: pimpom on 17 Feb 2010 02:38 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.
From: John O'Flaherty on 17 Feb 2010 10:34 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? > 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. -- John
From: Glenn Gundlach on 17 Feb 2010 11:01 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. G²
From: pimpom on 17 Feb 2010 11:39 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. > >> 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.
From: Jim Thompson on 17 Feb 2010 11:44
On Wed, 17 Feb 2010 22:09:02 +0530, "pimpom" <pimpom(a)invalid.invalid> wrote: [snip] > 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. > You are correct. ...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. |