Problem with IR detection.
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From: John Fields on 8 Apr 2010 10:12 On Thu, 8 Apr 2010 14:14:07 +0530, "pimpom" <pimpom(a)invalid.invalid> wrote: >I'm not using a readymade transmitter. I made my own using a >38kHz carrier, switched on and off in bursts. I started out with >about 500usec on, 450usec off. When that didn't work (the >received waveform appears briefly and then disappears), I varied >the on-off periods between 300 and 800 usec. No difference. The >receiver works with my TV remote control. --- If it works with the remote control, then I suspect that what's wrong is that your transmitter carrier frequency is off-frequency just enough to give you glitch outputs from the receiver. why not try monitoring the output of your receiver while adjusting the CW transmitter carrier frequency until you get a solid output from the receiver? Diddle the TX freq control back and forth to find the edges of the receiver's passband and then set the control midpoint between them. Also, make sure that the output of your receiver is properly pulled up to Vcc if it doesn't have a totem-pole output, and make sure it's DC coupled into whatever it's supposed to be driving. JF
From: Frnak McKenney on 8 Apr 2010 12:50 On Thu, 8 Apr 2010 14:14:07 +0530, pimpom <pimpom(a)invalid.invalid> wrote: > TTman wrote: >> "pimpom" <pimpom(a)invalid.invalid> wrote in message >> news:hpjlfd$8dn$1(a)news.albasani.net... >>> I'm trying to devise a presence detector using an IR beam and >>> a standard remote control IR receiver module. I couldn't find >>> datasheets for the receiver modules I can find locally and >>> proceeded on the assumption that they'd be similar to the >>> ones for which I have datasheets, like the Vishay, Sharp and >>> Panasonic types. >>> >>> To minimize interference from unwanted radiation sources, the >>> known types all set limitations on burst length, gap time and >>> maximum number of bursts per second, and I made a note of >>> those. But I cannot get the system working properly. I get >>> detection briefly when the beam is unblocked and I get the >>> expected waveforms at the receiver output, but the signal then >>> dies down quickly. I've tried varying the burst length from >>> 300-800usec with corresponding gap times. [...] > I'm not using a readymade transmitter. I made my own using a > 38kHz carrier, switched on and off in bursts. I started out with > about 500usec on, 450usec off. When that didn't work (the > received waveform appears briefly and then disappears), I varied > the on-off periods between 300 and 800 usec. No difference. The > receiver works with my TV remote control. Not all IR remote control receivers are alike; some a more equalizing than others. <grin> The remote control coding patterns do fall into groups, but many (all?) receivers are optimized to receive particular patterns or groups of patterns, as well as for various kinds of "noise". To add to the fun, a sufficiently strong source of IR-or-close light will overwhelm the receiver just as a sufficiently loud noise can make it impossible to hear someone speaking to you. Bright sunlight is a real nasty, for example. Vishay, in a four-page PDF file titled "Data Formats for IR Remote Control", describes some of the types of patterns used. On the last page it provides a compatibility cross-reference for its modules, which depends not only on the IR carrier frequency matching but also on the kind of AGC (automatic gain control) algorithm implemented. AGC is a wonderful thing, since it allows the receiver to adjust it own gain based on what it considers the incoming signal vs. everything else ("noise"), but if it makes the wrong asumptions it may crank its gain into overload, or effectively shut itself off. The problem you describe (works initially, then fades out) sounds like a case of mis-adapting AGC. If you haven't already seen the Vishay document, you might take a look at it. If nothing else, it will give you some idea of what you might be up against working with an unknown IR receiver. http://www.vishay.com/docs/80071/dataform.pdf Hope this helps... Frank McKenney -- Knowledge does not necessarily imply judgment. All truly critical, as against technical, argument is either intuitive or hypothetical or partial. This cannot be compensated for by a study of the raw material, however exhaustive. -- Robert Conquest, "The Dragons of Expectation" -- Frank McKenney, McKenney Associates Richmond, Virginia / (804) 320-4887 Munged E-mail: frank uscore mckenney ayut mined spring dawt cahm (y'all)
From: pimpom on 8 Apr 2010 15:25 John Fields wrote: > On Thu, 8 Apr 2010 14:14:07 +0530, "pimpom" > <pimpom(a)invalid.invalid> > wrote: > > >> I'm not using a readymade transmitter. I made my own using a >> 38kHz carrier, switched on and off in bursts. I started out >> with >> about 500usec on, 450usec off. When that didn't work (the >> received waveform appears briefly and then disappears), I >> varied >> the on-off periods between 300 and 800 usec. No difference. >> The >> receiver works with my TV remote control. > > --- > If it works with the remote control, then I suspect that what's > wrong > is that your transmitter carrier frequency is off-frequency > just > enough to give you glitch outputs from the receiver. > > why not try monitoring the output of your receiver while > adjusting the > CW transmitter carrier frequency until you get a solid output > from the > receiver? > > Diddle the TX freq control back and forth to find the edges of > the > receiver's passband and then set the control midpoint between > them. > > Also, make sure that the output of your receiver is properly > pulled up > to Vcc if it doesn't have a totem-pole output, and make sure > it's DC > coupled into whatever it's supposed to be driving. > My receiver circuit already complies with the suggestions in your last para. I tried the freq adjustment but it's no good. My Tek 2236 scope with a built-in frequency meter is temporarily out of commission and I haven't yet found time to dig out my old Hameg counter - the gated type. The scale on the basic 15MHz single-trace scope I'm using now seems to be quite accurate (as visual reading of scope traces go) when I checked it against mains waveform. According to that scope, the adjustment range is about 32-42kHz. Most IR receivers seem to be quite tolerant of reasonable amounts of frequency mismatches. Datasheets for 38kHz types indicate about 50% efficiency at 36 and 40kHz, and I've been testing my circuit at Tx-Rx ranges from a few inches to 3 ft.
From: Jim Thompson on 8 Apr 2010 15:41
On Fri, 9 Apr 2010 00:55:18 +0530, "pimpom" <pimpom(a)invalid.invalid> wrote: >John Fields wrote: >> On Thu, 8 Apr 2010 14:14:07 +0530, "pimpom" >> <pimpom(a)invalid.invalid> >> wrote: >> >> >>> I'm not using a readymade transmitter. I made my own using a >>> 38kHz carrier, switched on and off in bursts. I started out >>> with >>> about 500usec on, 450usec off. When that didn't work (the >>> received waveform appears briefly and then disappears), I >>> varied >>> the on-off periods between 300 and 800 usec. No difference. >>> The >>> receiver works with my TV remote control. >> >> --- >> If it works with the remote control, then I suspect that what's >> wrong >> is that your transmitter carrier frequency is off-frequency >> just >> enough to give you glitch outputs from the receiver. >> >> why not try monitoring the output of your receiver while >> adjusting the >> CW transmitter carrier frequency until you get a solid output >> from the >> receiver? >> >> Diddle the TX freq control back and forth to find the edges of >> the >> receiver's passband and then set the control midpoint between >> them. >> >> Also, make sure that the output of your receiver is properly >> pulled up >> to Vcc if it doesn't have a totem-pole output, and make sure >> it's DC >> coupled into whatever it's supposed to be driving. >> >My receiver circuit already complies with the suggestions in your >last para. > >I tried the freq adjustment but it's no good. My Tek 2236 scope >with a built-in frequency meter is temporarily out of commission >and I haven't yet found time to dig out my old Hameg counter - >the gated type. The scale on the basic 15MHz single-trace scope >I'm using now seems to be quite accurate (as visual reading of >scope traces go) when I checked it against mains waveform. >According to that scope, the adjustment range is about 32-42kHz. > >Most IR receivers seem to be quite tolerant of reasonable amounts >of frequency mismatches. Datasheets for 38kHz types indicate >about 50% efficiency at 36 and 40kHz, and I've been testing my >circuit at Tx-Rx ranges from a few inches to 3 ft. > It'd be nice to see your circuitry. I'm contemplating my navel as to how to roll my own IR repeater... so I can control the cable converter (located in another room) from my office :-) ...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 | The only thing bipartisan in this country is hypocrisy |