Society of Robots - Robot Forum
Electronics => Electronics => Topic started by: random robots on July 16, 2010, 08:19:59 PM
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i really hope one of you guys have used this- an rpm7136-v4r ir reciever. they aren't working right. they seem to have a continuos high output, even when there is no ir light pointing at it. could the problem be that i am not using coded data? it's what the datasheet recomends. also, could you tell me a good ir reciever that i can use for object detection?
thanks,
Patrick
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Yeah, those ir receivers only see ir from that particular frequency.
For object detection, use photodiodes.
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the led occilates at that frequency, so its not the problem. other suggestions?
edit: by coded i mean encoded signals from a remote, not the center frequency
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Hi,
It's good manners to include a link to a datasheet - we're here to help, but not to do your foot work.
[...] they aren't working right. they seem to have a continuos high output, even when there is no ir light pointing at it.
I bet it works just fine. A continuous high means that it doesn't receive a thing and when it does, it pulls towards ground (inverted logic).
could the problem be that i am not using coded data? it's what the datasheet recomends. also, could you tell me a good ir reciever that i can use for object detection?
Hard to tell what the problem is when you don't specify your entire setup.
What wavelength IR LED(s) do you use?
What distance?
Direct or reflective use?
Exact schematic?
The datasheet I found is not clear on whether it uses AGC "error handling" against Continuous Wave (CW) signals, but integrated IR receivers falls in two main categories: Those with a constant gain and those that uses one or another AGC algorithm.
Since they're often used for TV's and the like, a CW block makes perfect sense and will help eliminate errors, but when used for eg. security curtains, which by nature is CW, such block should not be used.
However, even with a block, you should still see some signal,starting with full modulation and then dwindling down (or rather up - requires a 'scope to see the fade).
If you want a receiver that works with CW (and for your app. you do), here's the only 3 from Vishay that will work: TSOP4038, TSOP5038 and TSOP58038. They're all 38 kHz devices, as their name implies.
Still, you should see something, no matter the AGC response used, so get the one you have working before anything else.
Just use a TV remote to verify that it works (Not a high speed one like B&O though).
But how exactly is your setup that doesn't work?
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to answer the questions above,
the led is 940NM wavelength,
distance is <20cm and the receivers have a range accurate of 20cm,
the application is reflective for object avoiding/following,
i can't show a picture of the schematic, but this may clear it up a bit,
+6 0
Ir receiver-\/-----------\ 36kHz 555 circuit-ir led
/ \
out-Voltmeter-/
The voltmeter is always at 6v, even if the led is directly pointing at it. the Ir receiver has a center frequency of 36kHz, so it probably won't work with a TV remote.
there may be some Ir interference, and i think that from my test, the receiver has an AGC algorithm. that or my reciever is defcetive.
Patrick
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Those IR receivers are tuned to a fairly narrow modulation frequency (check DS for spec). If the IR LED pulse frequency is not almost exact then the receiver will not detect the LED. Since you are using a 555 to create the LED pulses have you measured the frequency?
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*deleted*
accidental double post
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i haven't measured the frequency yet. is it possible to measure frequency with a multimeter? or do i have to use an oscilloscope?
Patrick
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Hi,
Those IR receivers are tuned to a fairly narrow modulation frequency (check DS for spec). If the IR LED pulse frequency is not almost exact then the receiver will not detect the LED. Since you are using a 555 to create the LED pulses have you measured the frequency?
I beg to differ.
Here's a curve from a datasheet (TSOP17xx, but they're pretty alike all of them):
(http://That.Homepage.dk/Img/Fresponse.png)
With a typ. range of 15m (direct) at 36kHz, it will have a range of at least 3m at 28.8kHz to 43.2kHz.
Outside that, there will be an output at a smaller range of course.
I'd rather blame the 6V supply, which they're not built for.
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ok, i used a resistor in between the 6v supply and ir reciever during the test. the reciever can handle up to 6.3v, so thats not a problem. it may be the current, though, and ill test that tonight. ill post results tonight.
Patrick
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Hi,
to answer the questions above,
the led is 940NM wavelength,
Fine then.
distance is <20cm and the receivers have a range accurate of 20cm,
For testing, you should use it direct until you have verification that it works that way.
I don't understand your mention of a 20cm range - it is 15m typical?
the application is reflective for object avoiding/following,
i can't show a picture of the schematic, but this may clear it up a bit,
+6 0
Ir receiver-\/-----------\ 36kHz 555 circuit-ir led
/ \
out-Voltmeter-/
Not really ;)
Use the code tag when you want to make ASCII schematics.
You shouldn't feed it 6V!
It's 5V but tolerate up to 5.5V (Don't be fooled by the "Absolute maximum ratings", they should be termed "If you transgress this, you will be in trouble",
And remember... Powered electronics seldomly stay at 25°C,
The voltmeter is always at 6v, even if the led is directly pointing at it. the Ir receiver has a center frequency of 36kHz, so it probably won't work with a TV remote.
You didn't try it and yet you tell me it probably wouldn't work??
Have some faith, it will only shorten your life a minute to test and probably give you back a couple of hours (at least) of trying to determine where the problem is by other methods available to you.
If it doesn't give any output with a TV remote, it's headed for the non-recycle bin.
And don't try to measure it with a voltmeter - we're talking ms timing.
Try this - and do it verbatim:
(http://That.Homepage.dk/Img/IRtest.png)
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ok, i used a resistor in between the 6v supply and ir reciever during the test. the reciever can handle up to 6.3v, so thats not a problem.
Yes, that IS a problem - 5.5V max. read what I just posted.
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ok so the problem is im feeding to much volts to it. I will also try the tv remote and see what happens. Alright, lower votage and test tv remote. ill post results soon.
Patrick
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guess what guys! i can haz results!
w00t!
ok down to the results
normal without ir interference-4.7v
tv remote on-3.5v
so the the remote had a pretty noticable affect on the reciever. im working on my 555 circuit, but this shows it still works. ill show more results from my 555 circuit soon.
Patrick
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Hi,
The circuit I gave you will be easier to use for the initial setup (a 'scope would be better of course) - if it gives of the least bit of light, the receiver is picking up IR.
To get the 555 spot on, you can use a trimmer to set the frequency and to get the best result, when you get a good signal, bounce it off a wall or increase the distance - the weaker the IR, the more precise the frequency has to be, so by bouncing the signal and increasing the distance (or even use a photographic Neutral Density Filter, usually just called an NDF filter, they come in various "darknesses" [never mind the illogical double F, it's like when saying an LCD display]), you can get the frequency spot on without measuring the frequency.
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would this lin be any use to you:
http://www.robotroom.com/Infrared555.html (http://www.robotroom.com/Infrared555.html)
ps. I do think that you are using the wrong detector, especially if this is your first time building an IR device
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ok si have the ir circuit ready and testable. ill test tonight. if it dosent work, im gonna buy some vishay ir recievers as Soeren mentioned above on my next robotics shopping spree.
Patrick
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they didn't work. the case is closed.