?Understanding signals 38 kHz ir

Driver

I have checked the wiring and programming very carefully. Both are ok. Still the picture on the scope is not right. The detector never gives a stable wave in response to an object. In fact, the presence or absence of an object makes no difference at the output. I ran another program to sweep through a wide range of frequencies. First I placed an object where it would be detected. Got a good strong stable recognition signal at 45.55 kHz. The difficulty now is that the recognition signal is still not affected by the presence or absence of the object. First I pointed it up in midair. No help there. Next I placed the led on a lead and held it enclosed in my fist. Still a strong detection signal. Perhaps there is some other source of ir at that freq. With the led enclosed in my fist and the detector pinched between finger and thumb (all ir paths blocked?) still recognition. What is triggering the detector? After all was put away I thought of replacing the led with a resistor so the circuit could still function the same, but with no possibility of ir being generated. Thoughts?

allanlane5

The outputs of some IR-Detectors work better if you give them a 10KOhm pull-up resistor between the output and +5 volts. The IR-Detector will 'pull-down' its output to zero volts when it detects 38 Khz IR-modulated light. But some of them simply let the output 'float' up when no IR-signal is detected. Adding a 10Kohm pull-up will insure your BS2 can see a 'high' when the IR-Detector sees nothing.

Driver

Thank you for responding to my question.· It is the next night now and I am humbled.· As I rebuilt the circuit, I noticed that the led leads were bent in the wrong direction.· Surely I would not have wasted so many hours on an accidentally reverse biased led.· Alas, that is the case.· Correctly biased it works properly.· And yet I still have a question.· With the led reverse biased, there was no ir being generated.· But 45.55 kHz was a frequency that caused the detector to trigger.· When I correctly built the circuit tonight, I downloaded the 38 kHz program.· Last night I had changed it to 45.55 kHz and tonight that value was still being used.· If I use 45550, the detector works exactly the opposite of expected.· It gives a detection signal when nothing is present and takes away the detection signal when I place my hand in front.· When I use 38500, the detector works just as it should.· How was the detector triggering last night?· The reverse biased diode was not producing any ir.· The freq was present at P7 and also at the portions of the circuit connected to P7.· But how was it getting to the detector.· Stray capacitance?· Also, why does using 45550 rather than 38500 cause the detection to invert.· The wave form does not invert.· Just the wave form's reaction to the presence of an object.

allanlane5

The operation of electrical noise, coupled through air or through capacitance, is very hard to predict, and very hard to duplicate.

I assume that the 45550 hz would have some 'noise' components that would couple through to the IR-Detector. When a strong reflection is made, then the IR-Detector is 'forced' not to detect.

The point being, you want to operate devices in the manner in which they were designed to be operated, because that's the way of reliability and predictability.

Mightor

If you're working with a laptop, make sure you disable your IR port in the BIOS or disable the device in your Device Manager. Switching off the IR discovery service I noticed to be insufficient. I found that the signal from that bounced off my T-Shirt and onto my robot's sensors without any problems causing very odd behaviour. It's quite amazing how many times you can make it bounce off stuff before it no longer interferes.

Gr,
Mightor

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