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This fruit is simplistic as there is a thin skin surrounding it. Inside it is a tiny ball of liquid and that is where the dense seed forms. The is seed much more denser in comparison with the liquid and the skin, you could almost neglect their presence in regards to density. So my purpose is to manipulate the wavelength of a wave such that it penetrates the skin but reflects of the seed if it is formed. Like the Rutherford gold foil experiment. I am aware of techniques such as the "Fourier transform infrared spectroscopy" but I am not an expert on this.

Bezal-el
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  • To say that you want to make an IR sensor is not exactly right. You are trying to make a proximity sensor using IR. – JaySabir Aug 03 '20 at 08:48
  • As long as the object you want to see through is transparent, you only want to detect motion (not absolute distance) and you tilt the sensor enough that it isn't blinded by the specular reflection, almost any IR led should work. If it isn't transparent, this becomes an extremely hard problem. – user1850479 Aug 03 '20 at 13:47
  • My object isn't transparent and there lies the problem :) – Bezal-el Aug 04 '20 at 06:38
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    You already asked this at. [Is there a way to vary the frequency of an IR / Ultrasonic sensor?](https://electronics.stackexchange.com/questions/514508/is-there-a-way-to-vary-the-frequency-of-an-ir-ultrasonic-sensor) This rewrite needs to be an edit to fix the lack of clarity and specificity there. **DO NOT REPOST CLOSED QUESTIONS** rather edit to fix them. – Chris Stratton Aug 04 '20 at 12:38
  • I am sorry about that, I did not know. – Bezal-el Aug 04 '20 at 17:51

2 Answers2

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You cannot realistically change the "frequency" of the infrared emitted from an infrared LED.

The wavelength is more or less a fixed range determined by the semiconductor material of the LED.

The current through the LED will probably have some (slight) influence on the the center of the range, but not enough to do anything useful. You will not vary the frequency from 300GHz to 430THz.

Think of colored LEDs. The color is determined by the semiconductor material that forms the diode junction in the light emitting diode. You can't "tune" a blue LED into a red one.

In the same way, you can't change what range of infrared wavelengths an infrared LED emits. There are infrared LEDs available that have their peak sensitivity at different wavelengths, but the differences aren't as drastic as what you seem to want.

Infrared detector diodes have similar restrictions, though not as bad as the emitter.

Infrared detectors are also often sensitive to visible light as well as infrared. You still won't get the range of wavelengths you want out of an infrared detector diode, though.

Most of the things you could use for distance detection have similar restrictions.

Ultrasound is often used to detect the distance between two objects. The emitter and detectors are usually piezoelectric crystals, though, that operate over a fairly narrow frequency range. That's the same problem you have with infrared.

Radar is another method used to detect distances. Any typical implementation will also use a particular frequency or (relatively narrow) frequency range.

Maybe you should explain what you are trying to do. There might be a common way to do it that other folks use all the time.

Now that you've explained what you are really trying to do, it seems that what need to do is something like "egg candling."

You are trying to tell if seeds are growing inside a pod.

The simplest way I can think of to do that is to just look "through" the pod with a bright light. Either by eye, or use a camera to record progress as the seeds grow.

Just hold your pod to a (very) bright light, and look through the pod for shadows.

It looks like this for an egg:

enter image description here

Borrowed from the linked page on egg candling.

JRE
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  • I think a (very) bright light and a camera are your best bet. Like how you check to see if there's a chick in an egg. – JRE Aug 04 '20 at 06:46
  • Yes exactly like this , but where does the bright light and camera fit in ? Infrared vision is kinda out of the question as the seed shows no heat maps – Bezal-el Aug 04 '20 at 06:50
  • [Like "candling" a chicken egg.](https://keeping-chickens.me.uk/chickens/how-to-hatch-eggs/candling-eggs/) Bright light behind the pod, use the camera to record pictures of the shadows of the seeds. – JRE Aug 04 '20 at 07:27
  • Wow i never thought of that idea, the light should be really bright. Thanks – Bezal-el Aug 04 '20 at 07:32
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None of the components on the sensor module are relevant to frequency. Those modules have a Wheatstone bridge, transistor, and a variable resistor to change the sensitivity (distance from the object). You are entirely dependant upon the IR transducer's (that black LED) capability to detect specific part of the IR band. Secondly, the IR sensor has nothing to do with the density of an object. for Example, A glass absorbs most of IR light, and it is essentially opaque for IR.

JaySabir
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  • No Wheatstone bridge and no (single) transistor in that module. It (mis)-uses an LM358 as a comparator. – JRE Aug 03 '20 at 09:17
  • @JRE I wasn't talking about THAT exact module. are you saying it can't be built with a Wheatstone bridge? – JaySabir Aug 03 '20 at 09:25
  • I'm saying I've never seen it done, and I don't know why you'd do it. – JRE Aug 03 '20 at 09:27
  • There are many ways of doing one thing - doesn't mean others are wrong. – JaySabir Aug 03 '20 at 09:32
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    Point to a module that uses a Wheatstone bridge in an infrared presence detector. My argument is with the assertion that "those modules have a Wheatstone bridge, transistor." "Those modules" are common and almost all look alike - and none of them use a Wheatstone bridge. – JRE Aug 03 '20 at 09:40
  • Alright, you might not find a WSB based module. But, my answer was perfectly fine even with my assumption. – JaySabir Aug 03 '20 at 10:39
  • Thank you very much for the answer, so do you suggest an ultra sound for this problem ? – Bezal-el Aug 04 '20 at 06:39
  • @ImmanuelJzv ultrasonic will reflect through paper. Your best bet is exploring RF. – JaySabir Aug 04 '20 at 09:25
  • @ChrisStratton Come on man I was talking about common ultrasonic module HC-SR04. wouldn't it get reflected by paper? It is literally tuned to detect any hindrance. Sure go ahead build your own module that can give you raw data that can be analyzed. – JaySabir Aug 04 '20 at 19:58
  • An *air-coupled* sensor like an HC-SR04 is *beyond obviously* inapplicable. But that's not remotely representative of ultrasonic technology in general. You've made my point even more clearly: it's only possible to evaluate the *idea* of ultrasonic when you consider what a *suitable* ultrasonic setup would look like. All you've really done here is demonstrated that *you* are not qualified to design one - the feasibility of the idea when implemented by someone with a *good* understanding of ultrasonic technology (eg someone who has designed medical ultrasound) remains entirely unevaluated. – Chris Stratton Aug 04 '20 at 20:42
  • @ChrisStratton I realize that I didn't communicate my answer very well. Thanks and I will improve my answers now on. It is one of my first answers on this site. – JaySabir Aug 05 '20 at 04:01