Dropper for blind people

Hi everyone, as the title suggests, I'd like to make a dropper for a blind girl with a 3D printer and Arduino.
My first idea was to use a laser and a photoresistor sensor in a small dark place printed in 3D (so the ambient light don't affects too much the photoresistor), but I've read that this kind of sensors are unreliable for this purpose. On the same principle, another way to make it is to use an IR sensor (that is faster on detection I believe), but I don't know if this is a good idea. This approach also have a problem for blind people, the drops should falling exactly inline with sensor.
Any suggestions?

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If you pulse your emitter (whatever it is) at ..say 5000 Khz 5Khz then filter all the low noise (i.e. High pass filter) you can reject the ambient light and 60 to 240Hz flicker.

Thanks you very much for the answer.
I think that I've roughly understand what you mean (I'm sorry, but I'm a beginner).
Remains anyway the problem of falling drop exactly inline with the emitter and the sensor for a blind person.

You should be able to find articles on modulating light beams for detection.

How wide are the drops?

Google Rhom RPR-220 sensor. I know there are a number of similar sensors that work on reflection and have the emitter and receiver in one package.

Thank you very much, I'll search online that articles (LDR has to do to it?)

Anyway, to answer to your question... Like water drops, essential oil and things like this. Obviously I don't make it for medical porpuse..

That is a pretty fast PWM :grin:

..... thanks for the catch, should be 5k or 5000 HZ

Thanks so much for your help! It seemed to me a bit too fast, but I've supposed that was a typo in fact. No problem!

Glad I could help.

The frequency is only so you can separate the 240 HZ from your modulated signal. The 240Hz came from reading several LED's run at that frequency as it is about the limit of the eye seeing the "flicker"

Don't use photoresistors, they are way too slow in reply time, use phototransistors (or also better, photodiodes, much faster) :wink:

I'm really sorry for the late reply. Anyway, thanks so much for your suggestion! With these sensors I should also use the modulated light beams technique (as JohnRob suggested), right?

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