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Author Topic: Photodiode for light barrier  (Read 1662 times)
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Hello,

I want to meassure the speed of a little model car, so i wrote a Programm (Picture is attached) which reads the output from my arduino and plots the values.

First i wanted to use LDR´s but they are to slow. Now I want to use photodiodes, but i dont know how to use. In the Arduino Playground i spotted that you can use them like LDR´s but before i order them i rather ask if its right. And are this Photodiodes good for me: http://tinyurl.com/d7p48y5

Can I built this (and will it work smiley-grin). Picture is attached.

Thanks

DJburner

P.S.: Sry for my very bad english, im from germany smiley-wink


* Laser.png (15.62 KB, 1628x729 - viewed 69 times.)

* 0.4.PNG (95.59 KB, 1360x703 - viewed 64 times.)
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Classicly, you need a "transimepance amplifier"  connected to the PD.
see
http://www.jensign.com/PhotodiodeAmpDesign/

A 1 meg R feedback with a 100 pf cap across it might work, to prevent oscillation.

This approach minimizes internal capacitance of the PD and increases BW.

jb
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Photodiodes are typically used where very high speed is required. In your application, a phototransistor would be more suitable, because it is much more sensitive than a photodiode, but still much faster than a LDR.
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"a phototransistor would be more suitable, because it is much more sensitive than a photodiode,"
Sorry, a photodiode better way to go. The phototransistor is essentially a slow photodiode with much more capacitance.
But heck, either will work for a simple light interrupter where response time not an issue. But a PD with an op-amp
in transimpedance circuit is the standard way to go.
And he doesn't need a laser, any old led will work.
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"a phototransistor would be more suitable, because it is much more sensitive than a photodiode,"
Sorry, a photodiode better way to go.

Only if you need high speed, which the OP doesn't.
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Leaving aside the debate between a photodiode and a phototransistor for now, which method do you intend to use to find out the speed and distance?
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