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Topic: Photodiode for light barrier (Read 1 time) previous topic - next topic

DJburner

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 :D). Picture is attached.

Thanks

DJburner

P.S.: Sry for my very bad english, im from germany ;)

lockinamp

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

dc42

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.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

lockinamp

"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.

dc42


"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.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

arduinoadrian

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?
Perseverance is 90% of the solution. The remaining 10% is more perseverance.

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