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Measuring Current recieved from a Photodiode

Hi all, I cant figure out how to calculate the current from a photodiode! I am using a photodiode in reverse bias to detect and infrared signal incident on it from a transmitter. Have built the recieving circuit by incorporating a gyrator circuit- as a constant current source to the LED. when a signal of the frequency of interest in incident on the photodiode, the time constant of the photodiode is such that it cannot react fast enough, hence producing a low signal at the end of the photodiode. This low signal is then rectified and amplified by a transimpedance amplifier.

(For circuit diagra, - refer:

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Have the circuit going. I was wanting to test the accuracy of my circuit, hence:

How do i calculate the amount of current that is top be produced by the photodiode? (for experimental pursposes keeping the height of the transmitter constant at 5 cm and moving the transmitter away from the reciever to 1 cm, 2 cm. 3 cm and so on)

the photodiode i am using is a BP104

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the transmitter generic 5mm
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I am driving the LED for short bursts at 1A.

any ideas?

Reply to
generous.boy
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Zero info on the color of the driven LED, zero info on the luminous efficency of that LED, etc makes it impossible to calculate; all one can say is that a change in the output of the detector *might* be seen (oops! might not - had them pointing the wrong way).

Reply to
Robert Baer

I've looked at your webpage. Seems that you don't modulate the ir link with an carrier. I suggest you have a look how an ir remote control for TV works. Another good source is to read the irda spec.

In short:

- use a carrier frequency to filter out ambient light

- use a LED/photodiode pair of the same spectral peak

- use a photodiode with an ir filter (black outfit)

The gyrator is not checked. For a simple try exchange it with a 100K resistor.

It's best to use an integrated tv remote receiver IC. They do all in one package for cheap!

You can aks me if you have further questions.

regards - Henry

Reply to
Henry Kiefer

- using a carrier freqncy, would mean i have to emit short bursts. I have looked into it and even experimented with some matched modules (TSOP IR). My system is time critical to the point of micro-seconds. Hence i tried using Pulse Position Modulation. It does have the pitfall of multipath interference. But i'll live with it for now. (just want to get the system goin - so tht i can experiment my concept)

the one's i am using currently are both approx 950nm

am covering my reciever with black perspex (thinkin that will help)

when u say exchange with a 100k do u mean replace the 47ohm resistor with a 100k. I am sorry i dont think i understand when u say the gyrator is unchecked (novice :S )

i am using the gyrator as a constant current source, the only time it turns off is when i get a signal of interest. GB

Reply to
generous.boy

I'll plead ignorance here since I haven't built such circuits, but this looks useful:

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The author claims high speed requires a large bias. Page 33 and 36 look interesting. It seems to me that with the gain of these circuits being open loop, you need some assurance that the gain stage behaves well when clipped. Some amplifiers "stick" when clipped, which can reduce settling time, which is important to get the next pulse. [A more robust design would feed a high frequency sine burst with a compatible filter on the receiver. ]

I think a better approach would be to do the filtering and amplification in separate circuits.

Reply to
miso

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