I recently purchased the photodiode here and I am a bit confused on how to implement it. The reviews are all mixed on what is what, and the voltage for each is different so I am trying to be rather cautious so as to not burn one out. For some reason, it lists the photodiode as being the clear package and the tinted being the ir led, which seems strange to me. I have seen this post as well, and I am not sure of it as well. The diagram shows the cathode going directly to the 5v+, where I am used to putting a resistor before the diode. All I am trying to do is read whether it detects light or not with a microcontroller. How would I wire these? Oh, and the specifications listed on the website are different from those listed on the package. Any help is appreciated.
Electronic – How to use this type of photodiode
infraredledphotodiode
Related Solutions
The usual configuration is to use a transimpedance amplifier. This takes the current output of the photodiode and converts it to a low-impedance voltage signal.
simulate this circuit – Schematic created using CircuitLab
The gain of the amplifier is set by R1. The maximum gain achievable without ringing in the response will depend on the op-amp used. C1 is used to reduce high-frequency noise. OA1 is chosen based on noise and bandwidth. The parasitic capacitance at the inverting input of the op-amp has a strong effect on overall performance.
With an appropriately chosen op-amp this circuit can be used up to at least 40 or 50 MHz (probably someone will comment that it is usable at higher frequencies --- 40-50 MHz is just the highest where I've seen it used). For higher frequencies you may need a specially designed receiver, which is basically the same circuit but integrated to reduce parasitics.
The simplest way to connect a photodiode (even an LED can be used in this way as a photosensor) is as below:
simulate this circuit – Schematic created using CircuitLab
Note that the photodiode is reverse biased through the 1 Meg resistor R1. The photocurrent generated by the diode opposes the flow of leakage current through this reverse biased diode, said opposition increasing with more light on the diode junction. The voltage at the junction point thus rises in voltage with increase in light.
The schematic on the left will have fairly low voltage at the ADC pin. To increase this voltage, an op amp can be used as a non-inverting amplifier, as shown in the schematic on the right. In the example shown, this gain is Gain = 1 + (R3/R4) = 9.9182.
This voltage gain results in a greater reading at the ADC pin, potentially making use of a greater part of the ADC's input voltage range.
Other applications of op-amps for photodiodes include:
- as a transimpedance amplifier, to directly amplify the photocurrent, without use of a biasing resistor
- as a voltage follower (unity gain buffer) for the voltage divider formed between diode and biasing resistor
Note:
One must ensure, though, that the voltage after amplification does not exceed the 5 Volt supply. If the op-amp is powered from the same 5 Volt supply as the Arduino, this is automatically taken care of, as the op-amp's output gets clipped at its upper supply rail, or even lower if the op-amp is not a rail-to-rail type.
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Best Answer
It's most probable that the clear package is the emitter.
It's very probable that the longests lead in each case is the Anode in both cases - ie the NON-bar end of the LED.
Photodiode are usually used in the reverse biased mode. eg like the circuit below from here
The reverse current of the diode varies with light level and is converted to a varying voltage by the opamp.
The circuit below from here -> Gamma Photon Radiation detector is from Maxim Application Note 2236, and is used to detect Gamma Rays, aka Gamma Photons. This is done using a PIN duide whoch does not respond to visible light, but the principle is the same and as this is a low npise high performance circuit, the notes and the circuit itself give a good feel of what is needed to get best results.
A zilllion circuits from here and from here