Light Sensor issues - photodiode, phototransitor an LDR?

[cuteconnect]

Light Sensor issues

Please who can help me with an idea of the light sensor i can use as input for a system that takes solar insolation and feeds it into a microcontroller giving the output on an LCD the options i have are
a photodiode
a phototransitor
an LDR (light dependent resistor)

 

[sau_sol]

Re: Light Sensor issues

all the three will work i have interfaced all of them

the difference is the circuit diagram for each and the circuit complexity

the light intensity also matters to choose what to use



first clearify the question and the application

 

[wrak]

Re: Light Sensor issues

Thank u.
so nice of u.
that was my prob as well

 

[cuteconnect]

Re: Light Sensor issues

thanks for that piiece of reply. Please may i know the particular LDR you used since i cant get hold of photoresistors or phototransistors in the shops around here. i can only get LDR. can i also interface LDR with a PIC 18FXXX MCU. the picture below is the type of the LDR i have, can i make use of this one?

 

[nghtyvbz]

Re: Light Sensor issues

all the three will work i have interfaced all of them

the difference is the circuit diagram for each and the circuit complexity

the light intensity also matters to choose what to use



first clearify the question and the application

hi sau_sol,
thanks for the reply.. may you please advise what would be best to use, a photodiode or LDR for measuring sunlight? its a solar tracker project. the circuit should be less complex as well.
thanks

 

[ard]

Hi,

Broadly speaking, you need an LDR if you want quantitative readings about the light, and an Photodiode or Phototransistor for digital (present or absent) reading.

Also, the response time for an LDR is usually slower. In your app, I dont think this would be an issue, though.

So, like sou_sol said, depending on your schematic and the software you write, you could use any one of the three.

Regards,

Anand Dhuru

 

[nghtyvbz]

Hi,

Broadly speaking, you need an LDR if you want quantitative readings about the light, and an Photodiode or Phototransistor for digital (present or absent) reading.

Also, the response time for an LDR is usually slower. In your app, I dont think this would be an issue, though.

So, like sou_sol said, depending on your schematic and the software you write, you could use any one of the three.

Regards,

Anand Dhuru

Thanks Anand for the reply
See I am thinking of buiding a small prototype that would track the sun and would have a small PV panel too to charge atleast a 12V battery.

It would have a microcontroller, couple motors for 2 axis movement, a circuit, 4 or 5 sensors(Si PIN photodiode or LDR?) and a 12V battery.

I would write the code for microcontroller on MATLAB or something but I was just wondering should I use an LDR, I would need to provide current to it on the other hand should I use a photodiode I would'nt need to provide current to it. In fact the photodiode would provide current to the ciruit which could be fed into an Analog to Digital Convertor and eventually read by the microcontroller to do the needful.

Its just that its a energy saving project and use of an LDR sensor would do loss of energy but my aim is to save as mush as possible energy. Hence I was thinking of going with a photodiode instead of an LDR. Or am I wrong anywhere above? Also would a photodiode be more efficient to an LDR? to be honest I have researched a lot and have'nt seen one solar tracker to be working on photodiodes all work on LDRs. I was just curious whether using photodiode sensor would be good enough or not? may you please advise? thanks

 

[ard]

Actually, using the LDR would be far easier. Just wire up the LDR in series with a fixed resistor to form a potential divider and connect its other end to the ground, connect the other end of the fixed resistor to +5. The common point will now have a voltage that changes linearly with incident light. Feed this in directlt to an ADC pin on your micro, and there you are! Have 2 of these arrangements, and keep comparing the readings on both; track your panel till the readings match.

BTW, this arrangement will add less than a mA to your existing circuit, and would have no negative impact at all on its effeciency.

Using the photodiode instead, will not significantly lower the *total* current consumption, but will definitely make the software (and hardware, for that matter!) more complex.

Regards,

Anand Dhuru

 

[FvM]

Broadly speaking, you need an LDR if you want quantitative readings about the light, and an Photodiode or Phototransistor for digital (present or absent) reading.

All three are (more or less) linear sensors and can perform quantitative measurements. A phototransistor can't work at high light intensities and has a limited linearity due to the current gain variation. But a photodiode gives better linearity and less temperature dependance than a LDR. The spectral response is different however and the LDR's red/green centered characteristic may be an advantage in some applications.

The LDR as a variable resistance is a more versatile device, the current level of the sensor circuit e.g. can be scaled by a changing the operating voltage. The current of a photodiode can only be changed by varying the diode area or attenuating the light intensity.

P.S.:

Using the photodiode instead, will not significantly lower the *total* current consumption, but will definitely make the software (and hardware, for that matter!) more complex.

Not necessarily...

 

[Enlightenment]

If is looking at the sun, then a LDR is all you need. Those others are great, but have a very fast response time. Most solar projects don't need super fast light readings.

 

[fcaiii89]

You can use BPW34 photodiode as the sensor and then use the PIC16f877a as the microcontroller. You can then use the analog to digital converter (ADC) of MCU to measure the light intensity by means of the varying voltage. If you're interested, I can give you the circuit or even the program. I used MikroC Pro as my compiler.

You can display the result in an LCD or in the hyperterminal if you like.

Felipe