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I need advice on a project.

mikedavis

Everyone,

 

I have an idea for a project, and I need some assistance. 

 

I would like to use the RPi (or whatever is most appropriate) to create a light detector.

 

A long time ago, I built a circuit that had a cadmium selenide detector.  When light hit it, there was a change in its resistance, and I could use the difference between the voltage in and the voltage out to determine how much light the detector was seeing.

 

I have breadboard that I can use to get the circuit going.  I would like to be able to use the RPi to have a computer capture this information so I could run an experiment over a long period of time.

 

What materials would I need?

 

Mike Davis

  • 0

    Hi Mike,

     

    The selection of a MCU will depend upon the details of your long term project.

     

    Have you assessed if the sensor can cover the light lntensity levels you need?

    How ofter do you plan to sample the sensor?

    Are you just taking measurements or are you also doing some calculations to create metadata from the sampling?

    How are you planning to store the data?  Format, number of samples?  24 Hour operation?

     

    From the most basic level, you could use an Arduino to sample the data several times per second, do max min average calculations and write the data in Ascii to either your desktop or laptop computer.

    You could also use a SD card shield to record the data to download and process externally.

     

    So think through your project, resolve some of the questions and then you will have enough data to make some good decisions about your components.

     

    Hope this helps,

    DAB

  • 0

    The Arduino is a great tool, and it can be used very easily with sensors such as a light sensor that you mention. The real challenge is going to be whether or not you are able to get the output you really want with the Arduino.

     

    I think I may have interpreted your question slightly differently than DAB. From what you wrote, do you want the Rpi to be the cmputer reading the end data, and then writing that to a file? If so there are a number of somewhat complete posts online about using the Pi for serial communications with the Arduino. I think networking it with an arduino is probably your best bet, but do let us know a little more about the project before we suggest anyhting with certainty.

     

    Hope this helped

     

    John Moosemiller

  • 0 in reply to bltsandwich1

    So I posted a document in the Documents section that gives instructions for making the circuit.  I would like to use the appropriate materials to hook a computer up to that so I could make continuous measurements at regular intervals.  I hope that helps.

  • 0

    Mike, a couple of suggestions:

     

    Keep your circuit mostly as-is and use an I2C (or SPI) ADC chip to read the change in the LDR in place of a simple analogue meter. There are plenty of ADC's available with different resolutions and sampling speeds, perhaps something like this ADC081C027CIMK/NOPB - IC, 8BIT ADC, I2C, SAR, TSOT23-6ADC081C027CIMK/NOPB - IC, 8BIT ADC, I2C, SAR, TSOT23-6

     

    Another way might be to use a specific light sensor like TSL2550DTSL2550D   

     

    Either way, and as DAB suggests, you'll need to make sure the device you chose has the required sensitivity.

     

    Both of those suggestions could be interfaced directly to an RPi, or to an Arduino. Reading them at set intervals and writing the results to somewhere useful is simply a matter of writing some code to do it.