Ultra Violet light sensor circuit

Discussion in 'The Projects Forum' started by BobW55, Dec 28, 2014.

  1. BobW55

    Thread Starter Active Member

    Jul 22, 2008
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    0
    I am trying to DIY my own UV sensor to use with a Davis Weather station.
    Davis wants an outrageous price of over $300 for theirs which probably only has $20 worth of parts in it.
    The specs I need are:
    Detectable wave length 280 - 360 nm (UVA & UVB)
    Analog output close to 150mv per uv index 1-15

    The weather station has a 3.0 volt supply and turns on the sensor about every minute.
    I know in the actual Davis sensor the is a photo diode and an amplifier, possibly a trimmer or multi turn pot to calibrate it with.
    MY Questions:
    1) Can someone recommend a ready made board that would come close to these specs?
    2) Can someone recommend a photo diode that would have the required UV specs?
    3) If I have to use a photo diode, what is a good amplifier chip to use?

    I can handle the circuit building and such, just suck at component selection.

    Thanks
    Bob
     
  2. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
    5,676
    899
    How are you going to select that band to detect? Most common filters cut-off at short wavelengths (e.g., 280 nm), but transmit throughout the visible. A monochrometer will work, but short of that, you may find some specialized filters that will work, such as: http://www.asahi-spectra.com/opticalfilters/uv_broad_bandpass_filter.html

    I suspect you will need either two detectors or a chopped optical system so you can compare total or visible to UV only.

    As for the photodiode, have you even searched? Even DigiKey lists several options.

    BTW, a 10:1 or 15:1 ratio of parts cost to price is probably not tha unusual. Have you considered the cost of your time plus shipping (for parts, not your time) for a DIY project?

    John
     
  3. BobW55

    Thread Starter Active Member

    Jul 22, 2008
    43
    0
    Actually there are several manufactures of photo diodes specifically made to detect only the UV wave lengths I am interested in. There are also several diode/amplifier boards ready to be had that also detect the desired UV. Some use an analog output while others use a 12c output.
    Since I can not control how the Davis station computes the UV index, I can only try to match the input voltages required.
    I was hoping that maybe someone else has already gone down this path and could better direct my search. Even when I have found the desired electronics, I still have to build a housing and mount.
    As for my time, that is why many call electronics a hobby. I have already built several projects to control my humidifier based on outdoor temperature and inside humidity. (PIC/LCD Based) and antenna rotor controller, several power supplies, numerous LED projects.
    I like to tinker what can I say.
     
  4. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Sorry, I miss your point. Buy it or make it. $300 sounds like a bargain.

    John
     
  5. BobW55

    Thread Starter Active Member

    Jul 22, 2008
    43
    0
    Have a sensor board working, But trying to get the proper gain out of the amp is a real bugger.
    I either have too much, (can not get it to zero in total darkness) or have it so low that I loose response.
    But hey, only $20 into it and some of my time.
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,094
    3,033
    Go ahead and post your schematic. Someone can likely help you smooth things out. Look into "instrumentation amplifier" circuits using op-amps. They are designed to give control of zero and span.
     
  7. BobW55

    Thread Starter Active Member

    Jul 22, 2008
    43
    0
    wayneh,
    Thanks for the reply.
    I do not have a schematic to post, would love a schematic to this thing.
    I am using this sensor: http://www.thanksbuyer.com/a24b-uvm...ut-w-signal-amplification-linear-output-29218
    I have googled myself to death looking for even a spec sheet. I did finally translate the Chinese to find out that the bottom trim pot (as shown in the photo) adjust the zero. and the other adjust the output or gain. I have the gain adjusted about where it should be but still cannot get it to zero out in the dark.
    The zero adjust trimmer pot is 1K, I was going to try a 10K and if not a 100K and see if I can get it to zero out then.
    It has the correct frequency response to UV light that I need.
    Since this hooks up to a Davis weather station, I have no way to adjust the programming of the ADC inside the console.
    Still is way cheaper than the $300 Davis wants for their UV sensor.

    Bob
     
    Last edited: Mar 14, 2015
  8. BobW55

    Thread Starter Active Member

    Jul 22, 2008
    43
    0
    After reading up some more on OPAMPs that have a zero offset, I think I am facing the problem of too low voltage.
    I can not read the markings on the opamp to see what kind it is, but I know it is rated (According to the web site) for Min 5 volts, I am only using 3 volts.
    Hoping that it has a pin out similar to others I was thinking of replacing it with a 1-2 volt minimum variety.
    Checking on Mouser now.
     
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