Wanted Colour Temperature Meter Circuit from Lux Meter Circuit

Discussion in 'General Electronics Chat' started by Avid Solderer, Jun 17, 2013.

  1. Avid Solderer

    Thread Starter New Member

    May 30, 2013
    Wanted – Colour Temperature Meter Circuit from Lux Meter Circuit

    This avid solderer, constructor of devices to circuit designs of others, with very limited electronics understanding himself, would be extremely grateful for your help.

    I want to build a colour temperature meter to monitor a variety of experimental tungsten halogen light sources. This would use two silicon photodiodes, one behind a red filter and the other behind a blue filter. Since the spectrum of these lamps is continuous, no provision for a third photodiode behind a green filter, as incorporated in expensive commercial meters used to read fluorescent lights, is necessary.

    The attached pdf (http://www.***********/doc/20323528/Photographic-Color-Temperature-Meter) of a forty two year old Everyday Electronics article, featuring light dependent resistors, is what first sparked my interest in such an instrument, the simplicity of nulling a bridge circuit being particularly attractive. Advances in optoelectronics since then mean that newer devices, like spectrum corrected silicon photodiodes, are likely to achieve much better results.

    Hamamatsu publish a design for a luxmeter, item 4 on the attached pdf, (http://www.hamamatsu.com/resources/pdf/ssd/si_pd_circuit_e.pdf) and this seems like a good starting point, particularly since it works over an extended range of light intensities. But since their devices are not commonly available here in the UK, the photodiode of choice is the Vishay BPW21R, the data sheet of which is attached as a pdf (http://www.vishay.com/docs/81519/bpw21r.pdf)

    Can anyone suggest a radical recasting of the Hamamatsu circuit to achieve the same kind of bridge circuit as given in the earlier design, using a centre zero meter, several large ones of which I have, and the Vishay devices? I would be very glad of any suggestions.
  2. Georacer


    Nov 25, 2009
    Your first link is broken, since you copied a cropped version, as it is displayed in a text editor (notice the stars in the link). However, since you have uploaded the file anyway, the file is accessible.
    Avid Solderer likes this.
  3. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
    Avid Solderer likes this.
  4. Avid Solderer

    Thread Starter New Member

    May 30, 2013
    Georacer :- Sorry, can't think how that happened! But, as you say, the article is attached.

    mcgyver :- Many thanks for introducing this old guy to the amazing world of publiclaboratory.org. Those spectrometers are exactly what I needed as a kid! But they supply a little too much info. for my current needs, which is just a simple colour temperature meter reading in degrees Kelvin.