What could be causing unstable output on TCS230, a CMOS color sensor?

[thavamaran]

TCS230 output problem. HELP URGENT!

Hi guys, I am working on TCS230, a CMOS color sensor, so I am really confused what the problem will be. please someone.


actually my sensor was working well, but the output, when i measured it in oscilloscope, its not stable, like an example.

i triggered to blue filter and measured a blue printed A4 paper, so during my measurement in oscilloscope, it varies greatly, it alternates crazily, like 3,98khz to 4.59khz and then back to 3.8khz, and go back to 4.83 khz, and return back to 3.39 khz, it just keeps alternating. so what i did was, i concluded that external light source is giving too much of trouble and i get a black box, stick it on my PCB all around the white LED and also the sensor, its covering around, the sensor is covered by 1.7cm plastic around it. So when now i measure it, the waveform actually got worst, it varies like hell and there is noise in the waveform now. its getting crazy. i really got no idea what to do.

my circuitry is like very simple, a color sensor and two white bright led by the side of it, i just design it by myself, do anyone can give me idea what would be the problem, please someone, and is there certain specification how the LED must be fixed by the side of sensor? please someone help me. cause once the sensor is stable only, i could do my pixel level analysis and sensitivity analysis.

 

[vk6kro]

I think you need to isolate the problem a bit.

For example if you can use a light meter watch the brightness of the leds and see if they are varying.

You can use a photodiode connected to a CRO to see if it can detect light variations on your coloured sample. You would know how to do this.

Look at the power supply to the LEDs to see if it has AC on the DC. Even a little bit may be too much.

Use another light source like a halogen light to light your sample and see if that improves the result. Is it because the halogen lamp was brighter? Maybe that is all it needs?

 

[MATLABdude]

thavamaran, remember that the TCS230 output frequency is not proportional to wavelength, but to irradiance. If you're controlling brightness of the white LEDs using PWM, I hope you're not getting aliasing effects! (I don't know how fast the TCS230 responds to changing inputs):
http://www.taosinc.com/productdetail.aspx?product=3

Also, did you put in the decoupling capacitors on the power lines, as recommended by the datasheet? Or solder the chips a long time after cracking open the bag? As per the last page of the datasheet, they apparently don't like moisture so much (though this is just when you go to solder them in place)