Roaming toward the light...

MrFus

Im working on my boe-bot, Im learning the chapter 6 that is the one refering the use of the photoresistors... well after write and load the program to make the robot look for the source of light on the room i try it and works fine but the intensity of the source of light need to be to strong, I increase the value on the average factor to increase the sensibility but still is not working...·why this can be happening?·could be the·value on the resistors that i have on the circuit (220 ohms)?

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Mr Fus

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Panama City Beach, FL
http://microbots.tripod.com.mx
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Mike Green

The photoresistor sensor has a very very wide range of response with very high resistance indicating low light levels. The Stamp measures the time to charge or discharge a capacitor through the photoresistor. There's a good discussion of this on this webpage: www.emesystems.com/BS2rct.htm. The value of the capacitor can help set the effective range. If the capacitor is too large, the readings at the high light end may be too crowded together. If the capacitor is too small, the readings at the low light end might be too crowded together. What capacitor value are you using?

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I just looked at the Robotics text and realized I'm a little ahead of you. The above is discussed starting at Activity #4. When you're just using a resistor divider, you will need a higher resistor to get better sensitivity from the photoresistor. Look at the box on the top of page 199.

Post Edited (Mike Green) : 5/7/2007 4:39:20 AM GMT

MrFus

Thanks, yes I forget abouth the capacitor and the time of charge and discharge... Im current using the one that come on the text that is 0.01 microfarads... Im going to jump to the apendix F (the one refering the balancing of the photoresistors to be sure they·are working on the proper way) and I will make some modifications to the program of "roaming toward the light" to show the values of the photoresistors on the terminal of the editor and have a better idea of the values the sistem is using on the experiment.

Post Edited By Moderator (Chris Savage (Parallax)) : 7/11/2007 12:21:38 AM GMT

D Faust

If you are working in bright areas I suggest using the 104 small yellow capacitors that come with the kit. I think that they are .1 microfarads. They give you a reading that has more digits. I think that makes it more accurate.

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D Faust