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 91 Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: How does analogRead know minimum and maximum value on: January 11, 2009, 04:09:36 pm Thanks for all the answers.. I think I acutally got most of it. Well except for the binary part. But then again I didn't even try to understand that. My initial reason for asking was trying to figure out why some tutorials online used a resistor between ground and the sensor, and I certainly understand why and how that works now. Even more actually. Big thanks to everyone who chipped in with advise!
 92 Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: How does analogRead know minimum and maximum value on: January 11, 2009, 06:29:23 am Ok I got the voltage divider concept figured out. But that raises further questions. Actually theories, would this assumption be correct?Lets say I use a potentiometer I have +5V in the first pin and ground in the third and in the middle I have a voltage divider connected to my analog in pin. R1 = 0Ohm to 1KOhm, I´ll use 500Ohm for this calculation = 500OhmR2 = Full potentiometer resistance pin 1 and pin 3 = 1KOhmVin = +5VVout = (R1 / (R1+R2)) * Vin = (1000 / 1500) * 5 = 3,3333 But if I have a CdS resistor I have the first pin in +5 and the second one in ground/analog in. But I then I would be measuring after only one resistor. That would give +5V constantly. So therefore I must use a resistor with the highest resistance of the CdS resistor to connect the circuit to ground.R1 = CdS resistor 2-5 KOhm, I'll go with 4KOhm here R2 = 5 KOhm ordinary resistor Vin = +5VVout = (R1 / (R1+R2)) * Vin = (5000 / 9000) * 5 = 2,7 In a sence I could make the CdS resistor more or less sensitive by using a smaller or larger resistor as R2. Have I got it right?
 93 Forum 2005-2010 (read only) / Frequently-Asked Questions / Re: How does analogRead know minimum and maximum value on: January 11, 2009, 04:39:49 am So in a sense it doesn't know what max and min are? I think I should read up on voltage divider before I ask any more questions. Thanks for the quick reply.
 94 Forum 2005-2010 (read only) / Frequently-Asked Questions / How does analogRead know minimum and maximum value on: January 11, 2009, 03:26:49 am Maybe it's because I don't have enough experience with electronics but I have a hard time understanding how the analogRead values are set. I understand what it measures and how. But how on earth does it know what the minimum and maximum values are of different parts like a potentiometer, CdS resistor and so on? Ofcourse a zero resistance would be a good minimum value but it still doesen't explain how it knows when it hits max. Best regards Markus
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