
#1
Nov812, 09:57 PM

P: 29

If I have a circuit similar to this: http://i.imgur.com/JaUGb.png
I am reading in voltage as an input from Vin, when switch is closed, and am wanting to find out the unknown resistance R. Similar to dmm...what would be the best approach? Reading the voltage, calculate current to find R? 



#3
Nov912, 01:23 AM

Sci Advisor
P: 4,003

The voltage at Vin will be proportional to the resistance R.
So you can say V_{in} = R / (R + 1000) * 5 volts Once you measure the value of V_{in}, you just put it in the above formula and work out the value of R. For example, if the value of V_{in} was 3 volts, you would move the 5 volts and the (R + 1000) to the left of the equation and say 3 volts / 5 volts = 0.6 So, 0.6 * ( R +1000) = R so 600 ohms = R  0.6R = 0.4 R R = 1500 ohms Now check, 1500 / 2500 * 5 volts = 3 volts So, the answer is right. 



#4
Nov912, 08:07 AM

P: 29

Finding unknown resistance
thanks vk, going to give it a try with my module.



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