If I have an analog output value of 550 being printed with a photo resistor wired with a 10kohm resistor, how do I find the current? I didn't know where else to put this, sorry.

hscriber: If I have an analog output value of 550 being printed with a photo resistor wired with a 10kohm resistor, how do I find the current? I didn't know where else to put this, sorry.

I assume you mean you have a arduino analogRead() input value of 550 counts? I also assume you have an external 10k ohm resistor wired in series with your photoresistor with arduino +5vdc pin wired to one end of the 10k resistor and one end of the photoresistor wired to arduino ground and finally the junction of the 10k and photoresistor wired to an arduino analog input pin.

If all those assumptions are true then how to calculate the current flowing through the resistor/photoresistor voltage divider? First you need to convert that 550 count to a voltage. Do a (550/1023) X 5vdc = 2.688 volts.

Now calculate the voltage drop across the fixed 10k ohm resistor: 5vdc - 2.688 = 2.312 volts. Finally calculate the current flowing through the 10k resistor: 2.312vdc / 10,000 ohm = .00023 amps, or .23 milliamps.

Was this homework?

Lefty

Thanks a ton. And yes it was. It's just to make us realize the limitations on a project though.