### Author Topic: photoresistor resistor question  (Read 1428 times)

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#### Spiffyguy

• Jr. Member
• Posts: 20
##### photoresistor resistor question
« on: April 08, 2008, 10:18:23 AM »
I am fair new to electronics so I want to make sure I have this right before I start soldering stuff. I am trying to verify the correct resistor for my photocells.  I have a medium photoresistor from Radio Shack. I tak emy multimeter and set it to 20kohms. it reads 2.57.  so this is really 2570 ohms or 25700 ohms?  my dark reading I set the meter to 200k and it shows a reading of 67.5  so I am not sure what the exact reading is.  Still figuring everything out.  Near as I can figure I need a 5k resistor for the photocells.  Is this right?

Thanks

#### superchiku

• Supreme Robot
• Posts: 953
• cooll
##### Re: photoresistor resistor question
« Reply #1 on: April 08, 2008, 10:46:11 AM »
man when u set ur multimeter to 20k that tells u that the max reading which ur multimeter can read is 20k in short now ur multimeter is ranged between 0-20 k a reading of 2.57 would mean 2.57 k or 2570 ohms and ur reading in dark is 67.5 k ohms

now getting into the mathematical parts ur resisitor value should be ~(2.57*67.5)^0.5 K OHMS
JAYDEEP ...

IT AND ROBOTICS ENGINEER

"IN THE END IT DOESNT EVEN MATTER"

#### Spiffyguy

• Jr. Member
• Posts: 20
##### Re: photoresistor resistor question
« Reply #2 on: April 09, 2008, 08:12:37 AM »
What is the ^ symbol in your equation?

If I input 2750 as my minimum and 67500 as my max into the resistor spread sheet it shows me i need a 5k resistor.  Just want to make sure before I buy the wrong one.

#### superchiku

• Supreme Robot
• Posts: 953
• cooll
##### Re: photoresistor resistor question
« Reply #3 on: April 09, 2008, 08:34:54 AM »
well if u look in the tutorials ull know that ^ implies power when i say 2^2 it means 2 to the power 2 which is equal to 4
JAYDEEP ...

IT AND ROBOTICS ENGINEER

"IN THE END IT DOESNT EVEN MATTER"