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### Author Topic: \$50 robot photoresistor math  (Read 2521 times)

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#### pomprocker

• Supreme Robot
• Posts: 1,431
• Sorry miss, I was giving myself an oil-job.
##### \$50 robot photoresistor math
« on: March 15, 2008, 06:36:57 PM »
I am trying to do this photoresistor math.

In the darkest operating light I am have the dial set at 200k and i'm geting a reading of 80.00

and set at 200k in a spot of sunshine coming in through the window I am getting 00.23

This give me 4.2 after the equation?

So should I use a 4.3k resistor?

I originally tried it out with just using the 1.62k resistor that was listed in the parts on the tutorial, but not getting very good results.

• Supreme Robot
• Posts: 11,702
##### Re: \$50 robot photoresistor math
« Reply #1 on: March 16, 2008, 08:01:35 PM »
80.00 what? kohms? and .23 kohms?

Make sure your units are correct.

sqrt(80k*.23k) = 4289.5 ohms

sqrt(80*.23) = 4.3 ohms

#### pomprocker

• Supreme Robot
• Posts: 1,431
• Sorry miss, I was giving myself an oil-job.
##### Re: \$50 robot photoresistor math
« Reply #2 on: March 17, 2008, 12:03:00 AM »
80.00 what? kohms? and .23 kohms?

Thats what i'm trying to figure out. All I know is the multimeter was set in the 200k range and the display just said 80.00 or 00.23

• Supreme Robot
• Posts: 11,702
##### Re: \$50 robot photoresistor math
« Reply #3 on: March 17, 2008, 05:02:50 AM »
Go with the 4.3k, the other one is waaaay too low.

#### superchiku

• Supreme Robot
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• cooll
##### Re: \$50 robot photoresistor math
« Reply #4 on: March 17, 2008, 01:29:30 PM »
man if the multimeter was at 200 then it is reading 80k,
u shouldknow about the multimeter first its the basic and one of the most reliable devices
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