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Topic: Read voltage drop from photoresister without a second resistor? (Read 1 time)previous topic - next topic

awawda

I am  starting to play with my Arduino Uno and have a question about hooking a photoresistor to my Uno. Most tutorials connect the photoresistor like this using a second resistor:

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`+5V --> PhotoResistor --> . --> 10K --> Ground                          |                        Pin X `

I think this technique is called a "voltage divider" and I understand how it can be used to read the variable voltage drop that occurs from the PhotoResistor.

My question is why can't I just measure the drop without the 10K resistor? In other words, would the following work (where we read the voltage drop from Pin X)?

Code: [Select]
`+5V --> PhotoResistor --> . --> Ground                          |                        Pin X`

Thanks a lot!

JimboZA

Because if the photoresistor goes to 0 ohms, you'll have a dead short across your 5v to 0v....
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awawda

Thanks! That makes sense.

Erni

Also pin x is connected to ground, so your reading will allways be zero

arbutus

Remember the path to the answer is always the path of least resistance!
Don't breath in the magic smoke!

Magician

What, don't have a resistor? Use a cap in voltage divider, here is tutorial:

JimboZA

#6
Jan 18, 2013, 03:42 amLast Edit: Jan 18, 2013, 03:45 am by JimboZA Reason: 1

Also pin x is connected to ground, so your reading will allways be zero

Oh, yeah..... that too. I forgot about that bit.
Johannesburg hams call me: ZS6JMB on Highveld rep 145.7875 (-600 & 88.5 tone)