response of a voltage divider with a photoresistor...voltage divider circuit and output formula r p...
TRANSCRIPT
Response of a Voltage Dividerwith a Photoresistor
ME 120 Noteshttp://me120.mme.pdx.edu
Gerald Recktenwald
Portland State University
Department of Mechanical and Materials Engineering
October 4, 2017
ME 120: DC Circuit Computations with Excel
The Goal
• Show how a photoresistor output can be converted to voltage
• Analyze a voltage divider
• Set up an Excel plot of voltage divider output as a function of resistance
ME 120: DC Circuit Computations with Excel page 1
Photoresistors or Photocells allow circuits to respond to light levels
photons
In an electrical circuitthe resistance dependson light intensity
ME 120: DC Circuit Computations with Excel page 2
Photoresistor in the Tinker Kit
ME 120: DC Circuit Computations with Excel page 3
Voltage Divider Circuit and Output Formula
Rp
Rc
Vs
Vout
I
Apply Ohm’s law for the entire circuit
Vs = IReq =⇒ I =Vs
Req(1)
and again for the voltage drop across the constant resistor
Vout = IRc (2)
Substitute the I from Equation (1) into Equation (2) to get
Vout = VsRc
Req
Or, since Req = Rp + Rc
Vout = VsRc
Rc + Rp
ME 120: DC Circuit Computations with Excel page 4
Information from the Sparkfun Web site
1. Go to the Sparfun web site, https://www.sparkfun.com/
2. Enter “photocell“ in the search box to
get the “mini photocell” product page:
https://www.sparkfun.com/products/9088
The photo to the right is from the
Sparkfun product page.
3. Click on the “Documents” tab
4. Get the datasheet from the link:
https://cdn.sparkfun.com/datasheets/Sensors/LightImaging/SEN-09088.pdf
ME 120: DC Circuit Computations with Excel page 5