# I. Voltage Division and Loading > [!table] Initial Potentiometer Settings & $V_{out}$ > | Expected Voltage (V) | Measured Voltage (V) | Percent Error | | -------------------- | -------------------- | ------------- | | 5.000 | 5.0001 | 0.002% | --- > [!table] Adjusted Potentiometer Resistances & $V_{out}$ > | Expected Resistance ($k\ohm$) | Measured Resistance ($k\Omega$) | Percent Error | | ---------------------------- | ------------------------------ | ------------- | | 10.000 | 9.5457 | 4.543% | --- > [!table] Load Resistance vs Output Voltage > | Desired V_out (V) | R1 Initial Setting (k$\ohm$) | R2 Initial Setting (k $\ohm$) | **Measured V_out (**V) | **Best Adjusted V_out (**V) | R1 Adjusted Resistance (k$\ohm$) | R2 Adjusted Resistance (k$\ohm$) | | --------------------------- | ---------------------------- | ----------------------------- | -------------------------------- | ------------------------------------- | -------------------------------- | -------------------------------- | | 3.3 | 3.3952 | 6.6048 | 1.827 | 3.307 | 6.341 | 3.659 | | 1.5 | 7.034 | 2.966 | 3.698 | 1.497 | 2.838 | 7.162 | | 2.5 | 5.005 | 4.995 | 2.641 | 2.5081 | 4.846 | 5.154 | --- >[!table] Measured vs Expected Source Current >| Calculated Load Resistance ($k\ohm$) | Measured Load Resistance ($k\ohm$) | Percent Error | Measured V_out (V) | Measured I_R (mA) | Expected I_R (mA) | Percent Error | | ------------------------------------ | ---------------------------------- | ------------- | ---------------------------- | ---------------------------------- | --------------------------- | ------------- | | 100k | 99,852 | 0.148% | 2.44 | 0.505 | 0.51 | 0.980% | | 4.7k | 4,702.2 | 0.047% | 1.623 | 0.667 | 0.68 | 1.912% | | 10 | 9.954 | 0.46% | 0.00968 | 1.012 | 1.030 | 1.748% | | 0 | 0.072 | undefined | 0.008 | 1.016 | 1.032 | 1.550% | --- - Possible potentiometer benefits - Allows output voltage to be quickly adjusted - Makes it easy to observe loading effects w/o going thru process of changing resistors - Works w/o software - Smooth adjustments possible - Possible potentiometer disadvantages - Small adjustments make noticeable voltage changes - Wiper degradation over time - Large size - Use cases - Calibration & trimming - User controls - Prototyping - Simple systems where digital control isn't necessary # II. Voltage Division w/ LDR > [!table] Measured LDR Resistance at Different Light Levels > | Light level (Normal, high, low) | Measured Resistance ($k\ohm$) | | --- | --- | | Low | 6.8 | | Normal | 1.33 | | Bright | 0.36 | --- $\text{Voltage divider equation: }V_{out}=V_{in} \frac{R_{2}}{R_{1}+R_{2}}\to \text{using }R_{1}=1.33k\Omega,\text{ ideal resistance }R_{2}=680\Omega \approx670\Omega$ --- <div style="page-break-after: always;"></div> >[!figures] LDR Voltage Divider Schematic >![[circuit (2).png|center|350]] --- > [!table] LDR Output Voltages vs. Light Level > Determined location of LDR: $R_{2}$ > > | Light Level | V_out (V)| > | ----------- | ------------------- | > | Low | 4.72 | > | Medium | 3.19 | > | High | 0.721 | --- - Voltage divider worked as expected -> when LDR switched w/ $R_{1}$, circuit response is inverted b/c $V_{out}$ depends on which resistor is connected to the supply & which is connected to the ground. - Changing position from top <-> bottom changes whether increasing environmental light causes $R_{L}$ to increase/decrease --- <div style="page-break-after: always;"></div> # III. Making the Relay Work with the Voltage Divider >[!figures] LDR-controlled Relay Module for Automatic Lamp Switching >![[circuit (1).png|center|500]] --- - Turn on voltage (V): 1.807V - Turn off voltage (V): 2.033V - $V_{off}>V_{on}$ makes sense because when going from dark -> light environmental lighting, more voltage is required as resistance is increased