FEBRUARY 7, 2011 (See also Companion Blog )
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The purpose is to test the potentiometer effect on LED brightness, voltage, and motor speed. None of the various texts I've read explain the parallel, if any, between variable voltage and the effect of Pulse Width Modulation (PWM). I prefer to test the analog portions and components first.
Theory:
The pot (potentiomenter) should vary the voltage in the circuit, the brightness of the LED, and the speed of the motor. The circuit shows that potentiometer is in a position to vary the electric flow to the three components, the LED, the Voltmeter, and the motor. All segments of the circuit should be affected by the same changes.
Practice:
The voltage and LED did vary as predicted, but not the motor speed. Here is the measured effect of various resistor values in series with the voltmeter. The pot is not labeled, but I believe it goes from 0Ω to 10,000 Ω. I still include the static resistor, a holdover from having burned out too many LEDs.
The table here is not pretty, but for some reason, this blog inserts a blank page of white space when I try to use table tags. (If you know the easy way to correct this, email me.)
Fixed Resistor Low Range High Range
330Ω 1.68V 1.88V
1000Ω 1.68v 1.80V
4700Ω 1.67V 1.72V
9400Ω 1.66V 1.69V
Conclusion:
Turning the pot seems to vary the voltage in the LED segment of the circuit between very narrow limits. I note that the LED never did go out completely. The motor, however, was not at all behaving as expected. It ran at a constant speed or not at all throughout all pot settings. As the pot was the only variable here, I connected the pot and motor to the battery itself. This produced the same constant motor speed as without any resistance.
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