[Robotgroup] Generator info for Sam

[Paul Atkinson]

I think a 100 Ohm resistor or anything in the range up to 220 Ohm will work,
adding a capacitor (100uF to 1000uF) might help make the voltage more
steady. Perhaps if you bring the pieces and the motor with the 5V output, we
can help.

The formula for the resistor is (Vmotor-Vled)/0.02 = R
Where Vmotor =5V, Vled=3V (approx for White LED), 0.02 is 20 milliamps
(expressed in Amps as 0.02) and solve for R in Ohms. So 5-3=2, 2/0.02=100,
R=100 Ohms.

Paul

On 8/30/07, thecomers at juno.com <thecomers at juno.com> wrote:
>
> I pulled out one of the gear motors from my Mindstorms 1.0 set. It is this
> motor:
>
> http://www.legoeducation.com/store/detail.aspx?KeyWords=motor&by=20&ID=453
>
> This is a 9 volt DC gear motor. I hooked a voltmeter to the terminals,
> gave the output shaft a spin, and was able to generate 5 volts. If I could
> get a good spin on the motor, I probably could have gotten a higher voltage
> (maybe 6 or 7 volts).
>
> Then I hooked up a high-intensity white led directly to the terminals of
> the motor and spun the output shaft slowly. I was easily able to light the
> led for a fraction of a second. I did not try to give it a hard spin because
> 5 or 6 volts might burn out the led. To protect teh led, you might want to
> add a resistor in series to the circuit. There are calculators on the web to
> calculate the value of the resistor you need, or someone can show you how to
> do the calculation.
>
> Thanks,
> Bob Comer
>
>
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