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Author Topic: how do you use resistors?  (Read 1032 times)

liguanmin

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how do you use resistors?
« on: October 12, 2003, 09:26:19 PM »

hi, i am a pretty big newbie at electronics right now even though i am going to be majoring in it. right now i am building a device which will measure wind direction. the wind direction is going to be measure in voltage ranging from 0v (no wind) to about 4.5v. if i started out with 3 D cell batteries (4.5), what kind of resistors would i need to lower the voltage .25 - .20 v? how do you calculate this kind of stuff? thanks for your help ^_^
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viridius

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how do you use resistors?
« Reply #1 on: October 12, 2003, 09:30:04 PM »

You'd use ohm's law V=IR.  Rearraging this to solve for resistance, R=V/I.  This means that the voltage drop (0.25 volts) over the current your device takes (in amps) will equal the resistance in ohms.  Do you have a schematic we can work off of?
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liguanmin

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paintbrush design
« Reply #2 on: October 12, 2003, 09:51:26 PM »




3 D cell batteries go on the left. voltage is output ranging from 0v (no wind) to 4.5v. resistors are going to be arranged in the shape of the unit circle. voltage is output to a lego rcx, which stores voltage at time intervals.
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viridius

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how do you use resistors?
« Reply #3 on: October 12, 2003, 10:33:04 PM »

You could also take a germanium diode and put it in series with the output of your sensors.  Germanium diodes drop the voltage by about 0.3 volts, regardless of current.
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