What resistors/transistors/capacitors would I need to connect a standard 1.5V motor (from radio shack or the like) to a BOE's 5V supply? Or what else could I do to use the BOE to power the Motor?
I took a look at the PDF file that Jon recommends.· All very good, but it really misses the point of a 1.5 volt motor on a 5.0volt [noparse][[/noparse]or higher supply]
The basic fact is that too much voltage will harm the motor.· I do suspect that a 1.5 volt motor is really a 1.5volt to 3.0 volt motor. So, you may have a big margin of safety.
So how does one reduce the voltage?· There are several ways and some are more efficent than others.·
[noparse][[/noparse]1] One way is to merely insert a resistor in series with the motor to reduce the voltage and limit the current.
[noparse][[/noparse]2] Another way is to use diodes to cause a voltage drop.
Both·[noparse][[/noparse]1] and·[noparse][[/noparse]2] assume that the motor does NOT draw enough current to harm the BasicStamp.· I think about 20ma is the limit.
[noparse][[/noparse]3] You could use a transistor to turn on and off the motor.· The transistor would drop the voltage 0.7 volts by itself.· Additionally, you could insert a resistor or several diodes to get the voltage down to 1.5 volts.· This allows you to use a motor that draws more than 20ma current.
[noparse][[/noparse]4] You could also use an H-Bridge (For a starting point, I strongly recommend the six-transistor 'Tilden'·H-bridge·that BEAM robots use.· It is cheap and designed for such small, low-voltage DC motors).· You can Google 'Tilden H-bridge' to find it.· With all those transistors, I believe the voltage drop is 1.4 volts and that may be enough for your motor.· If not, you can always insert a resistor near the motor, but not a diode[noparse][[/noparse]as this is an H-bridge that reverses the polarity].
Having said all that, I am sure there are some engineers out there with cleaner, more elegant solutions.· But, the above is a very good, cheap entry for a hobbyist.· good luck
Comments
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Jon Williams
Applications Engineer, Parallax
Dallas, TX· USA
I took a look at the PDF file that Jon recommends.· All very good, but it really misses the point of a 1.5 volt motor on a 5.0volt [noparse][[/noparse]or higher supply]
The basic fact is that too much voltage will harm the motor.· I do suspect that a 1.5 volt motor is really a 1.5volt to 3.0 volt motor. So, you may have a big margin of safety.
So how does one reduce the voltage?· There are several ways and some are more efficent than others.·
[noparse][[/noparse]1] One way is to merely insert a resistor in series with the motor to reduce the voltage and limit the current.
[noparse][[/noparse]2] Another way is to use diodes to cause a voltage drop.
Both·[noparse][[/noparse]1] and·[noparse][[/noparse]2] assume that the motor does NOT draw enough current to harm the BasicStamp.· I think about 20ma is the limit.
[noparse][[/noparse]3] You could use a transistor to turn on and off the motor.· The transistor would drop the voltage 0.7 volts by itself.· Additionally, you could insert a resistor or several diodes to get the voltage down to 1.5 volts.· This allows you to use a motor that draws more than 20ma current.
[noparse][[/noparse]4] You could also use an H-Bridge (For a starting point, I strongly recommend the six-transistor 'Tilden'·H-bridge·that BEAM robots use.· It is cheap and designed for such small, low-voltage DC motors).· You can Google 'Tilden H-bridge' to find it.· With all those transistors, I believe the voltage drop is 1.4 volts and that may be enough for your motor.· If not, you can always insert a resistor near the motor, but not a diode[noparse][[/noparse]as this is an H-bridge that reverses the polarity].
Having said all that, I am sure there are some engineers out there with cleaner, more elegant solutions.· But, the above is a very good, cheap entry for a hobbyist.· good luck
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G. Herzog in Taiwan
Post Edited (Kramer) : 5/12/2005 4:12:32 PM GMT