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I need a circuit to run a tiny motor from a USB port? Answered

I made a leather "Steam Punk" case for a portable hard drive. It has several gears that show under a glass porthole and I need a way to move the gears powered from a second USB cable. I'll use a separate USB cable then the Hard drive as I don't want to compromise the original device. I have a very small motor from some Radio Shack ZipZap RC cars. Tried to design a simple circuit myself but can't get the motor to spin. I suspect it doesn't have enough current. The motor does spin if hooked directly to a AA batery. The ZipZaps work with 2 AAA bateries in the charger/controller. The car hooks on top of the controller charges up and then can run for a short time. Opening the car up it has a 1.2 V 100mAh NI-MH battery inside it. Tried looking at a couple of BEAM robot solar engine designs used to run small motors from solar cells but just coudn't figure out how to convert them.

I'm looking for a small circuit (in size) that could drive this motor, with a backwards current spike protector so the USB or computer doesn't get fried. I have limited EE experience but can through hole solder but not surface mount.



I plan to do something similar... a steam punk usb thumb drive with turning gears with the drive's led (as the drive is accessed)... I am space constrained too... so will use a vibrator motor from a cell phone... I will turn the motor on using an NPN... you can prevent damage to your transistor from motor voltage spikes by placing a diode across the motor... use a potentiometer to set the appropriate voltage for your motor... I'll actually use two diodes in series as the motor I have runs off 3.6V (a friend made a vibrating usb mouse using this method)... hope that helps


A few questions on this circuit. I'm not familiar with all the component symbols here. What does the open triangel after the 10k resistor represent. On the same resistor what is the filled triangle pointing back to it? Is this just a 10k potentiometer? Also the 1 K resistor is just floating, is something missing? It looks like this might be where you were going to connect the LED as the trigger to turn on the NPN. In the circuit you describe are you using the series diodes just to drop the voltage? One last question. Is the protection diode on the motor a standard or zener? I am guessing standard but the line could be squiggly.

No matter how many times I read what some of these componets do it doesn't seem to stick in my head enough like it should to use them. I'm slowly beating electical knowledge into my brain no matter how much it resists.

Thanks for your time on this. I definitely want to see your thumbdrive when done. It sounds great.

Hi again... yes, it's just meant to be a pot... however, 10K would be fiddly to use 1K would be better to adjust the voltage... I'm not using a pot. as I'll drop the voltage with 2 diodes (0.7Vx2=1.4V giving my 3.6V)... a general purpose diode like the 1N4001 will be fine (sorry about my circuit drawing)... when using a device with a coil (motor, relay etc)... there is a brief induced high voltage over the coil when it's switched off (due to the collapsing magnetic field). The backwards diode helps the induced voltage to drive a current through the coil & diode so the magnetic field dies away slightly slower than instantly...

Yes, again sorry for my circuit... I'll be pulling the base high using 5V... the thing to remember about transistors is...

With an NPN: If voltage of base is higher than the emitter, current flows collector->emitter.
With a PNP: If voltage of base is lower than the emitter, current flows e->c

I'd steal some juice of the existing supply if I were you, because the system will have asked for a full allocation of power already for you. Do you want this thing to be permanently powered ?


I don't want to destroy or maim the original hard drive or cord. With the second cord I can always unplug the "useless" cord if I'm out of USB spots somewhere. Of course I'm also wiring in a switch. The gears may sound anoying after a while, without getting it to move I don't know how noisy it will be yet. This also allows swapping of the harddrive as I have a couple of the same drive. It would be nice to have the full 500 negotiated mA. Another issue I would be worried about is it is not a powered drive and it doesn't have a multi-end connector on it.

I'd solder my connection directly on the USB connectors power pins.