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Microcontroller Motor control help

Josh Kay

Oct 30, 2014
8
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Oct 30, 2014
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Hi Guys, I have what I question, I have a Micro-controller that is capable of putting out 5mA I need to control a very small motor that draws 15mA running and if it hits limit it gets up to about 50mA. I am told that the person has capability to output a positive or negative voltage. Which means I don't even need a polarity changing circuit I just need a small current increase. I thought I had it figured out using a fet but than I realized the FET needed a + control input and the negative input didnt work.
 

Anon_LG

Jun 24, 2014
453
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Jun 24, 2014
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453
The part about a person outputting a voltage :confused: The voltages gave off by a person constantly fluctuating and can not be used to power your motor (unless you have access to some obscure method). I would suggest you feed the output from your micro controller into the base of a bipolar NPN transistor. The NPN transistor acts as an electronic switch. Are you experienced with electronics, if yes then you will know how to set up this circuit, if not then you should look around the forum and at some of the resources. I hope this helps.
 

Josh Kay

Oct 30, 2014
8
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Oct 30, 2014
Messages
8
Ok I was using the MOSFET as a switch but maybe I'm just overthinking at this point but the switch circuit works perfect when a positive 5v was outputed to the base of the fet the problem is when they change it to a negative 5 volt output (to reverse) it didn't work because I wasn't actually sending -5v to the motor I was sending it to the fet and the polarity of the motor was the same. That's why I am trying to figure out if there is a device that will take whatever I give it +5 or -5 and and just up the current to the 15-50ma I need . I know an h bridge is used for motor control but that requires an enable . I only have 1 channel available which can output either a +5v or -5v but is only capable of 5ma not 50ma
 

Anon_LG

Jun 24, 2014
453
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Jun 24, 2014
Messages
453
You had not explained clearly what you were trying to do in the first message. As I understand it the microcontroller output can supply 5ma, and you want to be able to make the motor go one way and be able to reverse however the motor needs 50ma. Is this what you mean?
 

BobK

Jan 5, 2010
7,682
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Jan 5, 2010
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7,682
Ok I was using the MOSFET as a switch but maybe I'm just overthinking at this point but the switch circuit works perfect when a positive 5v was outputed to the base of the fet the problem is when they change it to a negative 5 volt output (to reverse) it didn't work because I wasn't actually sending -5v to the motor I was sending it to the fet and the polarity of the motor was the same. That's why I am trying to figure out if there is a device that will take whatever I give it +5 or -5 and and just up the current to the 15-50ma I need . I know an h bridge is used for motor control but that requires an enable . I only have 1 channel available which can output either a +5v or -5v but is only capable of 5ma not 50ma
Look up H-bridge. This is a circuit that allows you to reverse polarity to a motor. It requires 4 switches, (MOSFETs or BJTs), If the motor is running off the same voltage as the microntroller, all you need is 2 P-channel and 2 N-channel MOSFETS.

You can also buy chips for this purpose. The L293 is a popular one, though I do not like it because it uses BJTs, which drop too much voltage in use.

Bob
 
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