Boost Regulator with microcontroller

[timmmmeh]

Hi guys, I need some help with my circuitry.  For my project I am working on controlling a linear actuator.  The actuator needs 12V and 3amps to run at its max speed.  However, the HC12 microcontroller only supplies 5Volts (not sure about the amoutn of current).  Anyway, I was thinking about using a boost regulator circuit but then that would limit my current.  Is there a better and more efficient way to step up the voltage and current so i can control teh actuator through the microcontroller?  Thank you in advance for any help.   

[robot321]

Have the micro controller drive a relay which has the current you require.

[dunk]

sounds like you need a mosfet:
http://www.societyofrobots.com/electronics_advanced_components_tutorial.shtml#mosfet

mosfets are fine for a simple on/off but if you want controll of a motor forwards/stop/backwards you might want to look for a motor controller ICs. motor controllers are made from several mosfets.
try doing a few searches for "mosfet" and "motor controller".

dunk.

[timmmmeh]

I am using the microcontroller to control to control the direction and speed (PID controller) of the actuator.  Does anyone know how I can go about stepping up the 5volts from the microcontroller to 12Volts and have about 3amps?  Also, are these motor controller ICs just H-bridges and transistors because they seem quite expensive. 

[Admin]

I am using the microcontroller to control to control the direction and speed (PID controller) of the actuator.  Does anyone know how I can go about stepping up the 5volts from the microcontroller to 12Volts and have about 3amps?

What you actually want to do is use a ~12V battery to power your motors, and then step that down with a voltage regulator or switching regulator. You can also use two different batteries - a 6V for your microcontroller and a 12V for your motors. I say 6V because you should always use a 5V regulator with your microcontroller.

Also, are these motor controller ICs just H-bridges and transistors because they seem quite expensive.

yeap. i think the prices will come down a lot in the next 5 years . . . they are way cheaper now then when i first started making robots!

[timmmmeh]

A brief summary of my project:  I am building the self-leveling part of my robot.  For the inputs, I am detecting the balance with an accelerometer.  If the accelerometer senses a tilt then it'll tell the actuator to move up or down. 

When I discussed it with my professor, I said that I was going to use a relay and just hook up 12Volts to the relay and use the microcontroller as a switch to control the relay (on or off).  However, my professor said that it won't be a stable system because it'll oscillate too much because it's a bang bang control.  So, he told me to look into a PID control system.  I thought my solution would work at first, but i'm just lost right now.  Can anybody steer me into the right direction or give me some more pointers?  Thank you in advance.     

[Admin]

well it wont work for another reason too - microcontrollers dont have enough power to actuate a relay. the response rate of a relay is pretty slow, too. you could use a motor driver or H-bridge and that will allow PID.

i recommend using a servo instead, as they are perfect for PID control systems plus they are ultra cheap and simple.

[timmmmeh]

I want to step up the output of the microcontroller (5V) to 12V and be able to supply at least 3amps.  Can anyone recommend me a solution and/or a site that's relatively cheap?  Thanks

[JonHylands]

Your professor is correct. You will be very frustrated trying to do this with a relay.

What you need is an h-bridge. something like this:

http://www.robotshop.ca/home/products/robot-parts/electronics/motor-controllers/pololu-high-current-motor-driver.html

You can hook that directly between your micro-controller and your motor, and you can control the motor speed directly if your micro-controller can do PWM.

- Jon

[timmmmeh]

For the H-bridge, we can just build taht with simple transistors right?  The problem that i'm mostly concerned with is the voltage and the amperage.  What would be the neatest and most cost effective way of stepping up the voltage from 5v to 12v?

[JonHylands]

You can build it easily with MOSFETs. I personally wouldn't try and build a 3 amp h-bridge using transistors.

- Jon

[Brandon121233]

first of all just as a side note you said that it would be controlling tilt

A brief summary of my project:  I am building the self-leveling part of my robot.  For the inputs, I am detecting the balance with an accelerometer.  If the accelerometer senses a tilt then it'll tell the actuator to move up or down. 
 

would'nt it be better to use a tilt sensor instead of an accelerometer?
seccond of all your not really "stepping up" the voltage your just controlling the voltage from the battery with the microcontroller, the easiest way to do that is just to use a simple H bridge IC, there are many out there that are rated to supply 3A of current, just be sure to put a heat sink on it. You can get these H Bridge IC's for free as samples from many companies which is an added bonus.