Simple 2-way motor control for the arduino

When I say simple, I don't mean use a speed control. But control the motor directly without any external circuitry. Here's how:

How this came about:
I recently was working on an instructable about charlieplexing with an arduino. And I was wondering if the same principle would work with motors to some extent. So I came up with the idea that if you used a motor instead of an led you could have 2-way control of it & if you used 2 PWM (Pulse Width Modulation) ports you could have 2-way variable speed control for a motor with no external hardware!! So I decided to post my findings. Have fun! If you have any questions Please ask them.

Note: This is not the safest way to control a motor. Each I/O pin can only handle 40 mA of current. I would recommend using a H-Bridge as pointed out by: Bongmaster & Frollard.

I am not responsible for any thing bad that happens to you or to your arduino!

Step 1 The stuff you need:

Parts:
- Arduino
- Small DC motor
- Wire for motor

Tools:
- Computer with Arduino IDE installed
- A-B USB cord

Comments

[Eonir]

The power limits of the microprocessor are not the only thing you should be worried about.

A motor is not an entirely resistive object. It has also some inductance. What does that mean? It means that when you reverse the voltage on the pins, the current doesn't change its direction immediately. So, for a short moment, the motor acts like a current source.

And that could effectively blow up your microprocessor.

[Eonir]

I didn't have time to check your code, but there's one thing you can do to prevent a hot situation. Whenever you want to switch your motor, a dead time would be applied, in order to allow for the current to fall to a negligible level.

[uberdum05]

Or just slowly ramp the motor speed up and down

[shortcircuitaz]

I tried this and my motor must be too big or something.. do I need to send any information through the interface to the controller?

[wfelix]

very good for small motors... '

but, for big motors, use analog io or gnd+digital with an external driver is better (obviously)''

but, yet, is a great idea

[GitarGr8]

Just so you know, there is an extremely large voltage that is created when the magnetic field of a motor breaks down, ie. when you switch off the circuit. You can visually see this if you hook up a 9V batter to the motor and slowly remove a lead. The spark that is created means a LOT of volts (someone smarter than I could tell you an exact number) which WILL damage / destroy the transistors in your chip. You can get around this by using a protection diode, which will dissipate that voltage back through the coil:

http://www.kpsec.freeuk.com/trancirc.htm
(scroll down to protection diode)

[kyle brinkerhoff]

OR! you could just buy a pwm motor controller and drive FLIPPEN HUGE MOTORS!

[the_burrito_master]

Try a couple transistors as amplifiers.

[beehard44]

or relay?

[the_burrito_master]

uh yeas.

[Chowmix12]

check out STM, they have free samples for an l298HN IC, which is an ic that incorporates 2 h bridges inside the IC.

[BrunoG]

cool.

[daltore]

It seems to me like this would only be able to drive the motors at a maximum of 1/2 power each when they're reverse of each other.  You could get both to move full-power when they're going the same direction (they share either a common ground or common source), but when they're opposite, you're spending 1/2 of each PWM train on each motor (which at full power, is a 1/2 duty-cycle PWM wave).  Interesting idea though, it's crazy what you can do with microcontrollers these days.

[Bongmaster]

kool but its best not to drive a motor directly from an arduino ;) could blow ure pins..

u can make a simple h bridge from transistors like i did here
http://bongmasters-things-and-stuff.blogspot.com/2009/05/robot-h-bridge-pair-motor-driver.html

using the schematic on this page
http://www.beam-online.com/Robots/Circuits/circuits.html

there was a 4 transistor version somewhere too. cant remember where tho XD

[computergeek]

 I'm glad you like it! It is definitely not the best way, but probably the simplest. You do have to be careful using this approach.

[Bongmaster]

hell yea XD i did it this way 1st XD but i didnt want to blow my chip by drawing the current thu it to drive a motor :)

hence why i built the h-bridge pair i linked ;) better safe XD

[frollard]

Drawing current and especially drawing a changing current (like pwm) thru an inductive load like a motor can have disastrous results to those little pinnies :P

Totally agreed in using an h-bridge, driven by these pins.

[computergeek]

 I looked at the Arduino Specs, and found each I/O pin can only handle 40 mA of current. I measured the current draw of my motor & found it was at the max 35 mA's. So I decided to put a warning in my instructable. Personally I prefer continuous rotation servos over motors.

[frollard]

Remembering when a motor turns on or off it has a pulse of very high inrush current to get it started.  A multimeter will probably not even detect it because its so fast - but its enough to destroy a pin.

using pwm just means you're turning it on and off MANY times...more risk of burning out that expensive pin....my 2 cents.