Friday, 24 September 2010

DC Motor Driven by Arduino

At last, I've mustered up the courage to hook up a DC motor to the Arduino!

The reason that it's a big deal is that you can't connect a DC motor directly to the output pins on the Arduino - it'll draw too much current and fry the Arduino chip.  This method uses a transistor to switch the large amount of motor current with a small amount of 'control' current.  As an added level of safety for the Arduino, I've also use an Opto-Isolator which a means of completely separating the two circuits - control and output.  Unless I do something silly (!), the Arduino should be safe.  (I already fried one transistor in testing because I'd forgotten to put a diode across the back end of the motor!)

BIG respect and thanks to Mike Cook for his excellent article on hooking up motors.

My circuit diagram is a hacked together version of a couple of his diagrams.
(used with permission - thanks Mike)

The immediate application is for driving the blades on our learning project GRZR - the robot mower!

Thursday, 16 September 2010

Lemon and Potato Battery!

Today we made a battery out of Lemons and Potatoes!

This came about from the question "What is electricity?"  I had suggested that electricity is not a source of power... ie. you can't go dig up some electricity out of the ground!

John's smart reply was "of course not, it grows on trees!"   (I like his sense of humour)

We all laughed because that's nonsense.   Right?

So, this week, we made electricity from Lemons and Potatoes.  (thanks Dad)

Harvey and John wired the four together with copper and zinc (galvanised) nails inserted into the ends of each fruit/veg.  The lemons made 0.9V whereas the potatoes produced about 0.6V

In all we had about 3.5V which was enough to light up some of the LEDs we had on hand — albeit dimly!

Conclusion — Electricity is the MOVEMENT of electrons.

We also learned that these electrons move VERY slowly... like the minute hand on a clock, but their 'effect' happens at almost the speed of light!!