insideGadgets

I’ve finally got around to wiring up my 8×8 LED Matrix and now it’s time for some fun with it. Though out playing with this I’ve learnt about shift registers and how we can use them along with a transistor array chip.

First things first, have a read and look through the Arduino’s ShiftOut guide as they are very well put together (keep re-reading it if it doesn’t make sense): http://www.arduino.cc/en/Tutorial/ShiftOut

To summarise the guide:

• A shift register allows you to have 8 outputs while only using 3 pins on the Arduino
• You send a byte to the shift register which has 8 bits (e.g. 10010000)
• You can combine shift registers so instead of having only 8 outputs you can have 16 when using 2, 24 when using 3, and so on
• When combining shift registers, instead of sending out the 8 bits to the first register and 8 to the second register it’s actually reversed, so the first 8 bits you send are actually for the second register and the next 8 bits go to the first register

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I bet you were expecting to see Part 3 of this build? I’ve recently learned about the important of power dissipation when giving my circuit the real test of 12 volts @ 0.75 Amps and thought I’d share it with you.

In my selection of transistors for the motor controller I went with ones that firstly had a low Vce and then based on price after that; what I didn’t completely take into account is the power dissipation of these components. I know I mentioned it in part 1 however I didn’t completely understand why one of my transistor’s datasheets had 2 values for power dissipation… and now I do, and you will to!

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Following on from Part 1, we’ve done our design and now it’s to put our prototype to the test, this will post won’t be as long as the design because all we need to do is test.

This is how our circuit looks to power 1 motor in 1 direction only.

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So here we are, we’re going to build us a motor controller to control 2 motors in both directions. First we’ll start off with our design which shows how our components will be connected and our reasoning, we could of just bought a motor controller chip like the L298N but we will rather learn something from our build and it should be easier to use than the L298N chip. Another on the plus our motor controller will have is about 1/2 the Vce of the L298N which is an advantage when dealing with low voltage motors and low voltage power supplies as well as back EMF protection (both will be explained).

This is quite a long post and do remember that I’m also new to understanding all of these concepts so do feel free to correct me if I’m doing something wrong! I’ve spent a good month checking all this out, posting on an electronics forum and trying to grasp the concepts I’ll be explaining you.

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So we’ve got our parts and our motor controller so we are now ready to make this robot move forward, backwards and turn. I’m assuming you’ve put the wheels on the motors, mounted them to your design, used a gearbox if necessary and you do have a motor controller. Plus you also have the 9 volt battery and clip for Arduino.

In this part we will need:

• Arduino Duemilanove ATmega328
• 4 x NPN general transistors (e.g. PN100, PN2222)
• 4 x 6.2K Ohm resistors (10K will do fine too)
• Breadboard
• Some wire

Example Schematic below

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I’ve decided to make the next project that just about every person exploring electronics does… the making of a small robot. In my case, I’ll be using the Arduino to control the robot which will just be a robot that can avoid walls that  I might build more functionality in the future.

The first part of the project is to acquire the necessary parts such as motors, gears, wheels, infrared sensors, etc. Luckily for me, I actually had a robot that I was building up before; it’s the Cycbot from RealRobots (for anyone who might remember it). I got around to issue 6 or 7 and eventually gave up on it. I do however have the motors, gears, wheels and the motor controller, so it’s all actually working, it just goes forward for now.

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