When you want to connect a motor up to an Arduino or other microcontroller, the natural response is to reach for an H-bridge chip. Granted, that's exactly what an H-bridge is for - but it's possible to achieve the same result using a simple custom circuit based around low-cost NPN transistors, as demonstrated by Tanmay Deuskar in his latest Instructable.
Based on the readly-available and low-cost BC-547 NPN transistor, a pair of 1K Ohm resistors, two capacitors, and incidental components including headers and a 9V battery, Tanmay's circuit is simple and affordable. While it isn't as feature-packed as an H-bridge - it can only run motors in a single direction, where an H-bridge can run them forwards or backwards as required - it's certainly usable for projects where the extra complexity of an H-bridge isn't required.
Tanmay's project walks the reader through wiring everything up on a solderless breadboard to check it all works, then goes a step further by demonstrating how to transfer it to perfboard. For those who haven't used perfboard before, it forms a middle stage between solderless prototyping and printed circuit board creation: components are inserted through the holes in the perfboard then soldered into place, with solder blobs or jumper wires making connections as required and existing electrically-connected strips - if present on the type of board you've chosen - being cut if necessary.
In this Instructable I'm going to show you how to make a motor driver board using transistors which can power two motors. This motor driver board will be able to operate the motors only in one direction, but would be cheaper than an H-bridge (E.g. For me, H-bridge would cost about Rs 150+ , whereas I could make this board in about Rs 30); and more importantly it's fun to do it.