“Supplying power to motors and LEDs is not always just a case of connecting to a battery and flicking a switch. Sometimes we need to control the speed of motors and be able to dim LEDs for a romantic mood effect, which is often achieved by pulsing the motor / LED with a voltage at a specific frequency (PWM). If we tried to run the motor directly off a PWM pin on an Arduino we would soon smell the tale-tale scent of burning silicon and maybe even see a small flame being emitted, which is obviously a bit of a fire hazard! The controller needs to not only pulse the motor windings with the Arduino, but also needs to bring current in from a fairly robust auxiliary power supply. This is achieved by using a set of 4 integrated circuits containing power transistors, resistors and diodes, all in contained within the four neat little packages. A manually controlled lighting system is great for setting moods, where you can get exactly the right lighting level for a romantic evening, but stepper motors have some seriously useful applications and to be able to control them manually, without using a computer, effectively gives you an incredible level of precision control, quite literally, at your finger tips. Some engineering and medical jobs need to be done on a high precision microscopic level. Maybe you want to accurately place miniature components on a circuit board or perform a high precision surgical operation or experiment with genetic engineering under an electron microscope? Some jobs are just too small and delicate to be done by hand without assistance from a machine. For example, this controller could move a surgeon’s scalpel to 1/100 th of a mm accuracy (or better) using your fingers. But the best thing of all is that it’s incredibly easy to build - A reasonably clever 12 year old would have no problems building this controller - perfect for any budding brain surgeon! There are no SMT components to solder, no complicated programming, no software drivers to drive you crazy - just a few cheap components, most importantly the STMicroelectronics L293E, and an Arduino Mega or Due. Just because this design is simple does not mean that it’s not incredibly useful. It can be used to control a16 channel lighting system with a honking great 1A per channel - yes that’s 16A total - and as a general purpose slider / rotary pot / toggle switch / push button Arduino interface and for precision control of stepper motors. So, the next time you go in for a frontal lobotomy, your surgeon may well be using one or two of these controllers and a couple of Arduinos to not only do the surgical operation but also to control the mood lighting for a nice relaxing environment!”