Introduction to the PICAXE Microcontroller
The PICAXE family of microcontrollers is an exciting series of integrated circuits that takes advantage of current technologies to offer a solution that is simultaneously easy, inexpensive, and powerful. Manufactured by Revolution Education, the PICAXE was originally designed for use in schools, but quickly became a favorite among hobbyists. From an automatic plant watering system, to a burglar alarm, to an autonomous robot, the chips are ideally suited for a huge variety of control applications.
In modern life microcontrollers are ubiquitous. Some of the countless common uses include microwave ovens, television remote controls, and the various regulating systems of automobiles. Similar to the microprocessor that powers your personal computer, microcontrollers are a specialized type of integrated circuit or “chip.” They are sometimes thought of as single chip computers because they incorporate circuitry such as timers and memory which are separate components in other microprocessor applications.
Additionally, as their name implies, microcontrollers are optimized for control applications. They will offer an assortment of analog and digital input and output pins. An input pin might interface the device with a simple on/off switch or various sensors measuring environmental variables such as light, sound, and temperature. Output pins are used to send signals to control mechanisms such as relays, lights and motors.
The affordability of the PICAXE system is striking. Current prices for PICAXEs range between about $3.00 to $11.00 US depending on the size and capability of the chip. The software needed to create and upload your custom programs is provided for download at no charge by Revolution Education along with a wealth of manuals and datasheets.
Screeenshot of the free - yet robust - programming software provide by the manufacturer.
There are six different sizes of PICAXE chip available ranging from 8 to 40 pins. The more pins, then the more input and output ports are available. Within the different sizes are additional variations for a total of 11 different chips available as of this writing. The variations offer enhancements such as additional program memory or higher resolution analog ports.
Another key distinguishing feature of the PICAXE is the ability to upload programs to the chip from a personal computer using only a simple serial cable. (For computers that lack a serial port a number of USB converters are available.) Typically a device called a programmer is required to upload to a microcontroller. The PICAXE, on the other hand, is pre-programmed with a bootstrap code which includes the necessary routines to upload directly to the chip.
Revolution Education produces a number of development and getting started packages, and there are also quite a few kits produced by other firms. Although you can certainly spend more, it is possible to get all you need to start programming for under $30. (In fact, if you’re comfortable enough with basic electronics to assemble your own board and you have a computer with a good old fashioned serial port, then all you need is a PICAXE chip, a serial cable, two resistors, and a five volt power supply.)
PICAXE chips are programmed using a very simple structured BASIC syntax. If you have ever used a BASIC programming language before you will find getting started with the environment to be almost effortless. IF…THEN, FOR…NEXT, GOTO, and GOSUB…RETURN routines are supported. Even if programming is new to you, you will likely find the process intuitive once you have worked through a few examples. In addition to the standard BASIC commands, there are a number of specialized commands for microcontroller functionality such as sending control pulses to a servo or sending and receiving infrared signals. As an alternative to learning to write BASIC programs, a flowchart method is also provided.
As you embark on learning to work with the PICAXE you will find that there are extensive online resources available to you. There are a large number of help files included with the free programming software which can be downloaded from www.picaxe.co.uk. There is also a very active PICAXE forum at www.picaxeforum.co.uk. The robot hobbyist site Let’s Make Robots at www.letsmakerobots.com has a large group of enthusiasts with many projects based on PICAXE chips. In no time at all you’ll find yourself coming up with your own ideas and designing your own projects.
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