In How Electronic Gates Work, you learned about 7400-series TTL devices, as well as where to buy them and how to assemble them. What you found is that it can often take many gates to implement simple devices. For example, in the digital clock article, the clock we designed might contain 15 or 20 chips. One of the big advantages of a microcontroller is that software -- a small program you write and execute on the controller -- can take the place of many gates. In this article, therefore, we will use a microcontroller to create a digital clock. This is going to be a rather expensive digital clock (almost $200!), but in the process you will accumulate everything you need to play with microcontrollers for years to come. Even if you don't actually create this digital clock, you will learn a great deal by reading about it.
The microcontroller we will use here is a special-purpose device designed to make life as simple as possible. The device is called a "BASIC Stamp" and is created by a company called Parallax. A BASIC Stamp is a PIC microcontroller that has been customized to understand the BASIC programming language. The use of the BASIC language makes it extremely easy to create software for the controller. The microcontroller chip can be purchased on a small carrier board that accepts a 9-volt battery, and you can program it by plugging it into one of the ports on your desktop computer. It is unlikely that any manufacturer would use a BASIC Stamp in an actual production device -- Stamps are expensive and slow (relatively speaking). However, it is quite common to use Stamps for prototyping or for one-off demo products because they are so incredibly easy to set up and use.
They are called "Stamps," by the way, because they are about as big as a postage stamp.
The specific BASIC Stamp we will be using in this article is called the "BASIC Stamp Revision D".
The BASIC Stamp Revision D is a BS-1 mounted on carrier board with a 9-volt battery holder, a power regulator, a connection for a programming cable, header pins for the I/O lines and a small prototyping area. You could buy a BS-1 chip and wire the other components in on a breadboard. The Revision D simply makes life easier.
You can see from the previous table that you aren't going to be doing anything exotic with a BASIC stamp. The 75-line limit (the 256 bytes of EEPROM can hold a BASIC program about 75 lines long) for the BS-1 is fairly constraining. However, you can create some pretty neat stuff, and the fact that the Stamp is so small and battery operated means that it can go almost anywhere.