Saturday, September 15, 2018

The Arduino before the Arduino: Parallax Basic Stamp

I recently had cause to dig down through the layers of strata which have accumulated in my electronics bin. In one of the lower layers I found this bit of forgotten kit: the Parallax Basic Stamp II. This was the Arduino before there was an Arduino, a tiny microprocessor aimed at being simple for hobbyist and low-volume commercial use.

The Basic Stamp line is still sold today, though with designs developed over a decade ago. The devices have enough of a market to remain in production, but are otherwise moribund. The past tense will be used in this blog post.

The Basic Stamp line dates back to the early 1990s. The Basic Stamp II shown here was introduced in 1995. It used a PIC microcontroller, an 8 bit microprocessor line which has been used in deeply embedded applications for decades and is still developed today. The PIC family is a product from Microchip Technology, the same company which now supplies the AVR chips used in the Arduino after acquiring Atmel in 2016.

The PIC contained several KBytes of flash, which held a BASIC interpreter called PBASIC. An external EEPROM on the BS2 board contained the bytecode compiled user BASIC code. Though it may seem an odd choice now, in the early 1990s the choice of BASIC made sense: the modern Internet and the Tech industry did not exist, with the concordant increase in the number of people comfortable with developing software. BASIC could leverage familiarity with Microsoft GW-BASIC and QBASIC on the PC, as MS-DOS and Windows computers of this time period all shipped with BASIC. Additionally, Parallax could tap into the experience of the hobbyist community from the Apple II and Atari/Commodore/etc.

' PBASIC code for the Basic Stamp
LED         PIN 5
Button      PIN 6    ' the BS2 had 16 pins
ButtonVal   VAR Bit  ' space is precious, 1 *bit* storage
LedDuration CON 500  ' a constant

' Init code
INPUT  Button

 ButtonVal = Button                 ' Read button input pin
 FREQOUT LED,LedDuration,ButtonVal  ' PWM output to flicker LED
 PAUSE 200                          ' in milliseconds

PBASIC supported a single thread of operation, the BASIC Stamp supported neither interrupts nor threads. Applications needing these functions would generally use a PIC chip without the BASIC interpreter on top. Later Stamp versions added a limited ability to poll pins in between each BASIC statement and take action. This seemed aimed at industrial control users of the stamps, for example Disney used BASIC Stamps in several theme park rides designed during this time frame.

A key piece of the Arduino and Raspberry Pi ecosystems is the variety of expansion kits, or "shields," which connect to the microprocessor to add capabilities and interface with the external world. The ecosystem of the BASIC Stamp was much more limited, suppliers like Adafruit were not in evidence because the low volume PCB design and contract manufacturing industry mostly didn't exist. Parallax produced some interesting kits of its own like an early autonomous wheeled robot. For the most part though, hobbyists of this era had to be comfortable with wire-wrapping.