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SPLat Controls microPLCs Despite what you might have heard, world-class electronics is still produced right here in Australia. If you’re manufacturing a product that needs an electronic control module, then SPLat Controls, a local company in Seaford, Victoria, can probably help. By PETER SMITH S PLAT CONTROLS produce a range of Programmable Logic Controllers (PLCs) designed specifically for the OEM market. They boast very low start-up costs, simple expansion and easy programming. A custom design service is available, or you can build up your system from one of the standard off-the-shelf designs. What’s a PLC? PLCs provide the automation “engines” for industrial process monitoring and control. They’ve been around since the late 1960s, originally replacing complicated and unreliable banks of electro-mechanical relays. Today, PLCs are used in TOP OF PAGE: As shown here, the MMi99 microPLC is also available as part of a sales demonstration kit. It’s set up to simulate simple machine control, complete with LCD display, thermistor temperature sensor and appropriate front panel graphics. Companion software (supplied on CD) demonstrates the MMi99s serial communications capabilities. 68  Silicon Chip everything from industrial washing machines to full-blown discrete parts manufacturing lines. Minis to micros The earliest PLCs to use general-purpose computers for “back-end” processing were based on the DEC PDP-8 minicomputer. Not surprisingly, many times more computing power is now available in microprocessor-based systems at a tiny fraction of the cost. All design-in (embedded) PLCs now use microcontrollers (or similar technology) for their processing elements. Microcontrollers integrate a microprocessor core with many of the peripherals needed in a typical PLC. To get a feel for the technology, let’s have a look at one of SPLat Control’s offerings, the MMi99 microPLC. MMi99 microPLC The MMi99 consists of a single PC board, measuring just 88 x 127mm. At the heart of the board is an 8-bit Motorola MC68HC908 microcontroller running SPLat’s proprietary programming language. The board interfaces to the outside world via a series of I/O (input/output) ports, terminated on rows of push-on connectors. Included are two analog inputs, two analog outputs (both 8-bit), eight digital outputs (open collector) and eight digital inputs. Both analog inputs can be configured to measure voltage, current or resistance, thus allowing direct temperature measurement using low-cost thermistors. Five push-button switches and seven LEDs mount on the opposite side of the board, forming part of an in-built operator interface. This arrangement allows for direct mounting to an aluminium faceplate. A piezo “beeper” and connector for several popular liquid crystal display modules completes the interface. A universal graphics overlay is available to suit the faceplate, making it possible to quickly assemble a “proof of concept” or one-off design. On-board regulation means that the board can be powered from any 12 28V DC supply with around 200mA www.siliconchip.com.au A shot of the MMi99 mounted on the aluminium faceplate. The LCD module at the top is wired to the main board via ribbon cable. The input and output ports are terminated in rows of connectors along the top and bottom of the board. A D-9 connector is provided for RS232 (PC, modem, etc) communications. Connectors at the left and right sides are for expansion purposes. capacity. Our review unit was supplied with a 12V DC 500mA plugpack. Programming As with all of SPLat’s boards, the microcontroller on the MMi99 is programmed with a proprietary language designed specifically for PLCs. The high-level nature of this language means that it should be relatively easy to learn. Controller programs are first written and simulated on a PC before being translated into a more compact form and uploaded to the FLASH memory in the MMi99’s on-board micro. An RS232 port is provided on the board for the PC connection. This port can also be used for field updates, either via direct or modem connection. The SPLat language contains a repertoire of over 200 instructions. For simple applications, however, you have the option of using a subset of the language called “Fast-track”. With www.siliconchip.com.au only 14 basic instructions to learn, PLC programming surely doesn’t get any easier! Expansion For more demanding applications, the MMi99 can be expanded both in terms of I/O capability and functionality. Two on-board connectors are provided for this purpose. The first of these is intended for connection to “SPice” add-on boards. The SPice interface provides a means of adding low-cost application-specific circuitry to the MMi99. For example, a typical SPice board might contain circuitry to condition the output of a sensor before it is fed into the MMi99 processor. The second connector is designed for more sophisticated peripherals. SPLat Controls call this the “SPx” interface and it utilises an enhanced version of the industry-standard “SPI” serial bus for communication. An ex- ample of an off-the-shelf SPx board is the XIRO16, which adds eight digital inputs and eight relay outputs to the MMi99. Going custom The simple expansion system that SPLat Controls have incorporated in the MMi99 means that it shouldn’t cost the earth to add capabilities to a basic system. Once a working system is proven, the results can be built as a complete custom controller, if quantities demand it. And the good news is that your programming investment remains intact, thanks to the high degree of hardware abstraction that’s part of this system. More information The MMi99 is available as a board on its own or as part of a developer’s kit complete with front panel, LCD display, graphics overlay and software/ documentation on CD-ROM. Detailed information on SPLat Controls products can be obtained on-line at www.splatco.com.au You can also reach them by phone on 03 9773 5082 or e-mail to sales<at>splatco.com.au SC December 2003  69