Issue 103, February 1999
Truck Speed Limiter Control

IMPLEMENTATION

Because fuzzyTECH can simulate the fuzzy-logic system without the target hardware, a fair amount of optimization was accomplished off-line on the PC. Final optimization and verification of the system were conducted on real trucks.

The target system and the MCU for the electronic control unit is mounted in the truck and connected to the development PC (a laptop in the truck’s cabin) by a serial cable. Serial connection enables modification of the running fuzzy-logic controller on-the-fly.

This development technique is efficient because it lets the developer analyze how a certain behavior of the fuzzy-logic controller is caused by the membership-function definition and the rules. And because modifications can be done in real time, the effects can be felt on the truck instantly.

One way to enable on-the-fly debugging is to link the fuzzyTECH real-time remote cross-debugger (RTRCD) module to the fuzzy-logic controller that runs on the MCU and connect it to a serial driver. The RTRCD module consumes about half a kilobyte of ROM, a few bytes of RAM, and some computing resources to serve the serial communication on the MCU.

Because the PIC used in this application can’t provide such resources, the serial debug mode of fuzzyTECH is used rather than the RTRCD module. In serial debug mode, the values of the input variables are sent from the MCU to fuzzyTECH running on the development PC via the serial cable and the results are sent back.

fuzzyTECH shows the entire fuzzy-logic computation in its editor and analyzer windows and enables on-the-fly modifications. To support serial communication, a piggyback board containing a MAX232 driver IC is mounted on the speed-limiter board.

Using fuzzyTECH’s serial debug mode rather than the RTRCD module means that the code size and computation effort previously required for the fuzzy-logic computation on the MCU can be saved and used for the serial communication.

The disadvantage of the serial debug mode is that it computes the system’s results on the PC, where real-time response cannot be guaranteed. Also, unlike the RTRCD module, any crash of Windows, the PC, or the serial communication will halt computation in serial debug mode.