Ruggedised PIC control systems upgrade the Hercules

Publication date on this website: Monday, September 08, 2003
Company: Io Ltd
Category: Press Releases : Industry News (Market)

Summary:
Ruggedised control systems based on one of the world´s most popular microcontrollers are being used to refurbish the RAF C130 Hercules military transport aircraft.

Full Text:
Ruggedised control systems based on one of the world´s most popular microcontrollers are being used to refurbish the RAF C130 Hercules military transport aircraft.

Sub-contractor Io Ltd was selected by Marshall Aerospace to design three control systems based on the PICmicro, to add functionality to the plane´s audio bus. By applying commercial off the shelf (COTS) technology in this way, the developer was able to design economic upgrade modules - and then build, test and deliver the first unit starting less than five months after the contract was placed.

The modules attach to the Hercules´ existing audio intercom system, adding audio combining facilities, a keypad for data entry, plus an annunciation system that delivers prioritised voice or alert tone warnings to the crew of hazardous events. Each of the three systems is provided as a rugged line replaceable unit (LRU), in the form of a panel-mounting module.

Qualification costs were kept under tight control by opting for extended temperature range versions (-40 to +85?C) of long-lifecycle commercial components, and then designing the PCBs and modules using know-how amassed by Io from more than two decades in industrial control, and ongoing experience with COTS military projects over the last five years. Among the key principles are careful selection of chip packaging to avoid types susceptible to temperature stress – Io chose TQFP-footprint PICmicros for example - careful selection of inter-board connectors, and the application of a lot of detailed know-how related to the thickness of PCB materials, board mounting and stiffening etc to proof the modules against harsh temperature and vibration conditions. Io also tries to incorporate field programmable devices where possible for flexibility. In this instance, the use of in-place programmable PLDs for the glue logic - the boards are conformally coated so socketed components are not viable - allowed a spec change to be achieved for a total addition of just three weeks to project timescales, including the necessary qualification and certification.

The selection of a 16 Series PICmicro – a popular choice for embedded systems in consumer appliances - was driven mainly by reliability considerations. Io views the simplicity of this
microprocessor, which doesn´t force designers to use dynamic RAM, or incorporate acceleration features such as caches that might give rise to unexpected conditions - as a major advantage for systems designed for intrinsically reliable operation. In this instance, the PICmicro´s architecture simplified the audit trail for the firmware to meet the necessary RTCA/D0-178 standards.

The initial development work was followed by rigorous environmental stress screening and qualification test programs for humidity, acceleration, overpressure, altitude, explosive decompression, temperature, vibration and shock using Io´s own in-house equipment - an investment that contributes greatly to the company´s ability to deliver modified COTS systems rapidly.

"COTS-based development approaches can reduce military projects costs by an order of magnitude, along with major reductions in timescales, typically with little or no compromise in performance", notes Roger Kemp of Io Ltd. "In this instance, the only minor concession that had to be made was a relaxation in specified cold start temperature from -50 to -40?C, an inconsequential change to the headline requirements as this equipment is located in the aircraft interior".

Contact:
Roger Kemp at: Io Ltd, Woodhouse Barn, Swaffham Prior, Cambridge CB5 0HT UK. Tel: +44 (0)1638 742390; Fax: +44 (0)1638 743821; roger.kemp@ioltd.co.uk; http://www.ioltd.co.uk