A visual basic custom control for interfacing with GPS receivers

Because of its features, "Visual Basic" is avery adequate language for deve loping computer programs for several applications, such as Precision Agricu lture. It is easily learned; it reduces development time, making project mo difications easier; and it allows to write programs with a powerful user in terface, supporting most of the features provided by the "Windows" environm ent, such as frames, command buttons, picture boxes, dialog boxes, etc. These features, called "controls", are supported by the standard "Visual Ba sic" interpreter. They appear in a "tool box" on screen, and can be freely selected and used by the programmer. On the other hand, the programmer can create other controls, for his own us e, called "custom controls". In this case, he has to write some code, in "C ", and create a "VBX" file, to be added to his project. This paper presents a customized control for computer programs written in V isual Basic that communicate with GPS (Global Positioning System) receivers . A GPS receiver is an electronic instrument that receives signals sent by artificial satellites and, based on these signals, calculates its current p osition. It is largely used in Precision Agriculture applications, for mapp ing (soil, crops, weeds, yield) and navigating (planters, fertilizers, spra yers, harvesters). In many applications, it is connected to a vehicle on-bo ard computer, usually through a serial link, sending messages according to the "NMEA-0183" protocol. The "VBX" control presented here, a GPS receiver interface, can be included in any "Visual Basic" application. Through the computer serial port, it re ceives the most common messages sent by GPS receivers, recognizes them, ana lyses them, and collects the information they contain, such as position, ti me, data quality, number of satellites in view, etc., passing them to the a pplication. The GPS receiver interface control is currently being used by the program o f a Planter Monitor, and other applications for Precision Agriculture are e xpected to make use of it.