IMPROVED LIGHT PEN
AMONG hardware releases promised by dK'tronics is a new version of its Spectrum light pen. The pen is supplied with software for both 16K and 48K versions and is a vast improvement on the old version.
As with the majority of light pens, there is an interface which connects to the computer, in this case the inevitable black box which fits into the user port and which is dead-ended, and a pen which plugs into the top.
The interface contains a minimum of electronics; all the work is performed by the software. A TV picture is made up by a spot of light which zig-zags down the screen. By timing how long it takes from the start of the scan to when it is picked up by the pen, the software can determine the position.
The instructions show how you can use it in your programs to choose from a menu and give you the address of the 96 bytes of code needed. In addition, the software contains a drawing program which can be used to create pictures.
The program offers a number of options to draw lines, arcs, boxes and circles, fill areas, change colours, insert text and LOAD and SAVE pictures to tape. On a 48K machine up to four screens can be kept in memory at once and then recalled, singly or one after another, to provide limited animation. The acid test of a light pen is when trying to draw freehand and that it does remarkably well. The straight lines are straight and the pen draws where it is pointing.
The only disadvantage is the lack of error-checking on some of the commands, such as when drawing an arc which goes off the screen when you are dumped back into Basic. You can return to the picture without losing it but it is annoying.
If you are looking for an accurate light pen you could do far worse than this pen which sells for £19.95, from dK'tronics Ltd, Unit 6, Shire Hill Industrial Estate, Saffron Walden, Essex CB11 3AQ and computer shops.