Inexpensive AD/DA converter
Ferranti's ZN426-8 is an 8-bit monolithic digital to analogue converter containing an R/2R ladder network with precision bipolar switches and a 2.5 V precision voltage reference. The circuit shown here is connected to the PC's parallel printer port, and provides a simple means of communication with the analogue world. It is capable of generating as well as reading voltages between 0 and 2.55 V in steps of 10 mV. The ZN428 also as an A-D converter with the help of a comparator. The circuit is powered by an external 5-V source, and controlled by a small Pascal Program.