Simple D-A Converter

from an idea by M Wiegers Two simple to build 4-bit digital-to-analogue converters are described here. One trans- lates a 4-bit BCD code into 10 analogue voltage levels, the other accepts a 4-bit binary code and outputs 16 voltage levels. Both circuits comprise a digital decoder with open collector outputs for control- ing a resistance ladder. The analogue voltage is obtained by controlled connection to ground of a particular section of the ladder, and buffering the drop so obtained with a tran- sistor. Table 1 Resistor values relative to 1 k52 16-step binary version Notwithstanding their relatively low resolution (10 or 16 steps), the circuit should have many possible applications, includ- ing driving digitally controlled power supplies, triangular wave and sawtooth generators, and A- Dconverters. 4- Table 1 lists the relative values D3 15 H of the resistors in the ladder network, starting from Ri =1KO. Three values are given for each resistor: the left-hand column shows the theo...