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R/2R ladder DAC

This is a famous digital to analog converter that uses a resistor ladder network. It has 8bit resolution but you van easily increase it if you follow the pattern. The circuit is very simple and doesn't require a lot of time for you to build. It combines both simplicity and fidelity.

Notes

The DAC has 8bit resolution, which means will convert any digital information with the length of one byte.
Normally, R/2R ladder network has no bandwidth limitations. However, bandwidth is limited due to the necessary output buffer. This reduces the speed of the DAC.
Accessory bandwidth limitation is coming from the low slew rate of the OPAMP, because we are dealing with a large signals. In the circuit presented here I used LM358.
Components

  • Nine 20K resistors (1/4 Watt).
  • Eight 10K resistors (1/4 Watt).
  • One LM358 OPAMP.
  • A 8 pin DIP socket (for the LM358 chip).
  • Female pin headers for the digital inputs, the output and the power supply.
  • A small piece of a Veroboard.
  • Wire for connections.
  • Solder and soldering iron.

Also you will need a stabilized 5 Volt external power supply (or even 3.3Volts). It's better to use higher volts (e.g. 6 Volts or a 9 Volt battery) to avoid saturation effects.

Schematic Diagram

Here is the schematic diagram of the R/2R ladder DAC (click on the picture to enlarge).

Attention: Vin is the power supply. It's better to be higher than 5 Volts (e.g. 9 Volts from a battery), in order to avoid saturation effects. I chose the LM358 OPAMP because it can behave quite well close to zero (meaning there is now saturation with an input close to zero volts). However, you can use whatever OPAMP you want, in order to achieve the desirable performance.

 
Pictures

In the following picture you see the circuit already build on a small piece of a Veroboard. It is designed to fit perfectly to Basic Stamp's 2 programming board or AVR board of Education.

Created: 18/11/2005
Updated: -

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