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
The DAC has 8bit resolution, which means will convert
any digital information with the length of one byte.
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.
- Nine 20KÙ resistors (1/4 Watt).
- Eight 10KÙ 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
- 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.
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.
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.