Introduction: 

Do you like listening to music? A long time ago, the gramophone was a great invention that brought much pleasure to people. The sound signal was recorded in the mechanical grooves on a medium, which is known as analog-recording. Those days are long gone, as we now live in a digital world, where everything is recorded as numbers. This gives rise to the term that we all are familiar with, digital music. Actually, we now have digital everything or "all-things-digital". Movies in theaters with the old 70-mm celluloid film format are like the old gramophone. We all are watching digital videos as well. In fact, the most frequently used instrument when you do lab work is the digital multimeter, which converts analog signals into numbers. But if we store music as numbers in the digital world, how do we listen to it? After all, music or sound is air pressure wave in the analog physical world. We need a way to convert our digital sound and sight recordings into physical analog signals. This is known as digital-analog conversion (DAC), the reverse of analog-digital conversion. You will research and design a circuit to do 8-bit DAC.

Discussion and suggestion: The first answer is: "No, you can't buy a ready made chip to do the job." You will have to design and build one, and of course, you are expected to go through tried-and-true designs, of which one of the best known is R-2R ladder circuit. Below is an illustration how it works.
 


Here is an APP that helps you analyze the data:
(if you have problem, contact the instructor for help - the APP is designed with the assumption that the measurement fluctuation is roughly the same as the DMM precision. If the error is much larger, it may indicate something wrong. Note that this analysis should help to illustrate the concept of error due to the errors of the resistors which is different from the concept of error due to the precision of the instrument).






Components: you will need:

- 9 resistors of value 2R, e. g. between 2 - 5 kOhm - 7 resistors of value R, e. g. between 1 - 2.5 kOhm. (you can use smaller or larger values resistors, as long as they are of high accuracy and precision).
- for visual effects, 8 LEDs so that you know which bit is on and which bit is off.
- 8-bit dip switch so that you can manually flip each bit on or off.
- If you use dip switch or SPDT, an octal buffer driver chip with high input impedance (e. g. 100 kOhm to 1 MOhm or greater) to power the LED's, such as 74LS244
- some cool idea (costs a bit more): each node can be monitored with a 10-bar color LED indicator so that you can actually see the voltage goes up and down as you change the input bits. These bars are reusable for all other lab projects whenever you just want to monitor some voltage.

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