The 74HC595 has lengthy been one among my favorite logic ICs. It takes a serial bitstream and converts it right into a parallel output with 3-state drivers. They are often cascaded virtually infinitely, permitting you to create extraordinarily large parallel output phases for driving giant LED shows or absolutely anything else that wants an on/off sign. This 8-Bit Serial DAC makes use of the 74HC595 shift register to drive an R2R resistor ladder, making a fundamental DAC (digital to analog converter) that’s not solely cheap however opens up the internals of a DAC so that you can probe with take a look at tools.

The downsides of utilizing an R2R ladder are usually decreased accuracy and better integral and differential nonlinearity. Don’t know what these are? Properly, this package is a good way to be taught! As a result of discrete resistors are by no means fairly the very same worth, you find yourself with slight variations between the perfect voltage output at any explicit worth and what’s truly output. Even in DACs which can be a part of built-in circuits, getting the resistors laser-trimmed can’t fairly take away all this nonlinearity. As an alternative, it could possibly simply be decreased to an appropriate stage for any explicit utility.

As a result of the 74HC595 is proscribed to roughly 30MHz (particular person gadgets differ, and you may take a look at a number of to seek out some that may deal with increased frequencies), an 8-Bit DAC like that is restricted to at most 3.75Msps. That is greater than ample for even very high-quality audio output, and even excessive sufficient to do some fundamental RF experimentation within the AM radio band.

The venture has been launched below the MIT license, so you possibly can research the implementation and make modifications or implement an analogous circuit your self on a breadboard! However for the worth, it’s good to have all of the elements on a PCB with a handy pin header for attaching to a microcontroller.