The 74HC595 has lengthy been certainly one of 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 nearly infinitely, permitting you to create extraordinarily broad parallel output levels 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 primary 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 gear.
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 an effective way to study! 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 really output. Even in DACs which are a part of built-in circuits, getting the resistors laser-trimmed can’t fairly take away all this nonlinearity. As an alternative, it will probably simply be lowered to an appropriate degree for any explicit software.
As a result of the 74HC595 is proscribed to roughly 30MHz (particular person gadgets differ, and you’ll take a look at just a few to seek out some that may deal with greater 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 primary RF experimentation within the AM radio band.
The mission has been launched beneath the MIT license, so you’ll be able to examine 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 parts on a PCB with a handy pin header for attaching to a microcontroller.
