DIY Pocket Op-Amp Lab Kit Built Without Op-Amps!
Op-amps built into AVR DB microcontrollers make this pocket-sized project possible.
Some engineers consider operational amplifiers, or op-amps, to be the coolest building block for circuits and for good reason. They are easy-to-use and very versatile. Learning to use them just became significantly more accessible with David Johnson-Davies' Pocket Op-Amp Lab.
"This is a self-contained tool to allow you to experiment with the configurable op amps provided in the new AVR DB-series processors from Microchip. It shows the configuration as a circuit diagram on the display, and lets you reconfigure it by selecting options from on-screen menus."
Built entirely on a breadboard, the Pocket Op-Amp Lab consists of a 240x135 color TFT screen, a couple of pushbuttons for input, passive components and a Microchip AVR128DB28 microcontroller. That chip is the key to the project.
In late 2020, Microchip announced a new series of AVR-based microcontrollers. The 8-bit core has a familiar-sounding feature set: 128 KB of Flash, 16 KB of SRAM, clock speed up to 24 MHz, and a (breadboard friendly) SPDIP package.
The exciting difference is that Microchip combined the popular 8-bit core with analog capabilities. In addition to the commonplace analog-to-digital (ADC) and digital-to-analog (DAC), the AVR DB contains three software-configurable operational amplifiers!
Software registers can configure these op-amps just like you could build them on a breadboard. The chip has eight different wiper positions on a resistor ladder, providing ratios: 1/15, 1/7, 1/3, 1, 5/3, 3, 7, and 15. Multiplexers allow the resistors, inputs, and outputs to be connected in a variety of configurations.
Pocket Op-Amp Lab's LCD shows a graphical representation of the op-amps' configurations. Using the simple pushbutton interface, a user can set up a voltage follower (buffer), non-inverting amp, inverting amp, difference amp, and can even cascade the two stages.
With the cascade, the design achieves gains up to 225!
While op-amps have always been an approachable IC, we see Pocket Op-Amp Lab serving two purposes. First, as an educational tool for op-amps. And second, as an evaluation tool to see if the AVR DB's amplifiers are useful in your application.
Johnson-Davies used the AVR128DB28 in another project we covered, a LED Logic Lock.
For more information, head over to the Pocket Op-Amp Lab write-up on Technoblogy. Johnson-Davies has a detailed explanation of the firmware's operation and a link to the code.