Multitasking Pins: Clever Circuit Design with 5V

Circuit diagram:

Description

It is quite reasonable that smaller, more affordable microcontrollers possess a reduced number of connection points compared to their larger counterparts – occasionally, this reduction is excessive. The designer has thoughtfully considered methods for minimizing pin count, cleverly utilizing each connection to perform multiple functions. A potential advantage can be derived from the high-impedance characteristic of a tri-state output. This feature could be leveraged, for instance, as a chip select signal for two integrated circuits, or alternatively as a read/write signal. To achieve this, it is necessary to employ two operational amplifiers or comparators powered by a single supply voltage of 5 V, with outputs capable of reaching both full Low and Full High levels during operation (ideally, types with rail-to-rail outputs should be used).

Operational Amplifiers

Operational amplifiers (op-amps) are versatile integrated circuits designed to amplify weak electrical signals. They are commonly used in a wide range of applications, including audio amplification, instrumentation, and control systems. These devices are characterized by their high gain and ability to provide precise amplification. The LM393 and LM311 are popular op-amps, known for their accuracy and stability, and are suitable for this circuit’s design.

Suitable examples to utilize are the LM393 or LM311. The resistors within the voltage dividers in this circuit are consistently 10k. Consequently, input A resides at one-half of the operating voltage (2.5V), assuming nothing is connected to the microcontroller pin linked is at high impedance. The non-inverting input of IC1A is positioned at two-thirds of the operating voltage, while the inverting input of IC1B sits at one-third of the operating voltage, ensuring that in both scenarios, the outputs are set to the High state. When the microcontroller pin at input A shifts to Low, the output of IC1B transitions to Low, and the output of IC1A becomes High. Conversely, when A is High, the entire circuit operates in reverse.