Logic gates are the building blocks of digital electronics. Simple logic gates are efficiently implemented in various IC packages such as the 74HCXX series. However, it is educational to have a look at the implementation using just NPN transistors. ...
The 74HC165 and 74HC495 are useful integrated circuits for dealing with multiple digital inputs and outputs. In a recent project, I used the following prototype based on a variant of the above simple circuit schema: The four 74HC495 ICs gives access to 2 x 16 bits accessible through IDC connectors controllable using just three pins on the microcontroller (DATA, CLOCK, LATCH). Similarly, two 74HC165 ICs gives access to 16 input bits through another IDC connector. ...
The 74HC595: an 8-bit serial-in/serial or parallel-out shift register with a storage register and 3-state outputs. If higher load is required there is also the TPIC6C595 (e.g., for driving LEDs), or it should be paired with for example ULN2803 (as used in this 16 bit gate) or similar. For multiple inputs see the 74HC165. Figure 1: Pin-out 74HC595. The basic usage is to serially transfer a byte from a microcontroller to the IC. When latched the byte will then in parallel be available on output pins QA-QH (Q0-Q7). ...
The 74HC165 is an 8-bit parallel-load or serial-in shift register. Figure 1: Pin-out 74HC165. Wiring: Pin 8 (GND): GND Pin 16 (VCC): Voltage 5V Pin 11-14 & 3-6 (A-H): Input 1-8 Pin 1 (SH/LD): shift/load pin Pin 2 (CLK): Clock pin Pin 9 (QH): Data output pin Pin 15 (CLK INH): Clock-inhibit pin (or GND) Clocking is accomplished by a low-to-high transition of the clock (CLK) input while SH/LD is held high and CLK INH is held low. CLK INH can be wired to GND to save a pin on the microcontroller. Unused inputs pins should be grounded as well. Multiple 74HC165 ICs can be daisy chained by wiring the serial-out pin 9 (QH) to pin 10 (SER) of the succeeding IC allowing us to tie multiple 74165 ICs together that can be controlled using only 3 pins. ...