UART transmitter built of digital logic IC circuits
A 555-Timer was used as clock source (9600 Hz). The clock was connected to a Johnson decade counter with 10 decoded outputs.
8 of the ouputs was connected after some combinatorics to the select input of a 8-input Multiplexer. The multiplexer was also connected to the 8-pol switch. In this way each one of the eight switches will be selected in turn and outputted by the multiplexer.
The 2 remaining output pins of the Johnson counter was used to generate the stop and start bit of the transmission.
After sending the stop bit, the clock input to the Johnson counter will be stopped (D-type Filp Flop forcing it high). When the button is pressed, the clock is freed and continues (Master clear on D-type Flip Flop).
NE555 DIP-8 Timer
74HC4017 Johnson counter
74HCU04N Hex inverter
SN74HC02N Quad 2-input NOR gate
4011B DIP-14 Quad 2-Input NAND gate
CD74HC151E 8-Input Multiplexer
SN74HC174N DIP-20 Octal D-Type Filp Flop
74HC11N DIP-14 Triple 3-Input AND gate
Tags: integrated circuits