parallel-serial keyboard converter

parallel-serial keyboard converter As we have already said in the article on constructing the ASCII keyboard, there is another option for the computer hobbyist who wants more. This option allows serial ASCII in both RS 232C and TTL form. Provision for this has already been made on the printed circuit for the keyboard. The frequency (read: baudrate) is determined by the circuitry surrounding IC7. The fre- quency is set with potentiometer P1; it can be checked with a digital frequency meter connected to pin 3 of the 555. If desired, the range (at present up to about 400 Hz) can be changed by making C5 smaller. Because the baudrate is equal to the number of bits per second (thus making the baudrate directly proportional to frequency) this adjustment is a very simple task. The (clock-) output of the timer is also connected to the clock-input of flipflop 2. The latter receives the bits from IC6 to its data input. The serial signal appears at pin 5 of this flipflop, and the output is Fi...