Holy cow ! You are definitely brave to do this entirely in discrete logic. The last time I did a discrete logic design was more than 10 years ago for my first nixie clock. Since then, everything uses an FPGA, RasPi CPU, or both. BTW, my first major electronics project was in 1979 when I built an ASCII video terminal for remote timeshare access (110 baud dialup), and it was the same Radio Shack keyboard.
Thanks! Just swapped out several of the old 7400 style ICs in that RatShack keyboard. Installed a variety of CMOS ones such as HC, C, HCT, and had to settle for a few LS ones in sockets where none of the CMOS ones seem to operate correctly. But now have total keyboard current down to 90 mA, where as originally it sucked up 450 mA!
Holy cow ! You are definitely brave to do this entirely in discrete logic. The last time I did a discrete logic design was more than 10 years ago for my first nixie clock. Since then, everything uses an FPGA, RasPi CPU, or both.
BTW, my first major electronics project was in 1979 when I built an ASCII video terminal for remote timeshare access (110 baud dialup), and it was the same Radio Shack keyboard.
Thanks! Just swapped out several of the old 7400 style ICs in that RatShack keyboard. Installed a variety of CMOS ones such as HC, C, HCT, and had to settle for a few LS
ones in sockets where none of the CMOS ones seem to operate correctly. But now have total keyboard current down to 90 mA, where as originally it sucked up 450 mA!