schlae/comix-35

The COMIX-35 is an improved clone of the COMX-35 1802 home computer

comix-35's Issues

Crystal oscillator circuit and U4

You are correct that a specific component is needed for U4, but a 74HC04 is not what is required for the circuit you have chosen. Your oscillator circuit is for use with unbuffered inverters (like a 74HCU04) which typically have a voltage gain in the hundreds. A buffered inverter (like a 74HC04) has a voltage gain of over 10,000. See National Semiconductor application note AN-340 which is on pdf page 76 of this data book http://bitsavers.org/components/national/_dataBooks/1983_National_74HC_Databook.pdf . A crystal-controlled oscillator should not oscillate without a crystal. If you remove the crystal from your 74HC04 oscillator it will, in my experience, oscillate at around 40 MHz or higher. With the crystal in circuit, it may oscillate at the crystal frequency, or the frequency measured without the crystal, or both at the same time. With a 74HCU04 in use it will not oscillate without a crystal. The disadvantage of the 74HCU04 is higher power supply current, which is unlikely to be an issue in your design. Using the other inverters in the 74HCU04 as inverters isn't a problem, it is a few nS faster than a 74HC04. See 74HC data book pdf page 130 for the 74HCU04 data sheet, oscillator circuit page 132. Otherwise nice re-design, not using 4000 CMOS is a good idea and your keyboard is light years ahead of the original.

BOM error?

C27 is 1uF in the BOM and the schmatics but links to 810-FG24X7R1H334KNT6 which is 0.33uF.

3D printed Case

Although it is a WIP I think it looks promising. I will upload the files once finished