Sinclair ZX80 / ZX81 / Z88 Forums

Seems by chance that also specdrum was using A5!

The ZN428 is a Ferranti semiconductors product, and is quite old, so certainly existed in the 1980s. See the dates at the end of this data sheet . Of course, it would not have been cheap… Then we can design two absolutely compatible boards to choose from! :) Is bus signal A5 good to go (meaning the...

@Freya : is ZN428 is a nice chip, but is "era compatible"? Seems to me that is a product of the 90s more than the 80s... With the solution of MAK you should add really just a bunch of resistors and you can go with a single widespread 74hct377! More, with a simple DPDT switch in the middle of the R2R...

Oh, I think it’s possible to get even simpler if you don’t mind doing it the “dirty” way… :lol: A5 to /E (pin 1) on the 74xx377 /IORQ to CP (clock pulse)(pin 11) on the 74xx377 No other chips, diodes, or resistors (for the control lines) needed. Just ensure that the software does not try to input (...

Yes, this is what I was thinking about! Very nice music, and as usual Yerzmyey is an artist! 4 bits doesn't seem bad, one 377 may suffice even for the two stereo channels in case! The tracker can even be ported if there are the sources or there is the author around. In the meantime I had a new idea ...

Here a very nice video on how to build the perfect keyboard for the ZX81! It will be better than anything else you have and you'll start to write on ZX81 and then copy the text to the PC LOL ;) https://www.youtube.com/watch?v=c1G5rX_YvCA PS: this is the third part of a video building the entire syst...

@MAK Sorry, I didn't see your answer on the second page until I submitted this reply! Regarding circuit with nowdays prices with 0.10$ you can buy a microcontroller more powerful than the full ZX81 with high quality audio interface already onboard! (e.g. https://www.cnx-software.com/2022/10/22/10-ce...

@Moggy Circuit is very simple: there is an octal flip flop (74377) that drive the resistor DAC network. Two of them can output stereo sounds. The diodes are to enable the write on the flip flops on proper address, e.g. $BF (0b11011111) for the A5 address line (A0 and A1 are reserved for NMI and keyb...

I gave my 5 points to sokob and f1 pitstop

Without the full *pand interfaces I suspect that a single 74273 or 74377 might be used to drive the resistor DAC network. For the HW experts, something like the following picture can work? photo1676223675.jpeg Notes: - the picture is just to give an idea of the realization, and should be revised and...