Sinclair ZX80 / ZX81 / Z88 Forums

Almost certainly Resistor Network! Ah! I found this component https://cdn.sparkfun.com//assets/parts/5/8/6/8/10855-01b.jpg /Martin Just to double-check, it would be this type: https://protostack.com.au/wp-content/uploads/newproducts_jan14_05.jpg where the common connects to +5V so as to pull all th...

Aaah, yes. I see now. I tried tapping into the keys directly before but got EMI problems due to the long wires. So I'll need a buffer. Also, I'd like to keep my board neat so a plugin unit seems more elegant. I understand now, C0 - C4 is the columns. Thank you for the suggestions.

In the schematic is 5,6,7,8 and 0 in R3 and R4?

Also, what does C0, C1, C2, C3 and C4 refer to on the keyboard matrix?

Found it!

viewtopic.php?t=2910

Perhaps I'll do something like THIS instead:

https://www.sinclairzxworld.com/viewtopic.php?t=1793

It would be far more useful for the game controller to map to the keys but in a neat way.

Can someone suggest a program to verify a Kempston Joystick is working? I saw the code somewhere, but now I cannot find it again. It used the assembler commands to check the value of a register as you press buttons.

Hi, I did Google it, but for the life of me, I cannot find what I'm looking for. I remember seeing somewhere an adapter for upgrading the RAM of a ZX80 on the mainboard itself. It plugs into the 2114 RAM slots. I have my ZX80 replica and it is experiencing RAM pack wobble issues. I cleaned the conta...

I'm looking for a ZX81 motherboard/main board. I have a spare ULA and ROM if it needs.

Yes, monochrome.

Yeah, I was actually looking at the optocoupler specs with just that in mind. I was wondering about using a capacitor instead. From what I see on the web though about video driving techniques, the series capacitor used is rather large. https://www.maximintegrated.com/en/images/appnotes/3768/3768Fig0...

To protect my ZX80 I'm thinking of introducing an optocoupler into the video signal path. I can then use the output of the optocoupler and feed into the back porch generator. I'll then give the back porch generator its' own DC supply. I just have to make sure of the input impedance the ZX80 sees.