Sinclair ZX80 / ZX81 / Z88 Forums

Here's a good one.

I'm preparing a zeddy to go into a wooden case, which requires me to extend the ports, etc. to the side of the case.

However, in the case of the SD card, I'm having a minor puzzle.

The longer of the two extenders works, the shorter one comes up with 9/0 all the time. Tried various cards of different speeds and capacities... no joy. I've compared the pin outs and connectivity of the two, and they appear exactly the same.

I just can't work out why the shorter one isn't working... I should have thought it would be the other way around, if anything. If I can solve this, it would mean less cable in the case, but I thought I'd ask for thoughts and opinions before I start cutting and soldering.

Whilst I know zilch about these things I do know that the spand card slot is one that doesn't detect whether the write protect tab is set on the card and will write to it regardless of position so does it require an extension cable/slot that obeys the same rule?


Again forgive my stupidity

Good point/question ... I haven't got a clue.

The write protect thing is something I was aware of and had checked, and they work with a PC ok.

Have you measured and compared the capacitances of the lines agains Ground? Especially the one of the 3.3V?

I found this and thought it might shed some light on your problem.

https://forum.prusa3d.com/forum/origina ... -extender/

Thanks - I'll give all that a check.

Paul - How do I check the capacitance please? Did you mean resistance? Do I really want the multimeter using capacitance tests by putting voltage into the card?

Apologies for my newbieness.

It does seem that there is a resistor installed on the one that doesn't work, against the one that does. I'm going to try removing that in a day or two, and see what happens.

Stuff it. I couldn't resist. No, removing the resistor didn't solve it.

No, please test capacitance without card installed and without inserted in zxpand

My multimeter measures it (own setting)
My guess would be that wire capacitance of the short lead disturbes the signal line
OR
That an additional 10-100uF capacitor between 3.3V and ground will help against too thin wires for voltage transportation.