Appraisal of my ZX81's worthiness?

[Monty]

Auto tune is often mostly harmless but also completely useless for getting a modern TV tuned in. Where possible use manual tune and fine tune. Unfortunately some TVs will only lock on to signals that are at, or very near to one of the ‘correct’ TV channel frequencies. Because the modulator in a ZX81 is completely analogue and does not use a crystal oscillator, the frequency can be in-between the official allocated channel frequencies...

Thanks for the background info, that explains why neither of my HDTV's could lock onto the Zeddy.

Well, there’s not many test programs for a 1Kbyte machine. You can type in this to discover how much RAM your Zeddy thinks it has:

PRINT PEEK 16388+256*PEEK 16389

Result
17408 = 1k byte of RAM
18432 = 2k bytes of RAM
32768 = 16k bytes of RAM

A normal European ZX81 should report 17408.

As does mine:

Then, if you can sort out a suitable audio lead (mono 3.5mm jack plug at the ZX81 end, plug into the EAR socket), a suitable plug for your audio source at the other end (a stereo 3.5mm jack plug {see note} if your audio source is stereo for example), you can load some of dr beep’s 1K games to play

Notes: modern audio devices are nearly always two channel stereo. But the ZX81 is mono. Any leads or adaptors should only use one of the stereo audio channels (by convention the left channel). If the leads or adaptor just connects the left and right channels together, this often messes up the signal (and the ZX81 won’t load anything) and in some cases may damage your audio device. A cable like this is what you want (3.5mm STEREO Jack Plug to 2 x MONO Jack Plugs SPLITTER Converter Cable Lead 1m).

Noted! I've ordered that very item from eBay.

The ZX81 was designed for use with shoebox mono cassette tape decks, which can output a loud signal with a relatively large amplitude. With the vast majority of modern audio devices, a lack of signal amplitude will result in the ZX81 acting as if it is completely deaf. So you may need to use an audio power amplifier. You need one with a headphone output. Cheap mains powered PC speakers are often okay for this. Or if you can wait for a cheap module from China, a LM386 audio amplifier from eBay (e.g, like this one).

Mark

That's an option that I'll keep in mind. Thanks.

If you are just looking to load games reliably and fairly cheaply try one of these:

https://www.ebay.co.uk/itm/254080943285

Doubtless there are others but I have bought a number of these (and bundled them with refurbished zeddies) and found them to work well and the seller is very helpful.

It is no faster than tape but very reliable and you can download and run ‘most’ games on it.

This could be a nice and cheap stop-gap till I can get hold of a ZXpand. It can also work with other machines, which is a great bonus.

I haven’t quite figured out how multi-part loading games work on it yet but these are rare-ish.

Multi-loading games exist for the ZX81? I'd like to know more about this.

Hi Monty.

The composite mod is a must I feel, as is the Zxpand+ which is more than just a storage/memory device.

Hi Moggy, yes the composite mod is something that I'd like to tackle so that I'm not restricted to using my older TVs and RF. It's been years since I've done any soldering work so I'm slightly fearful of screwing it up and damaging the machine.

Things I have done with my ZXpand+ include AY composition done with a tracker program and software for playing AY (3 channel built in) add on daughter board for 6 Channel, GM MIDI file player,PC text sent via serial/usb connection to to ZXpand+ with a connected speech box(Cheetah) for a speech program without having to type allophones manually.

Is the Cheetah speech unit for ZX Spectrum compatible with the ZX81 via the ZXpand+?

Also the ability to save/load to and from memory blocks make it a very useful device I find.

My question is, where do you purchase the ZXpand from? All I can find on SellMyRetro are the cases and there's no details of where you can place an order for the expansion unit.

That's a very nice tv picture for the RF-signal. It looks as nice as composite signal.

Thanks, the photos really don't do it justice: the display is actually much brighter than is depicted by my images.

It's always a nice surprise to gain good results with RF!



When I typed LOAD "" the RF signal appeared to lose all cohesion on my 4:3 LCD PAL TV - as can be seen here:



I've seen the issue discussed here https://sinclairzxworld.com/viewtopic.p ... 0&start=10. Does this mean that the ZX81 will only display 100% correctly on a CRT TV? I do have one from 2000 with SCART and A/V terminals if needs be. Also, regarding the composite mod - will it be a matter of trial and error to see if I encounter the back porch problem or is there a way this can be ascertained beforehand?

Thanks for all your help for a newcomer!

[1024MAK]

Hi Monty.

The composite mod is a must I feel, as is the Zxpand+ which is more than just a storage/memory device.

Hi Moggy, yes the composite mod is something that I'd like to tackle so that I'm not restricted to using my older TVs and RF. It's been years since I've done any soldering work so I'm slightly fearful of screwing it up and damaging the machine.

If you wait for approximately 24 to 48 hours, a shop that sells prebuilt modules (you just need to solder four or five wires) that produce a nice clean composite video output is about to reopen. I’ll post a link when it reopens to the item I am talking about...

My question is, where do you purchase the ZXpand from?

Alas the person that makes them currently does not have any for sale So you will have to be patient and wait in the hope that he will build some more. Keep watching the sales section of the forum and keep checking Sell My Retro...

When I typed LOAD "" the RF signal appeared to lose all cohesion on my 4:3 LCD PAL TV.

I've seen the issue discussed here https://sinclairzxworld.com/viewtopic.p ... 0&start=10. Does this mean that the ZX81 will only display 100% correctly on a CRT TV? I do have one from 2000 with SCART and A/V terminals if needs be. Also, regarding the composite mod - will it be a matter of trial and error to see if I encounter the back porch problem or is there a way this can be ascertained beforehand?

To keep costs low, the ZX81 and TS1000 cheat with the tape out signal. They use the TV video signal to do both. Hence yes you will loose the normal video picture. This happens with both CRT and LCD TVs.

We can tell if your Zeddy should generate a back porch if you can tell us the ULA version (the number printed on the top of the chip). If you have a ULA that does generate the back porch part of the video signal, then that should be okay. If you have one of the two earlier ULA versions, then it’s a case of try it and see... Some TVs don’t care, others don’t display picture with any real contrast. But your RF picture is really good, so as the video content of the RF output is derived from the ULA, and a composite modification will use the same signal from the ULA, I don’t think you will have a problem.

Mark

[1024MAK]

BTW, this was the last (most recent) listing for ZXpand+ systems...

They sell out faster than hot cakes...

Mark

[Moggy]

There are some add ons that will fit will work with the zeddy and the spectrum,for,example I have an EPROM burner that can be used with both and not forgetting the ZX printer or Alphacom printer that natively work with both computers.
However I suspect the Cheetah sweet talker for the spectrum will not work on the zeddy as it possess two extra "pins" call them what you will on its expansion connector (see pics) but it's better someone more qualified should answer that.

[mrtinb]

If you need a storage solution, and cannot wait for the next batch of ZXpand+s, there's a new cheap storage solution on the German forum.

It's the ZX-Wespi. You just buy an ESP32, and connect 4 wires to your ZX81 PCB. (Plus a tantalum capacitor, and three resistors.) It's a very simple circuit you can make on a perfboard.

When you type the command LOAD"", the ZX-Wespi detects this, and displays a menu with all software stored in it's internal flash. The software can then be loaded with a keypress. It's quite fast, as the menu has a buitin fastloader. Software is loaded in seconds.

Software is added via a webbrowser connected to the Wespi's builtin server.

[1024MAK]

...composite mod is something that I'd like to tackle...

Hi Monty.

The composite mod is a must I feel, as is the Zxpand+ which is more than just a storage/memory device.

Hi Moggy, yes the composite mod is something that I'd like to tackle so that I'm not restricted to using my older TVs and RF. It's been years since I've done any soldering work so I'm slightly fearful of screwing it up and damaging the machine.

If you wait for approximately 24 to 48 hours, a shop that sells prebuilt modules (you just need to solder four or five wires) that produce a nice clean composite video output is about to reopen. I’ll post a link when it reopens to the item I am talking about...

And here is the link to the item that I strongly recommend you buy so that conversion to composite video is as easy as possible

Buy soon, as these sell fast...

Mark

[Moggy]

For God's sake don't tell Lardo he, orders them by the pallet load!

[Lardo Boffin]

Lardo has already seen them!

And I only ordered 10. Thats a really small pallet.

[1024MAK]

Me rushes off to see how many are remaining...!

Mark

[Monty]

BTW, this was the last (most recent) listing for ZXpand+ systems...

They sell out faster than hot cakes...

Mark

Thanks for the heads up. I've requested that I be notified when he has new stock.

If you need a storage solution, and cannot wait for the next batch of ZXpand+s, there's a new cheap storage solution on the German forum.

It's the ZX-Wespi. You just buy an ESP32, and connect 4 wires to your ZX81 PCB. (Plus a tantalum capacitor, and three resistors.) It's a very simple circuit you can make on a perfboard.

When you type the command LOAD"", the ZX-Wespi detects this, and displays a menu with all software stored in it's internal flash. The software can then be loaded with a keypress. It's quite fast, as the menu has a buitin fastloader. Software is loaded in seconds.

Software is added via a webbrowser connected to the Wespi's builtin server.

That looks pretty neat! I appreciate these recommendations - I certainly have a number of options to choose from.

And here is the link to the item that I strongly recommend you buy so that conversion to composite video is as easy as possible

Buy soon, as these sell fast...

Mark

As you soon as you posted the URL, I heeded your words and immediately made a purchase.

Thanks again for all the help everyone. I anticipate that I'll be having a lot of fun this autumn/winter.