Funny chat on two ZX81 16k.

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XavSnap
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Funny chat on two ZX81 16k.

Post by XavSnap »

Hi,
If you have two ZX81, you can experiment a funny setup.

Take two computer, link the EAR to the MIC and the MIC to the EAR.
Launch this "P" file on both computers.
Set the first as "Master", the second one as a "Slave".
Take an very cleaver friend on the second ZX81...
And ... it's done... Your ZX81 is a "AI CHAT-ZX R1" computer !

:shock:

This code is issus from the "Graphics toolbox"
But can be diet to fit in a ZX81 1k...
ZXCHAT.P
(2.03 KiB) Downloaded 5 times
Have Fun !
Xavier ...on the Facebook groupe : "Zx81 France"(fr)
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XavSnap
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Re: Funny chat on two ZX81 16k.

Post by XavSnap »

I will be curious to know if a Skype session can "talking" to another ZX81... if you have only one computer.

:ugeek:
Xavier ...on the Facebook groupe : "Zx81 France"(fr)
Moggy
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Re: Funny chat on two ZX81 16k.

Post by Moggy »

I've tried linking ZX81s this way in the past, probably one of the first things I ever did outside of the norm, and it doesn't work as the signal the MIC port puts out is not strong enough without amplification to be read by the second ZX81s EAR port.
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1024MAK
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Re: Funny chat on two ZX81 16k.

Post by 1024MAK »

I was wandering about how the two Zeddies were being linked.

The attenuation of the signal in the circuit for the mic socket is substantial, hence the resulting signal is a very low voltage (weak).

Meanwhile the ear input needs a relatively high voltage for the ULA to detect it, meaning it needs a strong signal.

As Moggy says, an amplifier is therefore needed.

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XavSnap
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Re: Funny chat on two ZX81 16k.

Post by XavSnap »

Ok, in this case, two mono amplifier are need.
One per EAR sound output.

Yes, in this case, the amplifier is a tape recorder (REC+PAUSE keys): (pdf-FR)
Reliez_2_Zx81_MicroSystemes29.pdf
(8.37 MiB) Downloaded 12 times


EDIT:
Or place two mono amplifiers: (2x1$=2$)
Capture d’écran_13-6-2024_63912_www.aliexpress.us.jpeg
Capture d’écran_13-6-2024_63912_www.aliexpress.us.jpeg (18.65 KiB) Viewed 39 times
https://www.aliexpress.us/item/3256806185357515.html

3.5mm mono cable to cut and connect to the terminals (1x1$)
https://www.aliexpress.us/item/3256804866242048.html

A 3 to 12v DC power supply (1$)
https://www.aliexpress.us/item/3256805002430910.htm
Xavier ...on the Facebook groupe : "Zx81 France"(fr)
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XavSnap
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Re: Funny chat on two ZX81 16k.

Post by XavSnap »

The wiring diagram:
ZxLink.pdf
(19.28 KiB) Downloaded 3 times
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Moggy
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Re: Funny chat on two ZX81 16k.

Post by Moggy »

I don't think this will actually work, Xavier.

The amplifier unit you have pictured is a simple LM386 POWER op-amp and whilst it may just have the grunt to power a signal into the Zeddy it requires pre-amplification at the input usually at a domestic line level of about 2-300 millivolts and rest assured the output from the Zeddie's MIC socket is nowhere near that and would, I suspect, require more than one pre-amp stage.

Just as an example I have built a small device to make the Spectrum's output a bit louder than the beeper and the device I used is a type of power amp that requires no pre-amplification and has a sensitivity of about 40 millivolts. This works wonderfully with the Spectrum but when used with the Zeddie's MIC socket the signal is so weak it doesn't even register.


In short the LM386 is just not sensitive enough at its input and electronically speaking is a bit of a noisy beast even fitted with what I suspect are components for a simple Zobel network which may or may not help to tame any high frequencies/spikes, so would require either battery power or a very well smoothed and regulated power pack.

I don't know if the power pack in your link is suitable as all I get is a blank page when I try to open it but anything priced at $1 is unlikely to be any use.
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