Purpose of this Save/Loading device?

Discussions about Sinclair ZX80 and ZX81 Hardware
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Erm
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Purpose of this Save/Loading device?

Post by Erm »

Hello, I got this homemade device with a selection of ZX81 bits and pieces a couple of months ago. It's clearly designed to go between the ZX81 and the cassette recorder.

I'd be interested to know more about what it may actually do though, from those that understand these things! It appears to require 5v DC and has fairly obvious on/off switches and one for load/save(ing), but it also has a switch for CR or TB and I'm not sure what that does (It's in German so perhaps TB is Tonband and CR for Cassette Recorder... I'm not quite sure what the difference could be there. The input side is also labelled CR-TB).

Is it some kind of amplifier? Does it reduce noise? Obviously it must somehow improve ZX81 saving and loading from tape. I haven't tried it out yet.

The slightly obscured chip is a CD40106BE (CMOS invertor, says google).
20191116_180618.jpg
20191116_180555.jpg
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
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1024MAK
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Re: Purpose of this Save/Loading device?

Post by 1024MAK »

CMOS CD40106BE chips can be persuaded to operate as cheap amplifiers. It looks like there is also two transistors on the board. The board looks like a homemade PCB.

The switch next to the red LED looks like the power on/off switch.

Any chance of reporting the type number of the transistors and posting a photo of the track side of the board?

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Erm
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Re: Purpose of this Save/Loading device?

Post by Erm »

Yes of course. I would have removed it all, but it looks like I'll have to remove the switches and 5v socket to get the board out. The CR-TB switch just choses between 2 different resistors and neither position seems to make contact so I'll take everything out and clean it all up.
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
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Erm
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Re: Purpose of this Save/Loading device?

Post by Erm »

Here we are. Back is marked with the transistor positions (both are BC239C) and C for capacitor, R for resistor.

Any idea why the circuit is broken where those two wires come out next to that resistor at the bottom?
homemade amp2.jpg
homemade amp1.jpg
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
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XavSnap
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Re: Purpose of this Save/Loading device?

Post by XavSnap »

Hi,
May be a signal cleaner… based on the CMOS Hex Schmitt-Trigger Inverters.

:?:
SignalClean.jpg
Wiring diagram:
Wdiag.jpg
Last edited by XavSnap on Sun Nov 17, 2019 10:37 pm, edited 1 time in total.
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Erm
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Re: Purpose of this Save/Loading device?

Post by Erm »

Excellent, it certainly looks exactly like that (without checking each connection yet). I'll feed it with 5v and a cassette and see if it makes any difference.
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
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XavSnap
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Re: Purpose of this Save/Loading device?

Post by XavSnap »

pcb.JPG

Updated Kicad file:
SignalClean.zip
(491.51 KiB) Downloaded 123 times
[EDIT : Something's wrong with the Darlington wiring ? the equivalent transistor seen to had the wrong datas…

Resistors colors decoder:
https://www.mouser.com/technical-resour ... gISSfD_BwE
R1=10k
R2=? (hidden)
R3=1k
R4=100
R5=12 (!)
R6=1M
C1=? (not pol. mylar?)
C2=? (disc)
C3=? (pol.)
Values/locations not checked...
]
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avrovulcan
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Re: Purpose of this Save/Loading device?

Post by avrovulcan »

Thanks for taking the trouble to produce a circuit layout
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Erm
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Re: Purpose of this Save/Loading device?

Post by Erm »

I thought that you'd found details of a very similar device online somewhere, not that you'd created the circuit details! I'll open it up again and will let you know about the resistor and cap values.
I'm Chris, a Brit in Germany (Chr$ on the QL forum). https:\\QXL.WIN < QL related collection.
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XavSnap
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Re: Purpose of this Save/Loading device?

Post by XavSnap »

Thanks Erm.
This circuit seem to be very simple… and can be used on modern technologie.

On a Bluetooth card, for exemple…
SignalClean2.jpg
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