Cassette interface?

[Robb Bates]

Does one exist for the RC2014?

Nothing pops up that's obvious other than Dean's MSX board.  I'm not sure if that will work on a straight Zed Pro.

Robb

[Robb Bates]

Or even just a stand alone cassette to serial interface.

Robb

[Alan Cox]

On Tue, 7 Oct 2025 at 20:29, Robb Bates <robb...@gmail.com> wrote:

Or even just a stand alone cassette to serial interface.

You don't need much more than a zener diode and a few resistors (ask Sinclair ;))

For a fancy one look here.

https://www.waveguide.se/?article=storing-data-on-cassettes

you just need the right hand bit then feed it into a Z80PIO or GPIO card or similar.

 

[Robb Bates]

This looks simple enough.  And I probably have all the parts in my bins.  I'll give it a shot.

https://maker.pro/pcb/projects/make-uart-cassette-tape-interface

Robb

[Peter Onion]

On Tue, 2025-10-07 at 12:09 -0700, Robb Bates wrote:
> Does one exist for the RC2014?
>

It's another thing on the list for my 3CX board (3CX = Orton 3C port eXpander).

In the distant past I built one with a op-amp schmitt trigger and a few Rs and Cs.

Currently I'm writing the code for load and save on a serial port using Motorola SRecords
:-)

PeterO

[MartinR]

Many years ago I had a Nascom2. The cassette interface was rock solid at 2.4kbps, though slower rates were configurable - and it conformed to the Kansas City Standard. That might be a good as a starting point, and the circuit diagrams are readily available online:

          https://80bus.co.uk.mirror.jloh.de/pages/nascom/documentation/Nascom2_Circuit.pdf

          http://www.nascomhomepage.com/pdf/Nascom2.pdf

MartinR

[Robb Bates]

I made this circuit.

https://maker.pro/pcb/projects/make-uart-cassette-tape-interface

And it works pretty well!

https://youtu.be/zGJamwuU09g

I'll most likely create a PCB and post the design here for others.

Pretty much just a cassette to TTL serial converter.  Useable for just about anything you can input and output to a terminal.  Saving BASIC programs by just listing them may be a problem because you can't do any flow control, so the needed delay after entering a BASIC line isn't going to be there, so the interpreter will miss some characters while it's processing the previously entered line.  Perhaps some modification of the BASIC source code to enable the SAVE and LOAD function could take care of that somehow.

You can get around that by using the character and line delay on TeraTerm to dump the data to the cassette somehow.

Anyway, pretty happy with the results.  It's only 300 baud at the moment.  I'm going to start fiddling with the values to try to get 1200 baud working.  I don't think it would handle anything much faster.  Maybe 2400, but then you're already pushing the limits of cassette audio bandwidth as it uses a 4800Hz carrier.

It's not KCS compatible, but to be honest, so many vintage cassette formats weren't either.  As long as I can save and load data using it, I'm happy.

Robb

[Phil G]

inho the Cottis-Blandford cassette interface can't be bettered. Mine is 47 years old and still works fine at 2400. 

Theres little more to it than the makerpro circuit, with no fancy chips, straight cmos logic and a pll for clock recovery (which can be omitted if your recorder is stable).

Nascom adopted it for the Nascom-2.   As well as for saving listings to tape mine spent a couple of years talking amateur packet radio (Cambridge System)

Its documented everywhere as it was published in Byte, PCW,  ACC newsletter etc  :-) and Mike is still around.

[Peter Onion]

I've found these two listings from ~1980 when I was building small Z80 systems.  They might be useful for my Orton 3C.

PeterO 

[Derek Cooper]

Hi rob,

Have you got a readable version of the schematic I try to click download full res version and it does not work. I can't read the values on the "how to make " web site.

Thanks

[Robb Bates]

If you zoom into the one that's there (CTRL scroll wheel), it's legible enough.  Or right click and open image in new tab.  And the BOM is listed above.

Here's the image copy pasted below.  It's clearer without the bad formatting.

If you want to build this yourself, a few tips:

You need to use a single supply op-amp.  A dual supply op-amp like a 741 won't work.  And I used a 2N3904 NPN transistor.  I also skipped the 100 ohm series resistors at the FTDI connector.  Also, adding a decoupling cap on each chip couldn't hurt.

As Phil mentioned above, there are better circuits.  This one certainly works, but I've found it can get out of sync.  i.e. if you start playback mid-byte and don't have enough space between bytes, your serial interface can't tell where one byte stops and the next begins.  But it does the job.

Robb