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Forum Index : Microcontroller and PC projects : 980's data recorders (as used in Commodore etc) - on topic really.
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Nimue Guru  Joined: 06/08/2020 Location: United KingdomPosts: 420 |
edit -- subject should say 1980's -- Hi all Something has been "bothering" me for a while and I thought I'd start to look into it a bit. I'm not an audiophile by any measure, but I do like 1970's and 1980's "audio" kit -- reel to reel and cassette players mostly. BUT most cassette players post 1980 are fairly "poor" -- and by that I mean as as cheap as possible and audio quality was not their prime concern. I also have an ANF03 (used with BBC kit) and a C2N used with Commodore kit. These where designed to be used as computer datarecorders. As such presumably they were designed to be more "stable" so that the data would record and play back more reliably. So question: I wonder if a datarecorder built in the 1980's is "better" at playing audio than a cheap 1980's audio player? With that in mind I'm off to build some kit to test it. Back on topic.... CMM2 related: What would I need to "do" to use the audio out as a vehicle to save MMBasic to tape? Edited 2021-08-20 00:01 by Nimue Entropy is not what it used to be |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7938 |
The on-topic bit first... :) The conventional way to store data to cassette tape is the "Kansas City Format". You *may* be able to do this in PWM now, but I really wouldn't recommend it unless your programs are short! The original standard is for 300baud, but I've had one running reliably at up to 2400baud on the Nascom. The version I had was a pcb that you just connect to a suitably set up UART. The Commodore C2N wasn't a great device. The main thing in its favour was that Commodore supplied their engineers with an alignment cassette so they all went out the same. I don't know the ANF03 at all. Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2170 |
Hey Nim, nice to see you posting again. you may have difficulties with the timings even on a fast system with interpreted language. I was watching Noel look into this the other day and although this was on old amstrad CPC machines, it was a fascinating insight to the intricasies of writing/reading ddata from tape. It might act as a nice "primer" before you embark on this voyage. You can watch it here https://www.youtube.com/watch?v=MAIsOIwgJWA If it adds nothing it's still a nice nostalgia trip just to hear it again.  |
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jirsoft Guru Joined: 18/09/2020 Location: Czech RepublicPosts: 533 |
C2N is for sure good choice, as is "partially" digital. But you need 9V to power the motor... Jiri Napoleon Commander and SimplEd for CMM2 (GitHub), CMM2.fun |
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| Nimue Guru Joined: 06/08/2020 Location: United KingdomPosts: 420 |
Video queued for this evening. Glad to be back - Covid + long Covid is a real pain in the lungs ;-) -> the only up side has been 3 months off work!! I'll keep chipping away and post back. Cheers N Entropy is not what it used to be |
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| Nimue Guru Joined: 06/08/2020 Location: United KingdomPosts: 420 |
Can I get straight audio out? N Entropy is not what it used to be |
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| Nimue Guru Joined: 06/08/2020 Location: United KingdomPosts: 420 |
Really just looking at proof of concept -- would be good to show students how this "used to work" without me lugging my Electron around. N Entropy is not what it used to be |
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| jirsoft Guru Joined: 18/09/2020 Location: Czech RepublicPosts: 533 |
In Commodore recorders signals are digital, so you will get audio clamped by integrated A/D convertor. Cassettte Port So good for data, bad for audio... Jiri Napoleon Commander and SimplEd for CMM2 (GitHub), CMM2.fun |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7938 |
There's no way to get audio out of a C2N as standard. The decoding is done inside and the interface is all TTL. http://www.zimmers.net/anonftp/pub/cbm/schematics/datassette/index.html Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| jirsoft Guru Joined: 18/09/2020 Location: Czech RepublicPosts: 533 |
I expect, when you will use old (slow) C64 data format, it should be possible with MMBasic (data read and write, not pure audio). Edited 2021-08-20 00:15 by jirsoft Jiri Napoleon Commander and SimplEd for CMM2 (GitHub), CMM2.fun |
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| CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2170 |
gawd! sorry to hear you been poorly... perhaps we should have a role-call thread in "other stuff" - I noticed loads of names have dropped off the radar... Let's just hope it's that they have nothing to say/contribute. |
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| Nimue Guru Joined: 06/08/2020 Location: United KingdomPosts: 420 |
Great link... From the schematics, if I tap the siganal before the A to D conversion I "might" be able to output analogue.... worth a go.... Thanks N Entropy is not what it used to be |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 7938 |
*If* the C2N has a stereo head then it will be wired as mono or single channel stereo, of course. I hope that long Covid has gone... Flippin' 'orrible thing to get stuck with. Edited 2021-08-20 01:11 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 5091 |
IF you want to restore programs from a cassette player, you need to do something we are not used to anymore: synchronize at every bit/byte (or be very tolerant). Current communication standards have very narrow timing tolerances, but cassette tape players vary in speed more. Appart from that audio levels fade, so you need to feed the audio output through a smitt-trigger input, and make it digital. Another thing to notice is that modulation on a cassette tape has to confirm to the audio bandwidth. So a RS232 signal cannot be recorded directly, since is has a DC component that varies with data content. Hence the "Kansas City Standard" type modulation. It is a nice experiment. I am pretty sure you can write the kansas standard in basic on a CMM2, and use a 74HC14 smitt trigger, AC coupled for input. A simple resistor divider for output. 300 Baud should be simple. And that would also work with a old-school stereo cassette deck (use only L or R channel, not both if you want to be able to play it back on another casette player). Volhout Edited 2021-08-20 01:43 by Volhout PicomiteVGA PETSCII ROBOTS |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2642 |
Re software on cassette. Stretching my memory a lot, I think the MicroBee used 1800Hz / 2400Hz dual tone system. The duration of one tone was the "clock" timing reference, in between the data tones. The duration of which (relative to the preceding "clock" tone) gave a 0 or 1. This allowed for speed variations during playback. Then again this may be from something else. Going senile. |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
Somewhere in the shed I have a few microbee tapes. I used a bog standard cassette player but lashed out on data grade tapes. I even found one on the bookshelf here.  Jim VK7JH MMedit |
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
My first encounter with datasettes was the Atari 1010 unit that I had originally with my Atari 800XL, up till I got so sick of tapes that I bought a disk-drive. It was something like $500 at the time - as expensive as the computer! The 1010 unit had a stereo tape head in it, and one channel was used for analog data, the other was used as a standard sound channel. That way, you could have tapes that included tuition spoken in English that the program could start and stop via commands. Quite clever I thought! I had one of those that died on me, and I DID turn it into a stereo cassette deck, by gutting the old Atari electronics out of it, and installing a tape-head pre-amp instead, then connected it to my stereo. The 1010 was not the best design mechanically either, and it was common for the cassette control buttons to break. Smoke makes things work. When the smoke gets out, it stops! |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 5091 |
Just remember the patience you must have writing and reading the tape. And searching for the start of your program when the mechanical counter was offset. I remember pressing "wind" and softly pressing "play" to move the head towards the tape during fast wind, so you could hear the silence between programs to locate the start. And when you where lucky the tape would stay intact.... At 300 baud, that is 30 characters per second. Mauro's last creation would take 4 hours to load (if you had a tape that long)..... Edited 2021-08-20 17:09 by Volhout PicomiteVGA PETSCII ROBOTS |
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| phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2642 |
Just for curiosity, it might be interesting to play one of those tapes into a PC with audio software such as Audacity to see what the data really looks like. My recollection above may not be right. |
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| TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6283 |
Unfortunately, the cassette from the cover I photographed is missing so I still have to search the shed. Then find a working cassette player. VK7JH MMedit |
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