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TRS 80 cassette recorder emulator idea

taylorjpt

taylorjpt

Experienced Member
Joined
Oct 26, 2023
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75
I Just repaired my TRS80 PC2 and got a cassette recorder from Amazon to test that functionality but immediately started thinking about making an emulator that could be used to save and load to a flash file system. I'm thinking stand alone with a usb C for the lipo charger and connection to a PC. Maybe a display and a scroll wheel to select the program to load etc. I figure I could put an infinite number of programs on these 32Gb flash chips.

Has anyone seen such a thing or do I have to make my own?
 
Isn't that basically a MP3 player? There are some dedicated devices for other systems. I remember seeing one over on The Spectrum Show. https://theretrohacker.com/2022/03/02/lets-build-retro-edition-the-tzxduino-reloaded/ I don't know how much work it would take to add PC2 audio output to the base design.

Or for inspiration for something a bit more complex, https://www.tramsoft.ch/sharp_erweiterungen/index_en.html#parallel-floppy_1500 I don't know if anyone could find one now but combined with a Commodore 1541 flash emulator would provide about 90% of what you want immediately.
 
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As this is your first post - welcome to VCFED.

There are plenty of these 'cassette emulators' around that have been developed by individuals for various machines.

I second the cation about MP3 players.

Keep having the good ideas though!

Dave
 
I've had luck with one of those personal recorders. I've got a sony one with jacks on the top and once I figured out how to make it record and playback WAV files and got the volume correct, it works fine.

I had at one point also tried to make (but didn't finish) a microcontroller project that would convert the audto to digital and vice versa, not to wav, but to a digital program file like you see emulators use. Such a thing would be specific to a type of system though.
 
64kbps MP3 will be more than adequate. It's 1500bps square waves, fidelity's not all that important. Playback volume will have a way bigger effect than compression artifacts. :p
 
I've been thinking of soldering together a breakout for a standard phone earbud/headset jack that splits it into a mono out and a properly attenuated line/mic input. (People have gotten away forever with plugging the TRS-80's output plug into recorder Mic jacks, but technically it's line-out and "too hot" for a Mic plug.) Everyone's got a smartphone today, right? And if you're worried about compression there are recorder apps that can do .wav or other lossless formats.
 
oktology said:
64kbps MP3 will be more than adequate. It's 1500bps square waves, fidelity's not all that important. Playback volume will have a way bigger effect than compression artifacts. :p
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I've run into trouble with MP3 and other compressions before. As I recall MP3 encoded Model III (1500 baud) cassette audio wouldn't load but 500 baud Model I would. I think even as high as 192 kb/s.

I had similar problems with putting cassette audio into a youtube video.

I made some effort to understand exactly why the MP3 encoding damaged the signal but couldn't figure it out. Possibly because figuring out cassette load problems brought back too many unpleasant memories of struggling with cassette load/save back in the day.
 
When I have thought about a TRS-80 M1 cassette emulator/player, I think about the old data dubber. Basically just some Schmitt triggers for wave shaping and some other stuff. I have one and, as I recall, they worked quite well. Then of course some lossless encoding scheme.

I guess I would first do a thorough search for what has already been done. Then again, I don't think about it too much.

​

 
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I used one of these to transfer data by cassette from remote dataloggers to PCs back in the day. Just found one on eBay and bought it.

s-l1600.jpg
 
oktology said:
19.2kbps from a cassette?? Incredible!
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Not all that incredible. Some of the Cambell Scientific systems have an 8-bit CPU to handle the cassette port and a large amount of memory to buffer between the cassette and the computer. So its 19.2 kbps between interface and computer but only 10kbps to the cassette using high density format and I think about 2400 bps with the older low density cassette format.
 
krebizfan said:
Not all that incredible. Some of the Cambell Scientific systems have an 8-bit CPU to handle the cassette port and a large amount of memory to buffer between the cassette and the computer. So its 19.2 kbps between interface and computer but only 10kbps to the cassette using high density format and I think about 2400 bps with the older low density cassette format.
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That sounds about right.
 
exidyboy said:
This is completely untrue.
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I'd agree that compression isn't great, given the potential for all kinds of mangling. But on the flip side even a fairly low bitrate .WAV file will probably be okay. I'm not sure about the Tandy Pocket computers, but according the TRS-80 Model III tech manual the highest audio frequency produced by the 1500 baud circuitry in that machine is 2,680hz. Using the standard rule of thumb even a 6khz .wav should be effectively lossless. So, yeah, I'd recommend using a device that can do uncompressed audio over .mp3, but even with that restriction even a pretty small by today's standards flash disk should be plenty large.
 
The PC-1500 has several tape formats. Pocket Tools indicates that QuickTape has a base frequency of 5 kHz, double that of the standard PC-1500. 10kHz WAV might be a better floor. BIN2WAV does the output at 44.1 kHz for the PC-1500. Might not be the most efficient but presumably works fairly well.

I don't know if the PC2 implemented all the features of the PC-1500.
 
The CE-150 manual has a description of the PC-1500/PC-2 standard cassette format. It looks very similar to the Kansas City standard with each bit needing multiple cycles. This is going to be very slow but should be reliable even against very poor audio devices.

When the contents of the start bit or data bit is "O", four pulses of 1.27kHz are recorded in a time
of 3 .l 5ms. When the contents of the data bit is "1 ", eight pulses of 2.54kHz are recorded in the
tape in a time of 3. l 5ms.
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There is a diagram below that shows the extra bits needed. Each 4 bits of data follow a start bit with the value of 0 and is followed by two bits with the value of 1 acting as a stop bit. Start off at about 300 bps and have almost half the data transferred be overhead. If I did the math right, that means saving the contents of a 16K memory card is going to take about 15 minutes.
 
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I use my old iphone 6 to store .wav and an occasional MP3 files for my CoCo, MC-10, and Model 100. Once the volume is figured out, it works fine, or at least as well as I remember cassettes working. I don't have a cassette interface for any of my pocket computers yet, so this may not to pertain to the topic.

J White
 
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