Computer Nerd Kev
Projects > Tape Beeper
Commodore Datasette Tape Beeper
A while ago at the comp.sys.cbm newsgroup (yes I'm still typing in 2014, you new-fangled web forumers), a post was made asking if the schematic was available for the "PET Beeper", a device made in the 70s for the Commodore PET computer.
Here's the post:
Hi, there used to be a thing called the "PET Beeper". See here: http://rick-melick.blogspot.ch/2013/01/my-personal-electronic-transactor.html This small device would be plugged between the cassette connector of the computer and a datasette and would produce a small beep whenever a program was found on cassette or when loading ended. I think it would produce that beep whenever the motor stopped, but that's only my personal guess. Anyway, does anybody know if there are any schematics around? I didn't find any but would love to have such a thing. It would be very handy when loading long programs from datasette because you wouldn't actively have to wait and watch again and again but rather do something else and just wait for the beep. :-) -- cul8er Paul paul.foerster@xxxxxxx
For those who don't know (I'm not going to second guess my tiny audience here), these old computers could load programs from casette tapes. This made things very cheap, but also ended up enforcing that rule about taking a five minute break for every hour of computer use (ie. they were slow, really slow). The "PET Beeper" (which would also work with the later Commodore Vic-20, C64 and C128 computers which used the same tape drive interface) makes a beep sound when the data has been loaded, so you can stop contemplating whether machine is the slave of man or man the slave of machine and get back to work.
Unfortunately the schematics did not avail themselves from the pit of 70s electronics heritage, leaving the web page found by Paul Föerster as the only source for reference. So I sketched a circuit which does the same thing:
There are a few options depending on how you want it to function, and a simple alternative if it all looks too hard. Below is my post trying to describe what it all means:
wrote: On 2014-08-09 23:07:46 +0000, Computer Nerd Kev said: >>If the original schematics can't be found, it should be quite easy to >>design if it works on the motor control as you suspect. >well, at least that's how I understood the one page leaflet on that >website. I think it just beeps once whenever the motor stops, which >would IMHO suffice to get the desired effect. But then, I'm not that >much a hardware guru that I could design such a thing. I sketched this yesterday: http://www.computernerdkev.heliohost.org/tapebeep.gif [See Above] It has lots of options. The simple version is very easy to build and could be built "point-to-point" without a prototypeing board or PCB. The problem with it is that you need to manually turn it off to stop it buzzing when the file has loaded, so you then need to turn it on again once another file begins to load. The "trigger" sections of the more complicated versions are on the left of the page. "Timer" keeps the sound going for a period of 3 or 4 seconds, "Latch" runs it until someone comes over and presses a button to disable it, but will still turn it on again next time the motor goes from running to stopped. The output options are either a Buzzer (Don't need the diode if you buy a "pizo buzzer", but make sure you avoid buying a "pizo transducer" or the like as these need additional circuitry to make a buzz (which is built in with a "pizo buzzer"). or (as in the 70s device) an oscillator with a speaker, the frequency of which can be varied by adjusting VR1 (again like the 70s device). I expect the original device worked as this would with the "Timer" and "Speaker OUT" options used. Sounding for a few seconds after every load. None of these circuits have been tested by me, or particularly well looked over (also, I wasn't looking at the computer schematics when I did them, so there could be a very obvious flaw). Still, they should be in the right direction and if you build one, I'd love to hear about it. If you build one with the "Speaker Output", you can use a NE556 Dual Timer instead of two 555s. Here is my reference for the Datasette pinout, it includes wire colours: http://old.pinouts.ru/HD/petdatasette_pinout.shtml -- __ __ #_ < |\| |< _#
Paul Föerster then recreated my circuit in the "iCircuit" Mac simulation program, with the following result:
Of course it wasn't that simple and there was plenty of discussion to come to the final circuit. Quite a bit of that was trying to get it to work in Paul Föerster's simulator, but I also discovered a few mistakes in my first sketch (if you want to laugh, here's my original schematic). For the full intercontinental circuit confusion experiance, I present to you the original thread. Plus, for those of you playing along at home, here are the referenced images that I couldn't be bothered working into the thread archive, note that only the final versions as shown above on this page are fully functional designs:
And here are the files that Paul Föerster put in his "DropBox" folder: