74hc(or ls)14 Enviado do meu Tele-Movel
On Feb 28, 2017 12:55 PM, "Jim Brain via cctalk" <cctalk@classiccmp.org> wrote: > Analog, which is my nemesis, curses me again. > > I have a cute idea for a cassette port project for the Tandy line of > computers (the ones with the cassette port). I have a Coco 3 on the bench, > so I scoped the output line while doing 'csave "jim"'. The signal looks to > be just under 1V PtP (0-1V on the scope), and rests at about .3V when not > sending data. > > I have tried 6 different ways to boost the signal to 5V digital, to no > avail, and so I ask humbly if someone with analog knowledge might be able > to assist. > > I first tried to boost the signal with a transistor (with variations using > a N channel FET as well). Arguably, that was foolhardy, and it did not work. > > My second attempt was based on this link that was shared with me: > > http://labs.rakettitiede.com/12kbps-simple-audio-data-transfer-for-avr/ > > The output from the Coco3 does not appear to be "loud" enough to work with > this circuit. > > So, I finally decided a comparator solution would be required. > > First, I tried a design using a 741 op-amp, which failed miserably, but > probably would have worked, but I tried to merge the design from the Coco1, > and replace the LM339 in the Coco 1 design with the 741, and I feel I did > not merge the designs well :-) > > I then tried using the comparator in an Atmel AVR, and had minimal > success. By biasing one input via a variable resistor to around .8V, I was > able to get a digital stream, but it did not look like the data stream of > the cassette format. > > I then pried an LM339 out of my Coco1 and replicated the circuit int the > Coco 1, as noted in the tech manual: > Color Computer Technical Reference Manual (Tandy).pdf < > http://www.colorcomputerarchive.com/coco/Documents/Manuals/ > Hardware/Color%20Computer%20Technical%20Reference% > 20Manual%20%28Tandy%29.pdf> > > I was shocked that I had no success with that design at all. I assumed > (wrongly, it appears) that the Coco cassette input circuit would read the > output of it's output circuit. Beyond the possibility that my components > are defective or I wired it up wrongly, I can only theorize that Tandy > assumed that all tape recorders would AGC the output and then feed a 2V PtP > signal back to the Coco (the Coco 1 circuit looks to bias the comparator at > 1.05V (not sure about the feedback resistor's impact)) > > I can fiddle around with the AVR solution, which might work if I can > smooth out the spikes and bias the comparator right, but it just bothers me > that the Coco 1 circuit does not work, as I assumed I would at least have > success by copying a working design. > > Jim > > > > -- > Jim Brain > br...@jbrain.com > www.jbrain.com > >
