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Those 555's are being used as voltage comparators and in a Schmitt trigger operation. A hole will shine light on a photo transistor, the voltage will drop below the "Trigger" voltage of the 555 and it's output will go high. When light does not shine on the PT, the voltage will rise to above the "Threshold" input and the output will then go low.
Don, I would start with finding the right Photo Transistor. You can't go any further without the sensing device. A look at Digikey reveals a decent option to be p/n BPW16N-ND. All other PT's are too big. You need to put these side by side, and the pitch is 0.1" (2.54mm) So even the 3mm PT's are too big. There are 9 holes, 8 data and 1 for the track (which is used to clock the data). That track hole is always much smaller, about 1/2 the size. This way, when it gets light, all the data PT's have already been given light (this is like the Setup Time). Also, when it looses the light, all the data PT's will still have light (hold time). I would start this design by putting all those PT's on a perf board, 9 wide at 0.1" apart. Then seeing what sort of pull up resistors you can get away with (higher the better). Cheers, Josh > Date: Wed, 11 Feb 2015 22:01:24 -0500 > Subject: Re: [N8VEM-S100:6307] Paper Tape Reader Project > From: rich...@verizon.net > To: n8vem...@googlegroups.com > > Bad pin countŠthose aren¹t optoisolators, but rather 555 timers. There¹s > probably a better way with flip-flops. > > Rich > > -- > Rich Cini > Collector of Classic Computers > Build Master and lead engineer, Altair32 Emulator > http://www.classiccmp.org/cini > http://www.classiccmp.org/altair32 > > > > > On 2/11/15, 9:59 PM, "Richard Cini" <ric...@verizon.net> wrote: > > >I think the OP-80A is the ³template² paper tape reader: > > > >http://www.swtpc.com/mholley/OAE80_Reader/OAE80_Index.htm > > > >I didn¹t look at the manual, and maybe the optoisolators are overkill, > >but > >at least it¹s a start. > > > >Rich > > > >-- > >Rich Cini > >Collector of Classic Computers > >Build Master and lead engineer, Altair32 Emulator > >http://www.classiccmp.org/cini > >http://www.classiccmp.org/altair32 > > > > > > > > > >On 2/11/15, 9:48 PM, "Don Caprio" <il...@gmail.com> wrote: > > > >>I've always wanted to build a simple paper tape reader. > >>But to be honest I'm not sure how to go about doing it. > >> > >>I've seen this one created by ipscone however emails go > >>unanswered. Looks like a very simple design. > >>I'm guessing just a LED array, some op amps and a couple TTL's. > >> > >>Anyone know of a schematic or would be willing to help me cook one up? > >> > >>http://youtube.com/watch?v=uZnuu18FtQk > >> > >>Thank you. > >> > >>-- > >>Don Caprio > >>...@gmail.com > >> > >>-- > >>You received this message because you are subscribed to the Google > >>Groups > >>"N8VEM-S100" group. > >>To unsubscribe from this group and stop receiving emails from it, send > >>an > >>email to n8vem-s100+...@googlegroups.com. > >>For more options, visit https://groups.google.com/d/optout. > > > -- > You received this message because you are subscribed to the Google Groups "N8VEM-S100" group. > To unsubscribe from this group and stop receiving emails from it, send an email to n8vem-s100+...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. |