28 Feb
2017
28 Feb
'17
7:55 a.m.
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
brain at jbrain.com
www.jbrain.com
28 Feb
28 Feb
7:59 a.m.
74hc(or ls)14
Enviado do meu Tele-Movel
On Feb 28, 2017 12:55 PM, "Jim Brain via cctalk" <cctalk at
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
brain at jbrain.com
www.jbrain.com
9:09 a.m.
74LS of 74HC gates are not going to work, the signal level is only 1V
the threshold for 74LS is 2V and for 74HC it is 3.7V. I would probably
use something like a compatator or an opamp but I don't have a circuit
handy to use, but tehy should be easy to find.
Paul.
On 2017-02-28 11:59 AM, Alexandre Souza via cctalk wrote:
74hc(or ls)14
Enviado do meu Tele-Movel
On Feb 28, 2017 12:55 PM, "Jim Brain via cctalk" <cctalk at
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
> brain at jbrain.com
> www.jbrain.com
>
>
10:08 a.m.
On 2/28/17 12:09 PM, Paul Berger via cctalk wrote:
74LS of 74HC gates are not going to work, the signal
level is only 1V
the threshold for 74LS is 2V and for 74HC it is 3.7V. I would
probably use something like a compatator or an opamp but I don't have
a circuit handy to use, but tehy should be easy to find.
Simply bias it in the middle of the range it works well then.
All digital circuits start as analog designs.
Paul.
On 2017-02-28 11:59 AM, Alexandre Souza via cctalk wrote:
74hc(or ls)14
Enviado do meu Tele-Movel
On Feb 28, 2017 12:55 PM, "Jim Brain via cctalk" <cctalk at
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
> brain at jbrain.com
> www.jbrain.com
>
>
8:21 a.m.
On 2/28/17 10:55 AM, Jim Brain via cctalk 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.
Why?
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>
The 339 is a very strange beast and can behave very badly. The 741 is
slow but should work as an amplifier and as a comparator
with minimal grief. Trying to use 339 or 714 circuits for each other
will usually fail as they behave differently.
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))
The tape recorders used had no agc. They were simple portables and used
the mic or line input and headphone output.
The big thing is most of those circuits took advantage of the audio out
of the recorder (low level and fairly low impedance)
easily but larger they would overload (sometimes badly).
The output was for a low level input and loading it usually lowers the
output more (high impedance source).
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.
Why not just go inside and grab the signal at it source before any of
the analog? it starts life at TTL waveforms (not 5V).
Why are you trying to get to 5V in the first place?
Allison
Jim
10:17 a.m.
On Tue, Feb 28, 2017 at 11:21 AM, allison via cctalk
<cctalk at classiccmp.org> wrote:
On 2/28/17 10:55 AM, Jim Brain via cctalk wrote:
It sounds like he is contemplating a battery-powered tape drive
emulator that plugs on the outside of the machine for users to use
without opening their boxes. It would then be portable to other
machines. Sounds like a great idea.
I have a cute idea for a cassette port project
for the Tandy line of
computers (the ones with the cassette port)....
Why not just go inside and grab the signal at it source before any of the
analog? it starts life at TTL waveforms (not 5V). Why are you trying to get to 5V in the first place?
Digital input to the AVR.
-ethan
10:36 a.m.
On 2/28/17 1:17 PM, Ethan Dicks via cctalk wrote:
Sounds more
complicated than need be.
AVR can measure small signals using the A/D and then do a bit of looking
for zeo crossing to
detect bit times.
Allison
On Tue, Feb 28, 2017 at 11:21 AM, allison via cctalk
<cctalk at classiccmp.org> wrote:
A sound recorder, how novel. My I phone and
androids already do that.
Before that I use tape recorders.
On 2/28/17 10:55 AM, Jim Brain via cctalk wrote:
It sounds like he is
contemplating a battery-powered tape drive
emulator that plugs on the outside of the machine for users to use
without opening their boxes. It would then be portable to other
machines. Sounds like a great idea. I have a cute idea for a cassette port project
for the Tandy line of
computers (the ones with the cassette port)....
Why not just go inside and grab the signal at it source before any of the
analog? it starts life at TTL waveforms (not 5V). Why are you
trying to get to 5V in the first place?
Digital input to the AVR. -ethan
11:08 a.m.
On 2/28/2017 12:36 PM, allison via cctalk wrote:
A sound recorder, how novel. My I phone and androids
already do that.
Before that I use tape recorders.
Using a classic machine, how novel. My iPhone
and androids already
compute everything I need. Before that I used other machines still more
capable than classic systems.
AVR can measure small signals using the A/D and then
do a bit of
looking for zeo crossing to
detect bit times.
Even that is too much work, since the AVR has an internal
comparator
(that will fire an interrupt on crossing), no need to measure voltage
levels. But, as I noted in the original email, I already tried that,
and did not have success.
Jim
--
Jim Brain
brain at jbrain.com
www.jbrain.com
10:43 a.m.
On 2/28/2017 12:17 PM, Ethan Dicks via cctalk wrote:
It sounds like he is contemplating a battery-powered
tape drive
emulator that plugs on the outside of the machine for users to use
without opening their boxes. It would then be portable to other
machines. Sounds like a great idea.
This year's CocoFEST is open to all TRS-80
models, not just the Coco,
and I noticed that many of the models have a similar cassette port
connector (I think they have variations on the format), and so I thought
of a neat project that might be of interest to all of the participants
of the show.
As you note, picking off 5V from inside, while entirely possible, is far
from optimal, and a uC is the intended recipient.
Besides, as Tony
implies, I should know this stuff, but I have indeed managed to
move
along in my efforts for so many years without needing to use a
comparator :-)
--
Jim Brain
brain at jbrain.com
www.jbrain.com
10:51 a.m.
On 2/28/17 1:43 PM, Jim Brain via cctalk wrote:
On 2/28/2017 12:17 PM, Ethan Dicks via cctalk wrote:
The TRS-80 used two formats! THe base 4K with 4K basic was a slower
format than the 12K basic machine.
The MM100 was a modem (bell 103 compatable).
The pocket computer was again different I forget the format.
COCOs I think were not all the same.
Lots of ground to cover.
Allison
It sounds like he is contemplating a
battery-powered tape drive
emulator that plugs on the outside of the machine for users to use
without opening their boxes. It would then be portable to other
machines. Sounds like a great idea.
This year's CocoFEST is open to all
TRS-80 models, not just the Coco,
and I noticed that many of the models have a similar cassette port
connector (I think they have variations on the format), and so I
thought of a neat project that might be of interest to all of the
participants of the show.
As you note, picking off 5V from inside, while
entirely possible, is
far from optimal, and a uC is the intended recipient. Besides, as
Tony implies, I should know this stuff, but I have indeed managed to
move along in my efforts for so many years without needing to use a
comparator :-)
2:03 p.m.
if anyone has a cable for the trs 80 model 100 small compact cassette drive to the 100
please lest us know. need this for demoing and display of the model 100 in the museum...
thanks ed# www.smecc.org
Sent from AOL Mobile Mail
On Tuesday, February 28, 2017 allison via cctalk <cctalk at classiccmp.org> wrote:
On 2/28/17 1:43 PM, Jim Brain via cctalk wrote:
On 2/28/2017 12:17 PM, Ethan Dicks via cctalk wrote:
The TRS-80 used two formats! THe base 4K with 4K basic was a slower
format than the 12K basic machine.
The MM100 was a modem (bell 103 compatable).
The pocket computer was again different I forget the format.
COCOs I think were not all the same.
Lots of ground to cover.
Allison
It sounds like he is contemplating a
battery-powered tape drive
emulator that plugs on the outside of the machine for users to use
without opening their boxes. It would then be portable to other
machines. Sounds like a great idea.
This year's CocoFEST is open to all TRS-80
models, not just the Coco,
and I noticed that many of the models have a similar cassette port
connector (I think they have variations on the format), and so I
thought of a neat project that might be of interest to all of the
participants of the show.
As you note, picking off 5V from inside, while
entirely possible, is
far from optimal, and a uC is the intended recipient. Besides, as
Tony implies, I should know this stuff, but I have indeed managed to
move along in my efforts for so many years without needing to use a
comparator :-)
11:35 a.m.
On Tue, 28 Feb 2017, Jim Brain via cctalk wrote:
This year's CocoFEST is open to all TRS-80 models,
not just the Coco, and I
noticed that many of the models have a similar cassette port connector
yes. even the IBM PC 5150 uses the same connector and pinout, and cable
(Radio Shack #26-1207)
(I think they have variations on the format),
for some meaning of "variation"
11:29 a.m.
On Tue, Feb 28, 2017 at 4:21 PM, allison via cctalk
<cctalk at classiccmp.org> wrote:
The tape recorders used had no agc. They were simple portables and used the
mic or line input and headphone output.
I have to disagree with you there. I have just looked at the documentation for a
couple of the Radio Shack tape recorders commonly used with TRS80s, and
both have automatic gain control on recording.
It is actually quite rare to see a simple portable cassette recorder which
doesn't have automatic gain control (automatic level control). The early
Philips machines like the EL3300 are the only ones I've come across.
-tony
12:02 p.m.
It was thus said that the Great Tony Duell via cctalk once stated:
On Tue, Feb 28, 2017 at 4:21 PM, allison via cctalk
<cctalk at classiccmp.org> wrote:
I recall using a normal casette tape recorder with my Coco back in the
day. I don't recall a gain control, but I do recall setting the volumn
control way up. Never had a problem reading back tapes.
-spc
The tape recorders used had no agc. They were simple portables and used the
mic or line input and headphone output.
I have to disagree with you there. I have just looked at the documentation for a
couple of the Radio Shack tape recorders commonly used with TRS80s, and
both have automatic gain control on recording. 
9:12 a.m.
On Feb 28, 2017, at 9:55 AM, Jim Brain via cctalk <cctalk at 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.
Warning, I am not an electrical engineer at all, only opinionated.
What about:
(analog out) -> A/D conversion -> tight software loop -> D/A conversion ->
(analog in) ?
Use a dedicated (Beaglebone? Raspberry Pi?) system in the middle, and o-scope the analogs
to make sure it?s clean enough.
The dedicated system should be able to 5V (or whatever you want) on the output, and I
would think be fast enough to generate a reasonable sine-wave coming out if it only has to
be audio frequencies.
Once you have it working that way (and the software loop should allow you to tune it at
will), you could build a simple dedicated circuit to multiply the same way the software
did.
This is killing a mosquito with a sledgehammer, I know. With any luck, one of the regulars
who *is* an EE will chime in before you read this with the correct answer, in which case
disregard.
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.
Can a plain transistor do both + - ways on voltage?
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.
Even if it did, this looks like it implies all square waves. I think CoCo is designed to
work with modulated sine-waves, and there could be some frequency components of the square
waves (3x frequency, etc) that are causing problems somewhere.
I don?t know that an AVR can run fast enough to do the sine-waves. I would guess you need
to sample and digitize at least 10 times faster than the carrier (so maybe 100kHz?) and
same for the output.
So, I finally decided a comparator solution would be
required.
Still square-wave? I could be on the wrong track here completely, but I?m thinking you
want sinewaves.
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
brain at jbrain.com
www.jbrain.com
- Mark
9:43 a.m.
On Tue, Feb 28, 2017 at 5:12 PM, Tapley, Mark via cctalk
<cctalk at classiccmp.org> wrote:
Oh for $deity's sake. Why does everyone now insist on using a million components
when a dozen will do? I stick to classic computers to get away from this. In any
case it won't help that much. You should have some analgue 'signal
conditioning'
circuitry before the ADC (to get the input signal into the right
voltage range for
the ADC), ditto after the DAC. Otherwise you are wasting the performance of said
converters.
To get back to the problem. What do you _actually_ want the output to become? An
analogue signal or a digital one?
An op-amp will boost the signal. Look at the LM324 (a very cheap and common
part, I have chosen it because the input voltage range goes down to 0 so you
can run it off a single 5V supply). You could use it as a *5 amplifier by adding
2 or 3 resistors.
If you want a digital signal then look at a comparator chip like the LM339. This
compares the voltages on the 2 inputs, the output changes state as they pass
each other (if you see what I mean). So you cassout signal to one
input, a stable
voltage of, say 0.5V on the other. There are couple of gotchas with
this chip. The
first is that it has open collector outputs, so you need a pullup
resistor. The second
is that it tends to oscillate at switchover. You can add hysteresis
with a couple
of resistors to prevent this.
Where do you get the 0.5V reference from? Well, if your 5V supply is stable you
can use that, divided down with a couple of resistors. Say 9.1k and 1k in series
across the supply, comparator input to the junction. Or perhaps 0.7V from a
forward biased silicon diode (diode cathode to ground, anode to +5V via a 4k7
or so resistor, take the 0.7V from the diode anode).
Do you have 'The Art of Electronics'? If not buy it. Yes, it's expensive But
it
explains all this and more.
-tony
On Feb 28, 2017, at 9:55 AM, Jim Brain via cctalk
<cctalk at classiccmp.org> wrote:
> Analog, which is my nemesis, curses me again.
I fail to see how anyone can be a good digital designer and not
understand analogue
electronics.
>
> 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.
That sounds about right. IIRC the CoCo 3 uses a custom chip that contains a
6 bit DAC for this. Older machines just use a couple of TTL output
port lines and
a few resistors. The CoCo3 service manual suggests the output is 1V peak-to-peak
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.
Warning, I am not an electrical engineer at all, only opinionated.
What about:
(analog out) -> A/D conversion -> tight software loop -> D/A conversion ->
(analog in) ? 
9:53 a.m.
On Tue, 28 Feb 2017, Tony Duell via cctalk wrote:
On Tue, Feb 28, 2017 at 5:12 PM, Tapley, Mark via
cctalk
<cctalk at classiccmp.org> wrote:
Fixed that for ya. :D
g.
--
Proud owner of F-15C 80-0007
http://www.f15sim.com - The only one of its kind.
http://www.diy-cockpits.org/coll - Go Collimated or Go Home.
Some people collect things for a hobby. Geeks collect hobbies.
ScarletDME - The red hot Data Management Environment
A Multi-Value database for the masses, not the classes.
http://scarlet.deltasoft.com - Get it _today_!
On Feb 28, 2017, at 9:55 AM, Jim Brain via cctalk
<cctalk at classiccmp.org> wrote:
> Analog, which is my nemesis, curses me again.
In my opinion, I fail to see how anyone can be a good digital designer
and not understand analog electronics.
10:10 a.m.
On 2/28/2017 11:43 AM, Tony Duell via cctalk wrote:
I fail to see how anyone can be a good digital
designer and not
understand analogue
electronics.
A couple points:
* It is entirely possible I am not a good digital designer
* I believe I have a basic understanding of analog, but I may not be
competent.
To get back to the problem. What do you _actually_
want the output to become? An
analogue signal or a digital one?
A digital one. The current goal is to feed the
incoming data stream
into an Atmel AVR running at 5V for parsing. The final goal is to do
the same, but run the AVR at 3V on two coin cells.
If you want a digital signal then look at a comparator chip like the LM339. This
compares the voltages on the 2 inputs, the output changes state as they pass
each other (if you see what I mean).
I understand the comparator function, though I
will admit I have rarely
used one. As I had some success on the AVR internal comparator circuit,
I was able to play around with the bias and see how it affected the output.
So you cassout signal to one
input, a stable
voltage of, say 0.5V on the other. There are couple of gotchas with
this chip. The
first is that it has open collector outputs, so you need a pullup
resistor. The second
is that it tends to oscillate at switchover. You can add hysteresis
with a couple
of resistors to prevent this.
I saw the notes in the datasheet about the
oscillation, and the
recommended way to overcome this. I also noticed the Coco 1 schematic
includes this exact recommendation. I then wired up the exact circuit,
using the LM339 from my Coco1, and the exact resistors and other
passives as specified in the schematic.
Where do you get the 0.5V reference from? Well, if your 5V supply is stable you
can use that, divided down with a couple of resistors. Say 9.1k and 1k in series
across the supply, comparator input to the junction.
The Coco1 creates a 1.05V
reference via the 15K and 56K resistors. After
I noticed that the analog signal was centered around .5V, I quickly
added another 15K resistor in parallel with the first one, to create a
56K/7.5K divider, which yields .591V as a reference. I am using a lab
PSU, running at 5.00V, but the resulting circuit did not respond to
changes in the Coco cassette data signal. I rechecked my circuit last
night, but will recheck it tonight in case I made some stupid wiring
mistake.
Jim
--
Jim Brain
brain at jbrain.com
www.jbrain.com
11:24 a.m.
On Tue, Feb 28, 2017 at 6:10 PM, Jim Brain <brain at jbrain.com> wrote:
[Comparators]
A digital one. The current goal is to feed the
incoming data stream into an
Atmel AVR running at 5V for parsing. The final goal is to do the same, but
run the AVR at 3V on two coin cells.
OK. I assume you don't want to be running special software on the CoCo, since
there are easier places to get a digital signal from if you can run
special software
(such as the RS232 port).
I saw the notes in the datasheet about the
oscillation, and the recommended
way to overcome this. I also noticed the Coco 1 schematic includes this
Yes, they do oscillate with the slightest provocation....
exact recommendation. I then wired up the exact
circuit, using the LM339
from my Coco1, and the exact resistors and other passives as specified in
the schematic.
Where do you get the 0.5V reference from? Well, if your 5V supply is stable
you
can use that, divided down with a couple of resistors. Say 9.1k and 1k in
series
across the supply, comparator input to the junction.
The Coco1 creates a 1.05V reference via the 15K and 56K resistors. After I
noticed that the analog signal was centered around .5V, I quickly added
another 15K resistor in parallel with the first one, to create a 56K/7.5K
divider, which yields .591V as a reference. I am using a lab PSU, running
at 5.00V, but the resulting circuit did not respond to changes in the Coco
cassette data signal. I rechecked my circuit last night, but will recheck
it tonight in case I made some stupid wiring mistake.
OK... Time to check the obvous. Firstly you have power to the comparator
chip (Easily forgotten, I speak from experience). You have a pull-up resistor
(say 1k, or 4k7) from the comparator output to +5V.
Now measure the output of that resistor divider. Make sure it _is_ 0.6V or
so. Use a 'scope in DC coupled mode (you do not want to lose the DC
level of the signal by using AC coupling) to look at the signal from the
CoCo on the other comparator input.
-tony
9:42 a.m.
* On Tue, Feb 28, 2017 at 09:55:30AM -0600, Jim Brain via cctalk <cctalk at
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.
Hi Jim,
When I was building a cassette circuit for my homebrew 6502 computer,
I essentially stole the Synertek SYM-1 circuit wholesale. See:
http://www.loomcom.com/blog/2013/01/04/retrochallenge-update-comparator-vs-…
http://www.loomcom.com/blog/2013/01/05/comparator-success/
Synertek used an LM311 (an LM358 would work just fine) to build a
comparator circuit. I _think_ you could use this exact circuit to
take the analog output from the CoCo and turn it into a 5V sqauare
wave.
-Seth
9:56 a.m.
On 02/28/2017 09:42 AM, Seth Morabito via cctalk wrote:
Synertek used an LM311 (an LM358 would work just fine)
to build a
comparator circuit. I _think_ you could use this exact circuit to
take the analog output from the CoCo and turn it into a 5V sqauare
wave.
I don't know a thing about the CoCo cassette format. I know that back
in the day when things like the KC standard were the rage, a NE567 PLL
was considered the cat's whiskers for data recovery. But again, I don't
know what the CoCo cassette standard looks like.
Also, you may want to look at the IBM 5150 (PC) cassette circuit. My
recollection was that it was pretty robust, even if few made use of the
facility.
--Chuck
10:14 a.m.
On 2/28/17 12:56 PM, Chuck Guzis via cctalk wrote:
On 02/28/2017 09:42 AM, Seth Morabito via cctalk
wrote:
Only works for FM and frequency
shift based formats.
Everyone had their own favorite. I used to flip a bit doing biphase in
software
at 2400 baud. Minimal parts to none.
Allison
Synertek used an LM311 (an LM358 would work just
fine) to build a
comparator circuit. I _think_ you could use this exact circuit to
take the analog output from the CoCo and turn it into a 5V sqauare
wave.
I don't know a thing about the CoCo cassette format. I know that back
in the day when things like the KC standard were the rage, a NE567 PLL
was considered the cat's whiskers for data recovery. But again, I don't
know what the CoCo cassette standard looks like Also, you may want to look at the IBM 5150 (PC)
cassette circuit. My
recollection was that it was pretty robust, even if few made use of the
facility.
--Chuck
10:39 a.m.
On 2/28/2017 11:56 AM, Chuck Guzis via cctalk wrote:
On 02/28/2017 09:42 AM, Seth Morabito via cctalk
wrote:
I admit my previous cassette
format knowledge is Commodore based, where
they basically shoved a 5V digital signal to the cassette deck, and
expected the deck (which they produced) to handle it. Thus, interfacing
with it is a digital exercise. But, I am not picky on circuitry, so I
will take a look. Any pointers to a schematic?
Synertek used an LM311 (an LM358 would work just
fine) to build a
comparator circuit. I _think_ you could use this exact circuit to
take the analog output from the CoCo and turn it into a 5V sqauare
wave.
I don't know a thing about the CoCo cassette format. I know that back
in the day when things like the KC standard were the rage, a NE567 PLL
was considered the cat's whiskers for data recovery. But again, I don't
know what the CoCo cassette standard looks like.
Also, you may want to look at the IBM 5150 (PC) cassette circuit. My
recollection was that it was pretty robust, even if few made use of the
facility.
I will do so. Right now, a success, even if it's not a final state
option, would be helpful. I had this great idea, but held off on it for
a few weeks because I suspected I'd end up in this state...
--Chuck
--
Jim Brain
brain at jbrain.com
www.jbrain.com
10:50 a.m.
On 2/28/2017 11:42 AM, Seth Morabito via cctalk wrote:
Hi Jim,
When I was building a cassette circuit for my homebrew 6502 computer,
I essentially stole the Synertek SYM-1 circuit wholesale. See:
http://www.loomcom.com/blog/2013/01/04/retrochallenge-update-comparator-vs-…
http://www.loomcom.com/blog/2013/01/05/comparator-success/
Synertek used an LM311 (an LM358 would work just fine) to build a
comparator circuit. I _think_ you could use this exact circuit to
take the analog output from the CoCo and turn it into a 5V sqauare
wave.
I will give it a try. Obviously, I'll need to reset the bias down to
.5V from 2.5V in your design, but I can do that. I notice the design
has no feedback, but has R93 feeding the reference into the inverting
input. Any idea what the function of that resistor is?
Jim
10:06 a.m.
Now that I read your whole email I would like to ask what you plan to do
with this boosted signal? I have never had a CoCo, but most cassette
interfaces on these old computers pretty much all worked like a modem
but you where recording the signal instead of sending it down a phone line.
From what I read the CoCo uses 1200Hz for zero and 2400 Hz for one,
what I was reading also went on to claim that it is a single cycle of
the tone to represent a bit. If you intend to feed this into a computer
converting the signal to a square wave would be ok as long as the
software monitoring the port had a high enough sampling rate to be able
to differentiate the width of the pulses, which should not be hard as
one is twice as long as the other. A comparator would be the best way
to produce a square wave representation, as they normally have a sharp
threshold which you would want to adjust so that it switches over at
about the 50% level of the input signal. If you have a dual channel
scope you can compare the input signal to the output to see if that is
what is happening. That might be hard to see on an analog scope, this
is where a storage scope or a digital scope comes in handy because you
can freeze the signal.
Paul.
On 2017-02-28 11:55 AM, Jim Brain via cctalk 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
12:34 p.m.
On 2017-Feb-28, at 7:55 AM, Jim Brain via cctalk 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.
In answer to the final point, and the interests of some analog education, looking at your
reffed pdf, page 75, the reason (or one reason)
your duplicated Coco input circuit is not working is the gross impedance mismatch between
the coco tape output and input circuits.
The output is high impedance: a 75K/24K voltage divider.
The input is quite low impedance: a 220-ohm resistor to GND right at the front.
When you connect them together they form another voltage divider which drops the coco tape
output down to a few millivolts across
the 220-ohm R, which then is the input to the 339 comparator (pin 10).
The trip point for the comparator is set at 1.05V by the 56K/15K voltage divider at pin
11.
If you want to play with the 339 comparator circuit, you could try adjusting the
comparator trip point voltage divider
(replace one of the 56K/15K appropriately) to get, say, 0.25V at pin 11;
strip away all the input stuff at pin 10 and feed it directly from the tape output.
(Could be a good exercise, watching the 399 output along with the tape output on a 2-chan
scope).
Using the internal AVR comparator sounds like a better final solution (fewer components),
but in devising an
input circuit for the AVR you may be running into the same issue of loading a
high-impedance source.
The 8.2K/6.8K R divider in the rakettitiede AVR circuit you tried is still quite disparate
to the coco tape output and will load it,
reducing the level seen by the AVR comparator. The blocking cap and biasing also changes
the levels you would be looking for at the comparator.
You could try multiplying the Rs of that divider up into the 10-100Ks range (probably best
to reduce the 0.47 shunting C by a similar factor or more).
However, considering you have a known and fixed source circuit (the coco tape output) you
might try something even simpler for the
AVR comparator input, such as just a 1K series R followed by a 220K to 470K R to GND. The
comparator should then be seeing essentially the coco output
wave shape and levels, without you having to adjust the software detection for biasing
introduced by the input circuit.
(This topic reminds me of my first assembly program as a teenager in the 70s, to make tape
storage for a MEK 6800 SBC.
I wanted to keep the hardware as minimal as possible and did pretty much the same thing, R
divider to drive to the tape, simple comparator
to digitise the sig from tape, simple encoding scheme with different pulse widths for 0/1,
and timing loops in software to produce and detect the pulse widths.)
10:40 p.m.
On 2/28/2017 2:34 PM, Brent Hilpert wrote:
In answer to the final point, and the interests of
some analog education, looking at your reffed pdf, page 75, the reason (or one reason)
your duplicated Coco input circuit is not working is the gross impedance mismatch between
the coco tape output and input circuits.
To get to the point, this advice was
golden. After stripping away the
220, 8K2,6K8 and the 56K to Vcc, the unit started functioning. A nasty
60Hz blip was removed by slightly biasing the negative input with a 1M
resistor to GND. The 1M drive to ground pulled the input over so much
lower, making the center around .7V, so I used Tony's idea to create a
.7V reference on the + end with a forward biased diode and a week pullup
to Vcc, which made things ever so much better.
Obviously, given the LM339 issues, this is unworkable in the end, but it
did get me to realizing some outputs on the LM339, so thanks to both of
you.
I can plainly see the oscillation on the comparator transitions, so it
is obvious I need a better comparator. I'll have to source a few
different comparator options from Digikey to fill my parts box.
Suggestions are welcome.
Using the internal AVR comparator sounds like a better
final solution (fewer components), but in devising an
input circuit for the AVR you may be running into the same issue of loading a
high-impedance source.
Though it plays into Tonly's notes about my analog
understanding (or
lack thereof), I was so disillusioned by the analog uncertainties that I
initial focused on the AVR comparator. By correctly biasing the
comparator, I was able to get much better results tonight, but the lack
of any ability to add hysteresis into the design hindered my success.
At transition, the signal simply bounces badly. I tried to construct a
low pass filter (22pF and 5K6), and some variations, but I was not able
to overcome. I then tried to deal with it in SW, but I have not yet
been successful. I'll try again, but lack of hysteresis is a big issue.
However, considering you have a known and fixed source circuit (the coco tape output) you
might try something even simpler for the
AVR comparator input, such as just a 1K series R followed by a 220K to 470K R to GND. The
comparator should then be seeing essentially the coco output
wave shape and levels, without you having to adjust the software detection for biasing
introduced by the input circuit.
I will try this tomorrow.
Jim
--
Jim Brain
brain at jbrain.com
www.jbrain.com
1 Mar
1 Mar
3:10 a.m.
On 03/01/2017 01:40 AM, Jim Brain via cctalk wrote:
Single transistor audio amp before it.
Allison
On 2/28/2017 2:34 PM, Brent Hilpert wrote:
snippage
Obviously, given the LM339 issues, this is unworkable
in the end, but
it did get me to realizing some outputs on the LM339, so thanks to
both of you.
I can plainly see the oscillation on the comparator transitions, so it
is obvious I need a better comparator. I'll have to source a few
different comparator options from Digikey to fill my parts box.
Suggestions are welcome.
OR a bit of positive feedback.
Using the
internal AVR comparator sounds like a better final solution
(fewer components), but in devising an
input circuit for the AVR you may be running into the same issue of
loading a high-impedance source.
Though it plays into Tonly's notes about my
analog understanding (or
lack thereof), I was so disillusioned by the analog uncertainties that
I initial focused on the AVR comparator. By correctly biasing the
comparator, I was able to get much better results tonight, but the
lack of any ability to add hysteresis into the design hindered my
success. At transition, the signal simply bounces badly. I tried to
construct a low pass filter (22pF and 5K6), and some variations, but I
was not able to overcome. I then tried to deal with it in SW, but I
have not yet been successful. I'll try again, but lack of hysteresis
is a big issue.
Jim
9:56 a.m.
I'm not sure how something as simple as a cassette interface could be causing so much
issues.
Can you post a schematic of what you have now and what the signal amplitude is?
Dwight
________________________________
From: cctalk <cctalk-bounces at classiccmp.org> on behalf of allison via cctalk
<cctalk at classiccmp.org>
Sent: Wednesday, March 1, 2017 3:10:50 AM
To: cctalk at classiccmp.org
Subject: Re: Cassette Interface Assistance
On 03/01/2017 01:40 AM, Jim Brain via cctalk wrote:
Single transistor audio amp before it.
Allison
On 2/28/2017 2:34 PM, Brent Hilpert wrote:
snippage
Obviously, given the LM339 issues, this is unworkable
in the end, but
it did get me to realizing some outputs on the LM339, so thanks to
both of you.
I can plainly see the oscillation on the comparator transitions, so it
is obvious I need a better comparator. I'll have to source a few
different comparator options from Digikey to fill my parts box.
Suggestions are welcome.
OR a bit of positive feedback.
Using the
internal AVR comparator sounds like a better final solution
(fewer components), but in devising an
input circuit for the AVR you may be running into the same issue of
loading a high-impedance source.
Though it plays into Tonly's notes about my
analog understanding (or
lack thereof), I was so disillusioned by the analog uncertainties that
I initial focused on the AVR comparator. By correctly biasing the
comparator, I was able to get much better results tonight, but the
lack of any ability to add hysteresis into the design hindered my
success. At transition, the signal simply bounces badly. I tried to
construct a low pass filter (22pF and 5K6), and some variations, but I
was not able to overcome. I then tried to deal with it in SW, but I
have not yet been successful. I'll try again, but lack of hysteresis
is a big issue.
Jim
5:40 p.m.
On 3/1/2017 11:56 AM, dwight via cctalk wrote:
I'm not sure how something as simple as a cassette
interface could be causing so much issues.
Can you post a schematic of what you have now and what the signal amplitude is?
Hmm, It's currently a jumble of wires and clips and such on the bench.
I'll see if I can make some sense of it.
Jim
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