-Original Message-
From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Brent
Hilpert
Sent: Sunday, August 23, 2015 3:07 AM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: RS-232 Tx / Rx monitoring LEDs?
On 2015-Aug-22, at 11:55 PM, drlegendre . wrote
On 2015-Aug-23, at 9:06 AM, Chuck Guzis wrote:
On 08/23/2015 07:10 AM, dwight wrote:
I've used the capacitor method to provide most of the drop in the
past. I don't usually max out the LEDs at 20ma. I find there is
little difference between 10 and 20ma. Yes, the 10 ( or 20ma ) is
current flow
Those ubiquitous motion detectors for outdoor lights use capacitive dropping
to supply the
low voltage for the ICs and electronics. Cap and small R in series with the
AC input to a bridge rectifier.
Works out well in that the bridge rectifier permits current flow in both
directions,
On 2015-Aug-23, at 9:54 AM, Steve Moulding wrote:
-Original Message-
From: cctalk [mailto:cctalk-boun...@classiccmp.org] On Behalf Of Brent
Hilpert
Sent: Sunday, August 23, 2015 3:07 AM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: RS-232 Tx / Rx monitoring LEDs
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: RS-232 Tx / Rx monitoring LEDs?
On 2015-Aug-22, at 11:55 PM, drlegendre . wrote:
On Sun, Aug 23, 2015 at 1:17 AM, Chuck Guzis ccl...@sydex.com wrote:
On 08/22/2015 10:23 PM, dwight wrote:
I would think the reverse voltage sum
On 08/22/2015 11:55 PM, drlegendre . wrote:
I've also seen C-R series voltage dropping circuits, here there.
Correct me if I'm wrong, but doesn't the series cap dissipate power
just as it would, were it a series resistor? I mean, if the LED is
passing 20mA, the cap is also doing 20mA - and at
On 08/23/2015 07:10 AM, dwight wrote:
I've used the capacitor method to provide most of the drop in the
past. I don't usually max out the LEDs at 20ma. I find there is
little difference between 10 and 20ma. Yes, the 10 ( or 20ma ) is
current flow through the capacitor. It is necessary to have
I've also seen C-R series voltage dropping circuits, here there.
Correct me if I'm wrong, but doesn't the series cap dissipate power just as
it would, were it a series resistor? I mean, if the LED is passing 20mA,
the cap is also doing 20mA - and at whatever the Vdrop is.
Right? If
On 2015-Aug-22, at 11:55 PM, drlegendre . wrote:
On Sun, Aug 23, 2015 at 1:17 AM, Chuck Guzis ccl...@sydex.com wrote:
On 08/22/2015 10:23 PM, dwight wrote:
I would think the reverse voltage sum of the diodes is enough.
Different diodes also can handle different voltages. Since the sum
of
On 08/22/2015 10:23 PM, dwight wrote:
I would think the reverse voltage sum of the diodes is enough.
Different diodes also can handle different voltages. Since the sum
of the forward voltages is enough to handle AC, I'd suspect the
reverse voltages each would handle is quite small as well.
The
From: ccl...@sydex.com
On 08/21/2015 08:36 AM, dwight wrote:
I was going to add something but it has already been said several
times. I will add that if using a LED on an AC like signal of high
voltage, one should use a diode. I recommend using a shunt diode
rather than a series diode
I was going to add something but it has already been
said several times.
I will add that if using a LED on an AC like signal of high voltage,
one should use a diode.
I recommend using a shunt diode rather than a series diode when
high voltages are being dropped by the resistor. It reduces the need
On Fri, Aug 21, 2015 at 8:36 AM, dwight dkel...@hotmail.com wrote:
I was going to add something but it has already been
said several times.
I will add that if using a LED on an AC like signal of high voltage,
one should use a diode.
I recommend using a shunt diode rather than a series diode
for a high voltage diode but makes the resistor hotter.
Some red LEDs glow orange when not protected from 12VAC.
I discovered (over 35 years ago) that green LEDs glow orange if massively
overcurrented (you know what I mean). No they don't last long like that. It
doesn't appear to be a thermal
On 08/21/2015 08:36 AM, dwight wrote:
I was going to add something but it has already been said several
times. I will add that if using a LED on an AC like signal of high
voltage, one should use a diode. I recommend using a shunt diode
rather than a series diode when high voltages are being
Totem pole outputs have comparable drive strength in both directions, that$
That's true for CMOS outputs. TTL outputs pull down much more strongly than$
Ok, but when you refer to drive strength I assumed you were talking about $
Maybe _rated_ current, but, even there, I don't think so (my TTL
A consideration with RS232 is that the signals swing to either side of 0, so$
It's been a while since I read the spec, but I think it's -3 to -20
volts one way and +3 to +20 the other, with the -3 to +3 range
deliberately left ambiguous. I think there are slew rate limits, too,
but I don't
On Thu, 8/20/15, Mouse mo...@rodents-montreal.org wrote:
Maybe _rated_ current, but, even there, I don't think so (my TTL
doc hasn't been unpacked yet, or I'd go check, but I'm fairly sure
they are generally specced to sink more current to GND
than source from Vcc).
It so happens I have a
On Aug 20, 2015, at 09:54 , Paul Koning paulkon...@comcast.net wrote:
Ok, but when you refer to drive strength I assumed you were talking about
current, not voltage. By that measure totem pole outputs are pretty much
symmetrical.
Again, CMOS totem pole outputs are pretty much
On Aug 19, 2015, at 11:40 PM, dwight dkel...@hotmail.com wrote:
I think the main issue is that TTL is usually a weak pullup and a hard
pulldown.
RS 232 levels are equal up and down.
That depends. Open collector outputs, yes, but those are the less common case.
Totem pole outputs have
On Thu, Aug 20, 2015 at 10:54 AM, Paul Koning paulkon...@comcast.net wrote:
Ok, but when you refer to drive strength I assumed you were talking about
current, not voltage. By that measure totem pole outputs are pretty much
symmetrical.
Not for true (bipolar) TTL. See the specs for the
On Aug 20, 2015, at 3:40 PM, Eric Smith space...@gmail.com wrote:
On Thu, Aug 20, 2015 at 10:54 AM, Paul Koning paulkon...@comcast.net wrote:
Ok, but when you refer to drive strength I assumed you were talking about
current, not voltage. By that measure totem pole outputs are pretty much
On Aug 20, 2015, at 11:58 AM, Mark J. Blair n...@nf6x.net wrote:
On Aug 20, 2015, at 06:27, Paul Koning paulkon...@comcast.net wrote:
Totem pole outputs have comparable drive strength in both directions, that's
precisely their purpose (to provide symmetric rise/fall times when driving
A consideration with RS232 is that the signals swing to either side of 0, so
if you use an LED
referenced to 0, it either needs a series diode or a sufficiently high
reverse voltage rating.
A diode in inverse parallel with the LED Is more normal when you want to run an
LED off
On Aug 20, 2015, at 06:27, Paul Koning paulkon...@comcast.net wrote:
Totem pole outputs have comparable drive strength in both directions, that's
precisely their purpose (to provide symmetric rise/fall times when driving
capacitive loads).
That's true for CMOS outputs. TTL outputs pull
are intended to account for this.
Usually the line is lower impedance than the input termination,
requiring the source to absorb the reflected signal.
This is why 422/485 came to be. The impedance of the loads better
match that of the termination.
Dwight
Subject: Re: RS-232 Tx / Rx monitoring LEDs
As part of my C-64 RS-232 to M15 60mA CL project, I've put together a
simple MAX232 based interface to connect the TTL levels on the C-64 to the
standard RS-232 +/- levels.
Is there any reason that I can or cannot install LEDs - on either side of
the MAX232 converter - to give some indication of
On 8/18/2015 10:40 PM, drlegendre . wrote:
As part of my C-64 RS-232 to M15 60mA CL project, I've put together a
simple MAX232 based interface to connect the TTL levels on the C-64 to the
standard RS-232 +/- levels.
Is there any reason that I can or cannot install LEDs - on either side of
the
Those little RS232 testers with LEDs built into a double DB25 connector box are
usually just made of LEDs and resistors connected to each signal line. They can
load signals enough to cause problems at high speeds, with weak drivers, or
with long cables, but usually they don't cause problems. If
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