Chip with simple program for Toy

In alt.engineering.electrical bud-- <remove.budnews@isp.com> wrote:
| phil-news-nospam@ipal.net wrote:
|> In alt.engineering.electrical Don Kelly <dhky@shaw.ca> wrote:
|>
|> | Now - is this all germane to household protection? You say not and I agree
|> | with you- because household equipment can ride through - at worst- doubling
|> | of the clamped voltage for a very short time even though the clamped voltage
|> | is relatively small compared to the peak of the incoming surge. --
|>
|> My belief is that they
|> can, and will at times.
|
| People believe in flying saucers.
| Where is a source that supports your belief?

My observations support my belief. I don't expect YOU to believe it on the
basis if MY observations, as I certainly won't believe things on the basis
of YOUR observations. What I am posting about is for you to UNDERSTAND what
I believe, not that you have to believe it. Maybe someday you will come to
understand it, and then you might realize how you have misread what it is
you have been quoting online.

Since you spend all your keystrokes making person attacks or insisting on
something being cited, or make quotes that are often truncated incorrectly
or misapplied, I can only conclude you have no actual understanding of what
it is you have been quoting. What good would me citing anything do for you
if you can't understand it.


|> I do agree that things can survive at the clamping voltage. But there has to
|> be a clamping situation. It's too easy for a surge to come in as a common
|> mode surge where the voltage difference across the MOVs would be (nearly) zero.
|> Then all we have is a propogating wavefront. And if it is strong and/or close
|> then we have very fast rise times. And it passes by the MOVs "laterally".
|
| Where is a source that supports your belief in nanosecond risetimes and
| 100MHz spectrum?

Another poster followed up to my post you just followed up to that also has
experienced the same thing. That might not be some published citation that
you want. But that doesn't matter. It seems you can't comprehend what this
is about regardless of whether it is observed by others, or yourself, or by
the experts you cite.


|> But one thing I do see in at least part of this thread is that Bud
|> focuses on quoting things other people say, and does very little to express
|> things in his own words.
|
| I focus on the real world. You focus on your beliefs.

You focus on citing and quoting things you do not understand well enough to
just talking about them in technical terms.


| Where is a source that supports your belief in nanosecond risetimes and
| 100MHz spectrum?

See above.

And after this round of followups, I'm done with this thread and with your
posts on this subject. You can have the last say, but I will not even read
it.

--
|WARNING: Due to extreme spam, I no longer see any articles originating from |
| Google Groups. If you want your postings to be seen by more readers |
| you will need to find a different place to post on Usenet. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

 

Mike Tomlinson <mike@jasper.org.uk> wrote:

... This is an important principle of the UK wiring code. It's
referred to as "equipotential bonding."

I wonder if "ring mains" (an extra wire from the last outlet to make
a loop back to the fusebox) are legal in the US. Seems like a nice way
to improve voltage regulation with a little extra wire, and if the ring
wire only breaks in one place, all the outlets keep working.

Nick

 

Mike Tomlinson <mike@jasper.org.uk> wrote:

... This is an important principle of the UK wiring code. It's
referred to as "equipotential bonding."

I wonder if "ring mains" (an extra wire from the last outlet to make
a loop back to the fusebox) are legal in the US. Seems like a nice way
to improve voltage regulation with a little extra wire, and if the ring
wire only breaks in one place, all the outlets keep working.

Nick

 

In alt.engineering.electrical nicksanspam@ece.villanova.edu wrote:

| Mike Tomlinson <mike@jasper.org.uk> wrote:
|
|>... This is an important principle of the UK wiring code. It's
|>referred to as "equipotential bonding."
|
| I wonder if "ring mains" (an extra wire from the last outlet to make
| a loop back to the fusebox) are legal in the US. Seems like a nice way
| to improve voltage regulation with a little extra wire, and if the ring
| wire only breaks in one place, all the outlets keep working.

It is not legal in the US. It is also considered technically unsafe.

You could wire a ring circuit with AWG #14 CU rated at 15 amps and protect
it with a 30 amp breaker under the theory that the current would be split
across the 2 paths between the source (breaker) and the load. This is the
most unsafe configuration because if one of the wires breaks, the breaker
will not detect it, and you won't notice until a fire starts.

You could wire the same circuit to two separate 15 amps breakers. In this
case it is somewhat safer because if one wire breaks, you can't get any use
via one of the breakers, effectivly reducing the current that would trip
the circuit via the remaining breaker. This is still unsafe because the
broken wire could merely be loose, and shutting off one breaker would leave
the circuit potentially live via the other breaker as the wire could come
back in contact.

There could also be confusion with separate breakers. The breakers have to
be on the same pole (phase), an issue not present in the single pole single
phase home wiring most homes have in UK. The USA, however, has two pole
single phase wiring. One way around that would be a "tandem" breaker with
the two handles fused together.

The safest case would be wiring both ends of the ring into the same breaker
rated for the current capacity of the wire as if used in a regular branch
circuit. Even this would have a safety issue. If the wire became loose at
one point in the ring, it would still be a potential hot spot that would be
not as easily noticed as a similar loose wire in a branch circuit. That hot
spot could then start a fire.

So far I have only described issues with the hot wiring. There are issues
with the neutral wiring as well. In all the above configurations, a neutral
would have to be wired in from both ends of the ring, and each be wired in
a separate hole (not doubled up) in the neutral bus bar. A loose neutral in
all these cases would go unnoticed just like a hot wire. But in cases where
the total current available (either the 30 amp single breaker, or tandem 15
amp breakers, described above) exceeds the wiring (when neutral is AWG #14 CU)
a wiring overheating problem exists.

The grounding wire would also have to be wired correctly from both ends.

An even greater double hazard potential exists when the neutral on one end is
broken while the hot on the other end is broken (or shut off at the breaker).
This creates a large inductive loop which can energize other wiring and cause
various problems with many metallic constructions.

Very little is gained by doing this over direct branch circuits. The issue
of voltage stability is addressed by keeping branch circuits short. It is
my understanding that UK ring circuits tend to be longer and run all around
the portion of a house (often an entire floor). Branch circuits in the USA
tend to be shorter.

Very long circuits can have voltage issues. An example is a home with a 1000
foot long driveway into the property, and a string of many lights along the
way. The more distant lights would be dimmer. This can be addressed to at
least balance out the dimming by using a loop-back circuit, which is still a
branch circuit. This is a more expensive circuit that is done by having an
extra hot wire run with the circuit in the same cable or conduit. Each lamp
is connected between the extra wire and the neutral. The extra wire is then
connected to the fed hot wire at the last lamp in the string. There is no
other connected to the fed hot wire other than the last lamp and the source
controlling switch. With this loop-back circuit, each lamp has the same
circuit length, and thus will have the same voltage drop.

The above technique was discussed on electrical-contrator.net a while back,
but they have since changed web site software, and my old links do not work.

--
|WARNING: Due to extreme spam, I no longer see any articles originating from |
| Google Groups. If you want your postings to be seen by more readers |
| you will need to find a different place to post on Usenet. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

 

In alt.engineering.electrical VWWall <vwall@large.invalid> wrote:

| I had a microwave oven that had a MOV across the 120V line ahead of the
| power switch. The other side of the 120/240 20A circuit supplied a
| refrigerator. The loss of the neutral applied a good part of the 240V
| across the MOV when the refrigerator attempted to start.
|
| The MOV didn't last long! It would probably have been OK on the load
| side of the switch.
|
| I know that refrigerators should be alone on a "home run" circuit, and
| neutrals shouldn't be connected with wire nuts, but that wasn't how it was!

How would you connect a neutral? Doubled up on a receptacle device screw?
The usual practice is to wire the neutral in a wire nut so it can feed the
device in that box, as well as connect up and down stream, even if the
device is removed.

OTOH, I don't like wire nuts. I've seen them come loose even when wired
together well. Maybe it was a defective nut. I definitely will try to
avoid them when my new house gets built (a lot of bad electrical things
will be avoided in it).


| My only complaint with some plug-in protectors is that the MOVs are
| often much too small. I've also seen some with only a line-line MOV.

You had a plug-in protector for a double line (240V) circuit? Or are you just
referring to the neutral as one of the lines?

I'm still on the hunt for a plug-in surge suppressor power strip for 240V
with NEMA 6-15P plug and NEMA 6-15R outlets. The MOVs between each line
and ground need to be the ones appropriate for 120V (330V clamp rated) and
the ones between the two lines appropriate for 240V (660V clamp rated).

--
|WARNING: Due to extreme spam, I no longer see any articles originating from |
| Google Groups. If you want your postings to be seen by more readers |
| you will need to find a different place to post on Usenet. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

 

In alt.engineering.electrical Eric <me@nomail.com> wrote:
| phil-news-nospam@ipal.net wrote:
|> In alt.engineering.electrical Eric <me@nomail.com> wrote:
|>
|> | I can attest to vhf/uhf content in lightning strikes. I worked for a
|> | communications outfit. We owned and maintained a number of comm sites
|> | with towers and antennas. One strike on an antenna destroyed the LDF rf
|> | cable all the way to the polyphaser at the bottom of the tower. It had
|> | blowouts at about 1 foot intervals all down it's length suggesting a
|> | 1/2 wave of about 1 foot or approx 460 mhz. That's one hell of a lot of
|> | energy at that frequency..
|>
|> Apparently you had some kind of resonance involved. Maybe the antenna itself
|> can cause that. Or the output tank circuit in the transmitter. Once you have
|> the resonance to narrowband the energy, it would only take a reflection back
|> up the line and you turn a propogating surge into standing waves.
|>
| Pretty much what we determined. Also in another thread I stressed that
| the rise time by itself does not determine frequency content. One needs
| to know the rate of change, or slew rate, to determine that. A
| lightning pulse may have a rise time of 1.2 microseconds but in that
| short time the current can rise to thousands of amps, generating a large
| amount of vhf,uhf energy.

In some plots of voltage rises I've seen in the past, the rise was not at all
a smooth one. It went up in steps. Of course if one _thinks_ there will be
no VHF or UHF energy and does measurement with a ssytem only capable of lower
frequencies, that would smooth out how the rise appears.

--
|WARNING: Due to extreme spam, I no longer see any articles originating from |
| Google Groups. If you want your postings to be seen by more readers |
| you will need to find a different place to post on Usenet. |
| Phil Howard KA9WGN (email for humans: first name in lower case at ipal.net) |

 

[Paul E. Schoen]

"John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote in message
news:fequ141vjhdqon40lhh23ms22rilda2hjk@4ax.com...

On Sun, 04 May 2008 16:18:44 -0700, "Fritz Oppliger"
fritz@fritzop.dot.com> wrote:

On Sun, 04 May 2008 14:23:56 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:


Brushless DC fans draw spikey current and locally make AC magnetic
fields. Both are low frequency, numbers roughly like 80 Hz. The
current ripple can get into power supplies and bother low-level analog
circuits, and may cause ground loop noise. The mag fields can induce
low-level (microvolts, typically) voltages into loops on nearby
circuit boards.

What is your "measurement device"?

OK don't laugh -
(C) 1995 Connectware PCboard with 10 LEDs on it. It has a 43mm square
antenna loop area (in to 18 mm at the center)
it sports an LM 3914V and a TLE2114C IC. Powered by 9V battery, purchased
from BG Micro about ten years ago. It lights up all the LEDs when I get
to
within 3 inches of the fans, tapering off to zero within 10 inches from
the fans.
It WAS sold as EMF detector. It seems to work as such. It is what I have.
It is quite sensitive, a fraction of an inch makes a big difference in
the
display.

** Posted from http://www.teranews.com **



Why are you "tasked" to satisfy what is probably a crap, uncalibrated
instrument?

The example of heart rate variability in newborns in incubators may be
caused by 50-60 Hz EM fields, which is a dangerous frequency that can cause
fibrillation (but usually because of conducted current through heart
muscle). If your instrument shows zero levels at 10" from the fans, then
why not maintain that distance? Also, see if there is a problem if you run
the fan on a smooth DC signal. You can filter the PWM if that is the cause
of the noise. And if your project is as sensitive and important as
protecting infants in incubators, you really need to invest in some
accurate and reliable equipment, and you probably should get data on the
field strength that was measured in the experiments you cited in the
article.

A simple magnetic field sensor can be made from an air core choke, and can
be connected to a scope to see the frequency and intensity. The choke's
axis can be oriented to determine the direction of the field. This will
probably be more useful than your unknown instrument. You can probably
produce a known field strength by passing a measured current through a
toroidal transformer and placing the sensor in the hole.

Paul

 

w_tom <w_tom1@usa.net> wrote:

What will provide sufficient earthing?

A large series air-core copper toroid (eg 1' diam x 2' long with
a 3" wire spacing) followed by a small spark gap to a poor ground.

Nick

 

<phil-news-nospam@ipal.net> wrote:

nicksanspam@ece.villanova.edu wrote:

| I wonder if "ring mains" (an extra wire from the last outlet to make
| a loop back to the fusebox) are legal in the US. Seems like a nice way
| to improve voltage regulation with a little extra wire, and if the ring
| wire only breaks in one place, all the outlets keep working.

It is not legal in the US. It is also considered technically unsafe.

Lots of things are "technically unsafe" Safety is often used as excuse
for people-control...

The safest case would be wiring both ends of the ring into the same breaker
rated for the current capacity of the wire as if used in a regular branch
circuit.

Sounds good to me.

... If the wire became loose at one point in the ring, it would still be
a potential hot spot

Maybe not too hot, if the rest of the wire is intact.

... a neutral would have to be wired in from both ends of the ring, and
each be wired in a separate hole (not doubled up) in the neutral bus bar.

The "separate hole problem" has lots of solutions.

... The issue of voltage stability is addressed by keeping branch circuits
short. It is my understanding that UK ring circuits tend to be longer and
run all around the portion of a house (often an entire floor).

Sounds more cost-effective to me. Why don't more people use large PEX pipe
"ring mains" with Ts, vs home runs with tiny pipe and expensive manifolds?

Nick

 

[charles]

In article <76535$4821baa0$4213eb20$7766@DIALUPUSA.NET>,
bud-- <remove.budnews@isp.com> wrote:

Mike Tomlinson wrote:
In article <8fa76$482087fc$4213ea45$31115@DIALUPUSA.NET>, bud--
remove.budnews@isp.com> writes

Last I heard UK phone entry protectors did not clamp the voltage to
earth.

You're quite correct. It's a practice that the GPO (forerunner to
British Telecom) abandoned in the 1960s, showing how up to date w_'s
"knowledge" is.


Phone wires were clamped to ground before the 1960s?

not as such, but phones in rural areas often had an earth terminal on the
household terminal box.

--
From KT24 - in "Leafy Surrey"

Using a RISC OS computer running v5.11

 

[Tantalust]

"w_tom" <w_tom1@usa.net> wrote in message
news:b224d456-f25c-4c73-bfe5-c546c7871592@e53g2000hsa.googlegroups.com...

On May 6, 2:45 pm, Sjouke Burry <burrynulnulf...@ppllaanneett.nnlll
wrote:
Can you trim W_tom with that?? Or is he incurable?

He is incurable as long as others post outright lies and myths while
denying what really provides surge protection. Now to discuss what is
relevant.

What's becoming more relevant here every day is your mental illness. . . . .
along with your terrible OCD disadvantage, constantly referring to yourself
in the third-person is pointing to a flourishing
Depersonalization/Dissociative Identity Disorder. You can look it up.

 

[Tantalust]

"w_tom" <w_tom1@usa.net> wrote in message
news:b224d456-f25c-4c73-bfe5-c546c7871592@e53g2000hsa.googlegroups.com...

On May 6, 2:45 pm, Sjouke Burry <burrynulnulf...@ppllaanneett.nnlll
wrote:
Can you trim W_tom with that?? Or is he incurable?

He is incurable as long as others post outright lies and myths while
denying what really provides surge protection. Now to discuss what is
relevant.

What's becoming more relevant here every day is your mental illness. . . . .
along with your terrible OCD disadvantage, constantly referring to yourself
in the third-person is pointing to a flourishing
Depersonalization/Dissociative Identity Disorder. You can look it up.

 

[Phil Allison]

"RichDickead "
"Phil Allison"

I purchased an armband radio recently, for jogging.
Truetech, if that means anything.

I inserted 2 new alkaline AAA batteries, they
are now dead after about 90 minutes use.
Is that normal?

** What does the maker's spec sheet say ?
Have you ask the dealer what is the normal running time?

Ask the dealer, good one, Philster,
hahaha!!! It's Target - staffed by highly
trained audio electronics professionals!

** No expertise is needed to say how long something runs on set of
tteries - fuckhead.

You dumb question is more suited to some
consumer whinger's forum.

I figured this group includes some
experienced circuit designers, who
might estimate the expected power
burn on a portable FM radio.

** Totally irrelevant to your problem - fuckhead.

But please, direct me to one of these
whinger's forums,

** Use Google - you asshole.



...... Phil

 

w_tom <w_tom1@usa.net> wrote:

Also required for UL approval is total number of joules. That says
nothing about how many joules actually participate in protection.
Typically, plug-in protectors use as little as 1/3rd and never more
than 2/3rd of its joules for protection.

How does a protector decide how many of its joules to use?

Nick

 

w_tom <w_tom1@usa.net> wrote:

... Surge protection without that short connection to earth ground
is *ineffective*.

Wrong, wrong, wrong (say it 3 times and it's true

Nick, ex-K3VZW, BSEE, MSEE, Senior Member, IEEE

 

[Phil Allison]

"sparky" <sparky12x@yahoo.com>



** Go drop dead -

you vile autistic, ADHD fucked pile of dog shit.

 

[Dan Coby]

"ehsjr" <e.h.s.j.r.removethespampunctuation@bellatlantic.net> wrote in message
news:cxHUj.28009$zw.4986@trnddc04...

vic wrote:
Hi,

I have two common anode 7-segments displays, and only one wire to drive them. I need to achieve
the following : when the control signal is +5V, display1 is ON and display2 is OFF. When the
signal is 0V, display1 is OFF and display2 is ON. When the signal is not connected (high
impedance), both displays are OFF.

I tried using a NPN transistor for display1 and a PNP for display2, connecting their bases
together. It works when the driving signal is present, but when the signal is floating current
flows from the base of the PNP to the base of the NPN and both transistors turn each other on,
resulting in both displays being ON.

The circuit that didn't work :

VCC
+
|
|
___ |
o---------------------|___|--|
| |\
| VCC |
| + |
| | Display2
| | |
| ___ |/ |
Input---o---|___|--| GND
|
|
|
Display1
|
|
GND



Is there a way to achieve this ?

Thanks.

Add diodes to isolate the bases, and resistors
to bias the transistors off when the desired
on signal is not present.

Ed

see below



VCC
+
|
+-------------+
| |
[R] |
| ___ |
o--------|<------+----|___|--|
| |\
| VCC |
| + |
| | Display2
| | |
| ___ |/ |
Input---o--->|-+-|___|--| GND
| |
[R] |
| |
| Display1
| |
+----------+
|
GND

The revised circuit does not solve the problem. Both diodes
will be conducting when the input is floating. As a result both
displays will still be on.

A simpler solution is to remove the diodes, change the
locations of the added resistors, and move Display1. I.e.:

VCC
+
|
+---------+
| |
[R1] |
| |<
o-------------[R2]---+-------|
| |\
| VCC |
| + |
| | Display2
| Display1 |
| | |
| |/ |
Input---o-----[R2]-+--------| GND
| |>
[R1] |
| |
+----------+
|
GND

The R1 / R2 resistor pairs need to be chosen so that
there is only about 0.5 volts across the transistors'
base-emitter junctions when the input is floating.
When the input is floating, the various resistors
will pull the input to VCC/2. The value of 0.5 volts was
chosen to be low enough to keep the transistors from
turning on when the input is floating but still allow the
transistors to be turned on when the input is being driven
to VCC or ground.

 

[petrus bitbyter]

"vic" <news@bidouille.org> schreef in bericht
news:48233453$0$20289$426a74cc@news.free.fr...

Hi,

I have two common anode 7-segments displays, and only one wire to drive
them. I need to achieve the following : when the control signal is +5V,
display1 is ON and display2 is OFF. When the signal is 0V, display1 is OFF
and display2 is ON. When the signal is not connected (high impedance),
both displays are OFF.

I tried using a NPN transistor for display1 and a PNP for display2,
connecting their bases together. It works when the driving signal is
present, but when the signal is floating current flows from the base of
the PNP to the base of the NPN and both transistors turn each other on,
resulting in both displays being ON.

The circuit that didn't work :

VCC
+
|
|
___ |
o---------------------|___|--|
| |\
| VCC |
| + |
| | Display2
| | |
| ___ |/ |
Input---o---|___|--| GND
|
|
|
Display1
|
|
GND



Is there a way to achieve this ?

Thanks.

Try this circuit. Choose the resistor values to limit the base current into
the transistors, yet this current should be high enough to drive the
transistors into saturation.

+--------+------------------+-------+--Vcc
| | | |
___ |< | | .---.
in----+--|___|---| | | | |
| |\ | .-. | D |
| | | | | | |
| | |< | | '---'
| +------| '-' |
| | |\ | |/
| .-. | +-----|
| | | .---. | |>
| | | | | | |
| '-' | D | ___ |/ |
| | | | +-|___|---| |
| | '---' | |> |
| | | | | |
------)------------+--------+------)-----------+-------+--GND
| |
+----------------------------+


If your displays need GND on one side, then try this. Mind the type of the
transistors.

+--------+------------------+-------+--Vcc
| | | |
___ |< | ___ |/ |
in----+--|___|---| | +--|___|--| |
| |\ | | |> |
| | | | | |
| | |< | | |<
| +------| | +-----|
| | |\ | | |\
| .-. | | .-. |
| | | .---. | | | .---.
| | | | | | | | | |
| '-' | D | | '-' | D |
| | | | | | | |
| | '---' | | '---'
| | | | | |
------)------------+--------+------)-----------+-------+--GND
| |
+----------------------------+
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

petrus bitbyter

 

[petrus bitbyter]

"Dan Coby" <adcoby@earthlink.net> schreef in bericht
news:7vCdnV2xQMRN4b7VnZ2dnUVZ_oqhnZ2d@earthlink.com...

"ehsjr" <e.h.s.j.r.removethespampunctuation@bellatlantic.net> wrote in
message news:cxHUj.28009$zw.4986@trnddc04...
vic wrote:
Hi,

I have two common anode 7-segments displays, and only one wire to drive
them. I need to achieve the following : when the control signal is +5V,
display1 is ON and display2 is OFF. When the signal is 0V, display1 is
OFF and display2 is ON. When the signal is not connected (high
impedance), both displays are OFF.

I tried using a NPN transistor for display1 and a PNP for display2,
connecting their bases together. It works when the driving signal is
present, but when the signal is floating current flows from the base of
the PNP to the base of the NPN and both transistors turn each other on,
resulting in both displays being ON.

The circuit that didn't work :

VCC
+
|
|
___ |
o---------------------|___|--|
| |\
| VCC |
| + |
| | Display2
| | |
| ___ |/ |
Input---o---|___|--| GND
|
|
|
Display1
|
|
GND



Is there a way to achieve this ?

Thanks.

Add diodes to isolate the bases, and resistors
to bias the transistors off when the desired
on signal is not present.

Ed

see below



VCC
+
|
+-------------+
| |
[R] |
| ___ |
o--------|<------+----|___|--|
| |\
| VCC |
| + |
| | Display2
| | |
| ___ |/ |
Input---o--->|-+-|___|--| GND
| |
[R] |
| |
| Display1
| |
+----------+
|
GND

The revised circuit does not solve the problem. Both diodes
will be conducting when the input is floating. As a result both
displays will still be on.

A simpler solution is to remove the diodes, change the
locations of the added resistors, and move Display1. I.e.:

VCC
+
|
+---------+
| |
[R1] |
| |
o-------------[R2]---+-------|
| |\
| VCC |
| + |
| | Display2
| Display1 |
| | |
| |/ |
Input---o-----[R2]-+--------| GND
| |
[R1] |
| |
+----------+
|
GND

The R1 / R2 resistor pairs need to be chosen so that
there is only about 0.5 volts across the transistors'
base-emitter junctions when the input is floating.
When the input is floating, the various resistors
will pull the input to VCC/2. The value of 0.5 volts was
chosen to be low enough to keep the transistors from
turning on when the input is floating but still allow the
transistors to be turned on when the input is being driven
to VCC or ground.

This may work, (so there are some ifs.)
Most important, the driving source must be able to provide the extra current
(sink and source).
The displays may need GND on one side. The OP did not said so, but his
schematic suggests it.
You need to do a little bit of serious calculation to find the values of the
resistors. The voltages are important as you mentioned already, but the base
currents need to be high enough to switch the transistors on when active. I
leave it an excercise for the interested reader.

petrus bitbyter

 

[BobW]

"vic" <news@bidouille.org> wrote in message
news:48233453$0$20289$426a74cc@news.free.fr...

Hi,

I have two common anode 7-segments displays, and only one wire to drive
them. I need to achieve the following : when the control signal is +5V,
display1 is ON and display2 is OFF. When the signal is 0V, display1 is OFF
and display2 is ON. When the signal is not connected (high impedance),
both displays are OFF.

I tried using a NPN transistor for display1 and a PNP for display2,
connecting their bases together. It works when the driving signal is
present, but when the signal is floating current flows from the base of
the PNP to the base of the NPN and both transistors turn each other on,
resulting in both displays being ON.

The circuit that didn't work :

VCC
+
|
|
___ |
o---------------------|___|--|
| |\
| VCC |
| + |
| | Display2
| | |
| ___ |/ |
Input---o---|___|--| GND
|
|
|
Display1
|
|
GND



Is there a way to achieve this ?

Thanks.

Try this:
5V
| 5V
R5 |
| |<---
|/-------------| Q3
----| Q1 |\--------- (to display 1 and then to GND)
| |>-- 5V
| | |
| | R3
| | |
---R1-----R2----------
| | |
| | R4
| |<--- |
|--| Q2 GND
|\
| |/--------- (to display 2 and then to 5V)
-------------| Q4
| |>----
R6 |
| GND
GND

Q1 and Q2 form a comparator so that when the input is floating they will
both be off. R3 and R4 set the input threshold.

When the input is high (5V) then Q1 will be on and that will turn on Q3.
When the input is low (GND) then Q2 will be on and that will turn on Q4.

You can figure out the resistor values. They shouldn't be too critical, but
R3 and R4 need to be small enough to ensure enough drive for the four
transistors.

I hope I got the ascii art right as I had to compose it in a separate word
processor.

Bob
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