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.

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

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.

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.

"ehsjr" <e.h.s.j.r.removethespampunctuation at (no spam) bellatlantic.net> wrote in
message news:cxHUj.28009$zw.4986 at (no spam) 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.

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.

"vic" <news at (no spam) bidouille.org> wrote in message
news:48233453$0$20289$426a74cc at (no spam) 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
--
== NOTE: I automatically delete all Google Group posts due to uncontrolled
SPAM ==

"Dan Coby" <adcoby at (no spam) earthlink.net> schreef in bericht
news:7vCdnV2xQMRN4b7VnZ2dnUVZ_oqhnZ2d at (no spam) earthlink.com...
"ehsjr" <e.h.s.j.r.removethespampunctuation at (no spam) bellatlantic.net> wrote in message
news:cxHUj.28009$zw.4986 at (no spam) 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.

"ehsjr" <e.h.s.j.r.removethespampunctuation at (no spam) bellatlantic.net> wrote in message
news:cxHUj.28009$zw.4986 at (no spam) 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.

The displays may need GND on one side. The OP did not said so, but his
schematic suggests it.

"BobW" <nimby_NEEDSPAM at (no spam) roadrunner.com> wrote in message
news:B7mdnSJSKb17P77VnZ2dnUVZ_obinZ2d at (no spam) giganews.com...
"vic" <news at (no spam) bidouille.org> wrote in message
news:48233453$0$20289$426a74cc at (no spam) 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
--
== NOTE: I automatically delete all Google Group posts due to uncontrolled
SPAM ==

I see, now, that your displays are both common anode. You'll need to add
another PNP (common emitter mode) driven by Q4.

As Monica Lewinsky used to say, "Close, but no cigar."

Bob

"ehsjr" <e.h.s.j.r.removethespampunctuation at (no spam) bellatlantic.net> wrote in message
news:cxHUj.28009$zw.4986 at (no spam) 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.

BobW wrote:
"BobW" <nimby_NEEDSPAM at (no spam) roadrunner.com> wrote in message
news:B7mdnSJSKb17P77VnZ2dnUVZ_obinZ2d at (no spam) giganews.com...
"vic" <news at (no spam) bidouille.org> wrote in message
news:48233453$0$20289$426a74cc at (no spam) 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
--
== NOTE: I automatically delete all Google Group posts due to
uncontrolled SPAM ==

I see, now, that your displays are both common anode. You'll need to add
another PNP (common emitter mode) driven by Q4.

As Monica Lewinsky used to say, "Close, but no cigar."

Bob

*gasp* 5 transistors needed to do what seemed simple at first glance ...

I don't quite understand what R5 and R6 are for, when Q1 and Q2 do not
conduct, the base current of Q3 and Q4 would be zero so the ressitors do
not seem necessary ?

Well I guess I could just try it and see if it works

"vic" <news at (no spam) bidouille.org> schreef in bericht
news:48250145$0$5055$426a74cc at (no spam) news.free.fr...
BobW wrote:
"BobW" <nimby_NEEDSPAM at (no spam) roadrunner.com> wrote in message
news:B7mdnSJSKb17P77VnZ2dnUVZ_obinZ2d at (no spam) giganews.com...
"vic" <news at (no spam) bidouille.org> wrote in message
news:48233453$0$20289$426a74cc at (no spam) 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
--
== NOTE: I automatically delete all Google Group posts due to
uncontrolled SPAM ==

I see, now, that your displays are both common anode. You'll need to add
another PNP (common emitter mode) driven by Q4.

As Monica Lewinsky used to say, "Close, but no cigar."

Bob

*gasp* 5 transistors needed to do what seemed simple at first glance ...

I don't quite understand what R5 and R6 are for, when Q1 and Q2 do not
conduct, the base current of Q3 and Q4 would be zero so the ressitors do
not seem necessary ?

Well I guess I could just try it and see if it works :)


Didn't you see my four transistors, four resistors solution yesterday?

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


petrus bitbyter