Attached is the schematic of the circuit I am working on, which is basically
a 555 timer running (IIRC) as a multivibrator, clocking the 4027 chip
mentioned, which drives a simple transistor tester with Q1 and not-Q1, and
alternating the configuration of the tester with Q2. This is the basic
model, which I am trying to get working so I can expand it. Frustration is,
I had it working at one time, but can't remember what I changed that made it
stop working. It was constructed as shown on a breadboard but got shoved up
under the bed for a while due to more pressing concerns. I am trying to
dust it off, and pick it up again. Any help would be greatly appreciated.

OPERATION is supposed to be as follows: Q1 and not-Q1 alternately bias the
transistor pluged into the E/B/C sockets as a PNP or NPN device, indicating
which polarity the device is by illuminating one of the two LEDs in the
schematic. When the transistor successfully turns on, it shorts out one of
the two LEDs, so that one LED flashing indicates the polarity of the device
under test. Two LEDs flashing mean no transistor, or one that will not
conduct when biased appropriately. Neither LED flashing indicates a shorted
transistor. And yes, it does work. PROBLEM arises when I try to use the
74HC4053 in the lower left corner to change the configuraton of the E/B/C
sockets for a transistor with E/C/B pin configuration (like an NTE199)
rather than standard E/B/C pin configuration (like a 2N3904 or 2N3906). To
make this happen, I use Q2 to alternately send the "Select A/B/C" pins of
the 74HC4053 high and low, which alters which of the a/b/c (lowercase) pins
are connected to the A/B/C (uppercase) input/output pins that are in turn
connected to the E/BC sockets of the basic tester. And, yes, I can make
this happen too. But not with the shown schematic. To make this last part
happen, I must disconnect Q2 from the Select A/B/C pins, and connect not-Q2.
With this change the project tells me that the NTE199 under test is
functional as an NPN transistor. But it will not tell me anything about the
2N3904 or the 2N3906. To re-establish that functionality, I must disconnect
not-Q2 and reconnect Q2 to the Select A/B/C pins of the 74HC4053. And this,
if I am not mistaken, is *not* the way it is supposed to work. If I am to
understand correctly, Q2 going from high to low (logic 1 to logic 0?) should
do it all. Someone please enlighten me. What am I missing?

Ignorantly yours...

Dave

PS: For whatever mistakes I have made in my description of the circuit or
its operation, I can only ask patience. I am not a degreed individual
(nobody was wondering about that, right?) and I do not have any cookbooks
under my belt. I am merely a tinkerer trying to produce something
worthwhile. As I said before, any help is greatly appreciated.

"Dave" wrote in message
netamerica...
Attached is the schematic of the circuit I am working on, which is
basically a 555 timer running (IIRC) as a multivibrator, clocking the 4027
chip mentioned, which drives a simple transistor tester with Q1 and
not-Q1, and alternating the configuration of the tester with Q2. This is
the basic model, which I am trying to get working so I can expand it.
Frustration is, I had it working at one time, but can't remember what I
changed that made it stop working. It was constructed as shown on a
breadboard but got shoved up under the bed for a while due to more
pressing concerns. I am trying to dust it off, and pick it up again. Any
help would be greatly appreciated.

OPERATION is supposed to be as follows: Q1 and not-Q1 alternately bias the
transistor pluged into the E/B/C sockets as a PNP or NPN device,
indicating which polarity the device is by illuminating one of the two
LEDs in the schematic. When the transistor successfully turns on, it
shorts out one of the two LEDs, so that one LED flashing indicates the
polarity of the device under test. Two LEDs flashing mean no transistor,
or one that will not conduct when biased appropriately. Neither LED
flashing indicates a shorted transistor. And yes, it does work. PROBLEM
arises when I try to use the 74HC4053 in the lower left corner to change
the configuraton of the E/B/C sockets for a transistor with E/C/B pin
configuration (like an NTE199) rather than standard E/B/C pin
configuration (like a 2N3904 or 2N3906). To make this happen, I use Q2 to
alternately send the "Select A/B/C" pins of the 74HC4053 high and low,
which alters which of the a/b/c (lowercase) pins are connected to the
A/B/C (uppercase) input/output pins that are in turn connected to the E/BC
sockets of the basic tester. And, yes, I can make this happen too. But
not with the shown schematic. To make this last part happen, I must
disconnect Q2 from the Select A/B/C pins, and connect not-Q2. With this
change the project tells me that the NTE199 under test is functional as an
NPN transistor. But it will not tell me anything about the 2N3904 or the
2N3906. To re-establish that functionality, I must disconnect not-Q2 and
reconnect Q2 to the Select A/B/C pins of the 74HC4053. And this, if I am
not mistaken, is *not* the way it is supposed to work. If I am to
understand correctly, Q2 going from high to low (logic 1 to logic 0?)
should do it all. Someone please enlighten me. What am I missing?

Ignorantly yours...

Dave

PS: For whatever mistakes I have made in my description of the circuit or
its operation, I can only ask patience. I am not a degreed individual
(nobody was wondering about that, right?) and I do not have any cookbooks
under my belt. I am merely a tinkerer trying to produce something
worthwhile. As I said before, any help is greatly appreciated.





A couple of observations-
The 555 used as an oscillator has a notorious glitch on the pin 3 output.
There are ways of dealing with this like putting a .01uF from pin 3 to gnd.
The other way is to disconnect R2 from pin 7 and take it instead to pin 3.
You can then take your output from pin 7. Pin 7 is the discharge pin but it
makes an equally good open collector drive. Since you have R1 as a pullup on
this pin, you're good to go. Using pin 3 to drive the RC works since it is a
totem pole drive. The frequency and pulsewidth will be a bit different but
frequency is now set with one resistor...

Breadboards (protoboard) are very handy to use for trying things out but
awful for spurrious coupling. The rows of pins are separated from adjacent
rows by a thin spacer and make for capacitive coupling. This can really mess
up clocked devices. When in doubt, use a few hundred pF from the clock line
to gnd to test if it makes the problem go away.

See if this gets you going and then you can futz with the 4053.

Oppie
(been there, did that, bought the tee shirt)

"Oppie" wrote in message
...

"Dave" wrote in message
netamerica...
Attached is the schematic of the circuit I am working on, which is
basically a 555 timer running (IIRC) as a multivibrator, clocking the
4027 chip mentioned, which drives a simple transistor tester with Q1 and
not-Q1, and alternating the configuration of the tester with Q2. This is
the basic model, which I am trying to get working so I can expand it.
Frustration is, I had it working at one time, but can't remember what I
changed that made it stop working. It was constructed as shown on a
breadboard but got shoved up under the bed for a while due to more
pressing concerns. I am trying to dust it off, and pick it up again.
Any help would be greatly appreciated.

OPERATION is supposed to be as follows: Q1 and not-Q1 alternately bias
the transistor pluged into the E/B/C sockets as a PNP or NPN device,
indicating which polarity the device is by illuminating one of the two
LEDs in the schematic. When the transistor successfully turns on, it
shorts out one of the two LEDs, so that one LED flashing indicates the
polarity of the device under test. Two LEDs flashing mean no transistor,
or one that will not conduct when biased appropriately. Neither LED
flashing indicates a shorted transistor. And yes, it does work. PROBLEM
arises when I try to use the 74HC4053 in the lower left corner to change
the configuraton of the E/B/C sockets for a transistor with E/C/B pin
configuration (like an NTE199) rather than standard E/B/C pin
configuration (like a 2N3904 or 2N3906). To make this happen, I use Q2
to alternately send the "Select A/B/C" pins of the 74HC4053 high and low,
which alters which of the a/b/c (lowercase) pins are connected to the
A/B/C (uppercase) input/output pins that are in turn connected to the
E/BC sockets of the basic tester. And, yes, I can make this happen too.
But not with the shown schematic. To make this last part happen, I must
disconnect Q2 from the Select A/B/C pins, and connect not-Q2. With this
change the project tells me that the NTE199 under test is functional as
an NPN transistor. But it will not tell me anything about the 2N3904 or
the 2N3906. To re-establish that functionality, I must disconnect not-Q2
and reconnect Q2 to the Select A/B/C pins of the 74HC4053. And this, if
I am not mistaken, is *not* the way it is supposed to work. If I am to
understand correctly, Q2 going from high to low (logic 1 to logic 0?)
should do it all. Someone please enlighten me. What am I missing?

Ignorantly yours...

Dave

PS: For whatever mistakes I have made in my description of the circuit or
its operation, I can only ask patience. I am not a degreed individual
(nobody was wondering about that, right?) and I do not have any cookbooks
under my belt. I am merely a tinkerer trying to produce something
worthwhile. As I said before, any help is greatly appreciated.





A couple of observations-
The 555 used as an oscillator has a notorious glitch on the pin 3 output.
There are ways of dealing with this like putting a .01uF from pin 3 to
gnd. The other way is to disconnect R2 from pin 7 and take it instead to
pin 3. You can then take your output from pin 7. Pin 7 is the discharge
pin but it makes an equally good open collector drive. Since you have R1
as a pullup on this pin, you're good to go. Using pin 3 to drive the RC
works since it is a totem pole drive. The frequency and pulsewidth will be
a bit different but frequency is now set with one resistor...

Breadboards (protoboard) are very handy to use for trying things out but
awful for spurrious coupling. The rows of pins are separated from adjacent
rows by a thin spacer and make for capacitive coupling. This can really
mess up clocked devices. When in doubt, use a few hundred pF from the
clock line to gnd to test if it makes the problem go away.

See if this gets you going and then you can futz with the 4053.

Oppie
(been there, did that, bought the tee shirt)




Cool. Thank you for this, Oppie. Will definetly try it out. Very much
appreciated...

Dave

"Oppie" wrote in message
...

"Dave" wrote in message
netamerica...
Attached is the schematic of the circuit I am working on, which is
basically a 555 timer running (IIRC) as a multivibrator, clocking the
4027 chip mentioned, which drives a simple transistor tester with Q1 and
not-Q1, and alternating the configuration of the tester with Q2. This is
the basic model, which I am trying to get working so I can expand it.
Frustration is, I had it working at one time, but can't remember what I
changed that made it stop working. It was constructed as shown on a
breadboard but got shoved up under the bed for a while due to more
pressing concerns. I am trying to dust it off, and pick it up again.
Any help would be greatly appreciated.

OPERATION is supposed to be as follows: Q1 and not-Q1 alternately bias
the transistor pluged into the E/B/C sockets as a PNP or NPN device,
indicating which polarity the device is by illuminating one of the two
LEDs in the schematic. When the transistor successfully turns on, it
shorts out one of the two LEDs, so that one LED flashing indicates the
polarity of the device under test. Two LEDs flashing mean no transistor,
or one that will not conduct when biased appropriately. Neither LED
flashing indicates a shorted transistor. And yes, it does work. PROBLEM
arises when I try to use the 74HC4053 in the lower left corner to change
the configuraton of the E/B/C sockets for a transistor with E/C/B pin
configuration (like an NTE199) rather than standard E/B/C pin
configuration (like a 2N3904 or 2N3906). To make this happen, I use Q2
to alternately send the "Select A/B/C" pins of the 74HC4053 high and low,
which alters which of the a/b/c (lowercase) pins are connected to the
A/B/C (uppercase) input/output pins that are in turn connected to the
E/BC sockets of the basic tester. And, yes, I can make this happen too.
But not with the shown schematic. To make this last part happen, I must
disconnect Q2 from the Select A/B/C pins, and connect not-Q2. With this
change the project tells me that the NTE199 under test is functional as
an NPN transistor. But it will not tell me anything about the 2N3904 or
the 2N3906. To re-establish that functionality, I must disconnect not-Q2
and reconnect Q2 to the Select A/B/C pins of the 74HC4053. And this, if
I am not mistaken, is *not* the way it is supposed to work. If I am to
understand correctly, Q2 going from high to low (logic 1 to logic 0?)
should do it all. Someone please enlighten me. What am I missing?

Ignorantly yours...

Dave

PS: For whatever mistakes I have made in my description of the circuit or
its operation, I can only ask patience. I am not a degreed individual
(nobody was wondering about that, right?) and I do not have any cookbooks
under my belt. I am merely a tinkerer trying to produce something
worthwhile. As I said before, any help is greatly appreciated.





A couple of observations-
The 555 used as an oscillator has a notorious glitch on the pin 3 output.
There are ways of dealing with this like putting a .01uF from pin 3 to
gnd. The other way is to disconnect R2 from pin 7 and take it instead to
pin 3. You can then take your output from pin 7. Pin 7 is the discharge
pin but it makes an equally good open collector drive. Since you have R1
as a pullup on this pin, you're good to go. Using pin 3 to drive the RC
works since it is a totem pole drive. The frequency and pulsewidth will be
a bit different but frequency is now set with one resistor...

Breadboards (protoboard) are very handy to use for trying things out but
awful for spurrious coupling. The rows of pins are separated from adjacent
rows by a thin spacer and make for capacitive coupling. This can really
mess up clocked devices. When in doubt, use a few hundred pF from the
clock line to gnd to test if it makes the problem go away.

See if this gets you going and then you can futz with the 4053.

Oppie
(been there, did that, bought the tee shirt)




BTW, thank you again, Oppie, for this info on 555 timers used as
oscillators. I'm copying it to my notes for future referrence.

Dave