My NE-2 Relaxation Oscillator is Too Relaxed ???

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I am experimenting with a relaxation oscillator circuit consisting of
a NE-2 bulb wired parallel to a capacitor and this pair is wired in
series with a resistor and connected across a 150 V DC power source (a
bunch of DC wallwarts connected in series). The resistor is variable
0-1 Meg Ohm, the capacitor is a 1uF electrolytic rated at 160V. I
don't have any capacitors on hand with a higher working voltage.

The circuit seems to work. I can get the bulb to blink around 3 times
a second but I am wanting a higher flash rate and I am not getting
it. Lowering the resistance makes the bulb turn on continuously. I
don't think that the bulb is flashing faster than the eye can
distinguish. I conneded the circuit to an oscilliscope and when the
bulfb is visually flashing I see the RC discharge curve but lowering R
until the bulf truns on continuously pretty much produces a flat line
on the scope.

I was expecting to maybe be able to get around 2-100 hz with a NE-2
relaxation oscillator. Is this possible or am I expecting too much
from this type of circuit? And if so, why?

Any help would be greatly appreciated. Thanks
 
On 7/2/08 4:14 PM, in article XXTak.3268$vn7.2496@flpi147.ffdc.sbc.com, "Bob
Eld" <nsmontassoc@yahoo.com> wrote:

jalbers@bsu.edu> wrote in message
news:2f8acf53-1cda-424c-9073-6706a1eb55ac@k37g2000hsf.googlegroups.com...
I am experimenting with a relaxation oscillator circuit consisting of
a NE-2 bulb wired parallel to a capacitor and this pair is wired in
series with a resistor and connected across a 150 V DC power source (a
bunch of DC wallwarts connected in series). The resistor is variable
0-1 Meg Ohm, the capacitor is a 1uF electrolytic rated at 160V. I
don't have any capacitors on hand with a higher working voltage.

The circuit seems to work. I can get the bulb to blink around 3 times
a second but I am wanting a higher flash rate and I am not getting
it. Lowering the resistance makes the bulb turn on continuously. I
don't think that the bulb is flashing faster than the eye can
distinguish. I conneded the circuit to an oscilliscope and when the
bulfb is visually flashing I see the RC discharge curve but lowering R
until the bulf truns on continuously pretty much produces a flat line
on the scope.

I was expecting to maybe be able to get around 2-100 hz with a NE-2
relaxation oscillator. Is this possible or am I expecting too much
from this type of circuit? And if so, why?

Any help would be greatly appreciated. Thanks

As mentioned above, use a much smaller capacitor. Also, never allow the
resistance to go near zero ohms as this can burn out the NE-2.

The Neon lamp is a negative resistance device. To oscillate it has to stay
in the negative resistance region. The pot is a positive or normal resistor.
If it's value is adjusted too low, the overall combination resistance
becomes positive, oscillation stops and the lamp turns full on. That's what
you are observing. Keep the resistor value high and the capacitor small.
Click to expand...
Actually, it's a relaxation oscillator. The lamp is off when the voltage
across the cap is less than the firing voltage (about 67 Volts for a NE2).
When the cap charges to around 67V, the neon ignites and the voltage across
the cap falls from the low resistance "short" and the cycle of
charge-fire-charge-fire continues, creating the typical sawtooth waveform.
 
On Wed, 2 Jul 2008 13:49:49 -0700 (PDT), "jalbers@bsu.edu"
<jalbers@bsu.edu> wrote:

I am experimenting with a relaxation oscillator circuit consisting of
a NE-2 bulb wired parallel to a capacitor and this pair is wired in
series with a resistor and connected across a 150 V DC power source (a
bunch of DC wallwarts connected in series). The resistor is variable
0-1 Meg Ohm, the capacitor is a 1uF electrolytic rated at 160V. I
don't have any capacitors on hand with a higher working voltage.

The circuit seems to work. I can get the bulb to blink around 3 times
a second but I am wanting a higher flash rate and I am not getting
it. Lowering the resistance makes the bulb turn on continuously. I
don't think that the bulb is flashing faster than the eye can
distinguish. I conneded the circuit to an oscilliscope and when the
bulfb is visually flashing I see the RC discharge curve but lowering R
until the bulf truns on continuously pretty much produces a flat line
on the scope.

I was expecting to maybe be able to get around 2-100 hz with a NE-2
relaxation oscillator. Is this possible or am I expecting too much
from this type of circuit? And if so, why?

Any help would be greatly appreciated. Thanks
Click to expand...
Smaller cap. Then, for fun, put two neons in parallel. Then try waving
hands around, shinging lights on them, whatever.

John
 
On Wed, 2 Jul 2008 16:14:01 -0700, "Bob Eld" <nsmontassoc@yahoo.com>
wrote:

jalbers@bsu.edu> wrote in message
news:2f8acf53-1cda-424c-9073-6706a1eb55ac@k37g2000hsf.googlegroups.com...
I am experimenting with a relaxation oscillator circuit consisting of
a NE-2 bulb wired parallel to a capacitor and this pair is wired in
series with a resistor and connected across a 150 V DC power source (a
bunch of DC wallwarts connected in series). The resistor is variable
0-1 Meg Ohm, the capacitor is a 1uF electrolytic rated at 160V. I
don't have any capacitors on hand with a higher working voltage.

The circuit seems to work. I can get the bulb to blink around 3 times
a second but I am wanting a higher flash rate and I am not getting
it. Lowering the resistance makes the bulb turn on continuously. I
don't think that the bulb is flashing faster than the eye can
distinguish. I conneded the circuit to an oscilliscope and when the
bulfb is visually flashing I see the RC discharge curve but lowering R
until the bulf truns on continuously pretty much produces a flat line
on the scope.

I was expecting to maybe be able to get around 2-100 hz with a NE-2
relaxation oscillator. Is this possible or am I expecting too much
from this type of circuit? And if so, why?

Any help would be greatly appreciated. Thanks

As mentioned above, use a much smaller capacitor. Also, never allow the
resistance to go near zero ohms as this can burn out the NE-2.

The Neon lamp is a negative resistance device. To oscillate it has to stay
in the negative resistance region.
Click to expand...
---
Not true.

It exhibits negative resistance characteristics over its glow range,
but in order to work as a gross relaxation oscillator it has to break
out of the negative resistance region by discharging the parallel
capacitor through the plasma to the point where it can no longer
support conduction and then return to the more-or-less deinozed state
where the glow is extinguished and the cycle is started anew with the
capacitor charging up to the ionization voltage.
---

The pot is a positive or normal resistor.
If it's value is adjusted too low, the overall combination resistance
becomes positive, oscillation stops and the lamp turns full on. That's what
you are observing. Keep the resistor value high and the capacitor small.
Click to expand...
---
Good advice, but the deionization time of the gas in the tube will be
the ultimate determinant of the relaxation oscillator's high
frequency.

JF
 
On 7/2/08 7:06 PM, in article zuWak.31133$ZE5.5572@nlpi061.nbdc.sbc.com,
"Bob Eld" <nsmontassoc@yahoo.com> wrote:

"Don Bowey" <dbowey@comcast.net> wrote in message
news:C4916A23.BD130%dbowey@comcast.net...
On 7/2/08 4:14 PM, in article XXTak.3268$vn7.2496@flpi147.ffdc.sbc.com,
"Bob
Eld" <nsmontassoc@yahoo.com> wrote:


jalbers@bsu.edu> wrote in message

news:2f8acf53-1cda-424c-9073-6706a1eb55ac@k37g2000hsf.googlegroups.com...
I am experimenting with a relaxation oscillator circuit consisting of
a NE-2 bulb wired parallel to a capacitor and this pair is wired in
series with a resistor and connected across a 150 V DC power source (a
bunch of DC wallwarts connected in series). The resistor is variable
0-1 Meg Ohm, the capacitor is a 1uF electrolytic rated at 160V. I
don't have any capacitors on hand with a higher working voltage.

The circuit seems to work. I can get the bulb to blink around 3 times
a second but I am wanting a higher flash rate and I am not getting
it. Lowering the resistance makes the bulb turn on continuously. I
don't think that the bulb is flashing faster than the eye can
distinguish. I conneded the circuit to an oscilliscope and when the
bulfb is visually flashing I see the RC discharge curve but lowering R
until the bulf truns on continuously pretty much produces a flat line
on the scope.

I was expecting to maybe be able to get around 2-100 hz with a NE-2
relaxation oscillator. Is this possible or am I expecting too much
from this type of circuit? And if so, why?

Any help would be greatly appreciated. Thanks

As mentioned above, use a much smaller capacitor. Also, never allow the
resistance to go near zero ohms as this can burn out the NE-2.

The Neon lamp is a negative resistance device. To oscillate it has to
stay
in the negative resistance region. The pot is a positive or normal
resistor.
If it's value is adjusted too low, the overall combination resistance
becomes positive, oscillation stops and the lamp turns full on. That's
what
you are observing. Keep the resistor value high and the capacitor small.



Actually, it's a relaxation oscillator. The lamp is off when the voltage
across the cap is less than the firing voltage (about 67 Volts for a NE2).
When the cap charges to around 67V, the neon ignites and the voltage
across
the cap falls from the low resistance "short" and the cycle of
charge-fire-charge-fire continues, creating the typical sawtooth waveform.

That's the definition of negative resistance. When the voltage is high the
current is low or off and when the voltage is low, the current is high.
That's the opposite of a normal resistor where current goes up with voltage.
Relaxation cannot occur without negative resistance.

BTW it's possible to make a similar device with two transistors that will
work on a few volts.

Another ancient device that exhibits this characteristic is a tunnel diode.
GHz oscillators can be made with them.

Look up unijunction trasistor and diac, other devices that exhibit this
characteristic.


Perhaps you could post a link that plots the negative resistance region of
Click to expand...
a neon lamp?
 
On Wed, 02 Jul 2008 22:44:53 -0700, Don Bowey <dbowey@comcast.net>
wrote:

On 7/2/08 7:06 PM, in article zuWak.31133$ZE5.5572@nlpi061.nbdc.sbc.com,
"Bob Eld" <nsmontassoc@yahoo.com> wrote:


"Don Bowey" <dbowey@comcast.net> wrote in message
news:C4916A23.BD130%dbowey@comcast.net...
On 7/2/08 4:14 PM, in article XXTak.3268$vn7.2496@flpi147.ffdc.sbc.com,
"Bob
Eld" <nsmontassoc@yahoo.com> wrote:


jalbers@bsu.edu> wrote in message

news:2f8acf53-1cda-424c-9073-6706a1eb55ac@k37g2000hsf.googlegroups.com...
I am experimenting with a relaxation oscillator circuit consisting of
a NE-2 bulb wired parallel to a capacitor and this pair is wired in
series with a resistor and connected across a 150 V DC power source (a
bunch of DC wallwarts connected in series). The resistor is variable
0-1 Meg Ohm, the capacitor is a 1uF electrolytic rated at 160V. I
don't have any capacitors on hand with a higher working voltage.

The circuit seems to work. I can get the bulb to blink around 3 times
a second but I am wanting a higher flash rate and I am not getting
it. Lowering the resistance makes the bulb turn on continuously. I
don't think that the bulb is flashing faster than the eye can
distinguish. I conneded the circuit to an oscilliscope and when the
bulfb is visually flashing I see the RC discharge curve but lowering R
until the bulf truns on continuously pretty much produces a flat line
on the scope.

I was expecting to maybe be able to get around 2-100 hz with a NE-2
relaxation oscillator. Is this possible or am I expecting too much
from this type of circuit? And if so, why?

Any help would be greatly appreciated. Thanks

As mentioned above, use a much smaller capacitor. Also, never allow the
resistance to go near zero ohms as this can burn out the NE-2.

The Neon lamp is a negative resistance device. To oscillate it has to
stay
in the negative resistance region. The pot is a positive or normal
resistor.
If it's value is adjusted too low, the overall combination resistance
becomes positive, oscillation stops and the lamp turns full on. That's
what
you are observing. Keep the resistor value high and the capacitor small.



Actually, it's a relaxation oscillator. The lamp is off when the voltage
across the cap is less than the firing voltage (about 67 Volts for a NE2).
When the cap charges to around 67V, the neon ignites and the voltage
across
the cap falls from the low resistance "short" and the cycle of
charge-fire-charge-fire continues, creating the typical sawtooth waveform.

That's the definition of negative resistance. When the voltage is high the
current is low or off and when the voltage is low, the current is high.
That's the opposite of a normal resistor where current goes up with voltage.
Relaxation cannot occur without negative resistance.

BTW it's possible to make a similar device with two transistors that will
work on a few volts.

Another ancient device that exhibits this characteristic is a tunnel diode.
GHz oscillators can be made with them.

Look up unijunction trasistor and diac, other devices that exhibit this
characteristic.


Perhaps you could post a link that plots the negative resistance region of
a neon lamp?
Click to expand...
---
news:lnpp64t1q9ohk1d1ar57dhd673pmaif3g6@4ax.com

JF
 
On 7/3/08 7:53 AM, in article 8spp64hncghn88d0gqbensnerupo39h4k0@4ax.com,
"John Fields" <jfields@austininstruments.com> wrote:

On Wed, 02 Jul 2008 22:44:53 -0700, Don Bowey <dbowey@comcast.net
wrote:

On 7/2/08 7:06 PM, in article zuWak.31133$ZE5.5572@nlpi061.nbdc.sbc.com,
"Bob Eld" <nsmontassoc@yahoo.com> wrote:


"Don Bowey" <dbowey@comcast.net> wrote in message
news:C4916A23.BD130%dbowey@comcast.net...
On 7/2/08 4:14 PM, in article XXTak.3268$vn7.2496@flpi147.ffdc.sbc.com,
"Bob
Eld" <nsmontassoc@yahoo.com> wrote:


jalbers@bsu.edu> wrote in message

news:2f8acf53-1cda-424c-9073-6706a1eb55ac@k37g2000hsf.googlegroups.com...
I am experimenting with a relaxation oscillator circuit consisting of
a NE-2 bulb wired parallel to a capacitor and this pair is wired in
series with a resistor and connected across a 150 V DC power source (a
bunch of DC wallwarts connected in series). The resistor is variable
0-1 Meg Ohm, the capacitor is a 1uF electrolytic rated at 160V. I
don't have any capacitors on hand with a higher working voltage.

The circuit seems to work. I can get the bulb to blink around 3 times
a second but I am wanting a higher flash rate and I am not getting
it. Lowering the resistance makes the bulb turn on continuously. I
don't think that the bulb is flashing faster than the eye can
distinguish. I conneded the circuit to an oscilliscope and when the
bulfb is visually flashing I see the RC discharge curve but lowering R
until the bulf truns on continuously pretty much produces a flat line
on the scope.

I was expecting to maybe be able to get around 2-100 hz with a NE-2
relaxation oscillator. Is this possible or am I expecting too much
from this type of circuit? And if so, why?

Any help would be greatly appreciated. Thanks

As mentioned above, use a much smaller capacitor. Also, never allow the
resistance to go near zero ohms as this can burn out the NE-2.

The Neon lamp is a negative resistance device. To oscillate it has to
stay
in the negative resistance region. The pot is a positive or normal
resistor.
If it's value is adjusted too low, the overall combination resistance
becomes positive, oscillation stops and the lamp turns full on. That's
what
you are observing. Keep the resistor value high and the capacitor small.



Actually, it's a relaxation oscillator. The lamp is off when the voltage
across the cap is less than the firing voltage (about 67 Volts for a NE2).
When the cap charges to around 67V, the neon ignites and the voltage
across
the cap falls from the low resistance "short" and the cycle of
charge-fire-charge-fire continues, creating the typical sawtooth waveform.

That's the definition of negative resistance. When the voltage is high the
current is low or off and when the voltage is low, the current is high.
That's the opposite of a normal resistor where current goes up with voltage.
Relaxation cannot occur without negative resistance.

BTW it's possible to make a similar device with two transistors that will
work on a few volts.

Another ancient device that exhibits this characteristic is a tunnel diode.
GHz oscillators can be made with them.

Look up unijunction trasistor and diac, other devices that exhibit this
characteristic.


Perhaps you could post a link that plots the negative resistance region of
a neon lamp?

---
news:lnpp64t1q9ohk1d1ar57dhd673pmaif3g6@4ax.com

JF
Click to expand...
Thanks.

I had already thought more about the neon lamp and decided it could have, or
appear to have, a negative resistance region, so I did some google work and
found several trustworthy articles supporting it. I also found one credible
article saying the effect is not negative resistance, but...... If it quacks
like a duck it's probably a duck.

IMHO the typical neon tube relaxation "oscillator" does not use that effect,
however, but uses the gross cap discharge to begin a next charge cycle. The
external R must be high enough to allow the voltage across the tube to fall
far enough to extinguish the lamp.

This will be a good slow-day plaything. I think I'll put a parallel
resonant circuit in series with the lamp and variable voltage source.......
 
On Thu, 03 Jul 2008 08:57:48 -0700, Don Bowey <dbowey@comcast.net>
wrote:

On 7/3/08 7:53 AM, in article 8spp64hncghn88d0gqbensnerupo39h4k0@4ax.com,
"John Fields" <jfields@austininstruments.com> wrote:

On Wed, 02 Jul 2008 22:44:53 -0700, Don Bowey <dbowey@comcast.net
wrote:

Perhaps you could post a link that plots the negative resistance region of
a neon lamp?

---
news:lnpp64t1q9ohk1d1ar57dhd673pmaif3g6@4ax.com

JF

Thanks.

I had already thought more about the neon lamp and decided it could have, or
appear to have, a negative resistance region, so I did some google work and
found several trustworthy articles supporting it. I also found one credible
article saying the effect is not negative resistance, but...... If it quacks
like a duck it's probably a duck.

IMHO the typical neon tube relaxation "oscillator" does not use that effect,
however, but uses the gross cap discharge to begin a next charge cycle.
Click to expand...
---
I agree, and stated that in an earlier post. :)
---

The external R must be high enough to allow the voltage across the tube to fall
far enough to extinguish the lamp.
Click to expand...
---
Yes, and when the gas in the tube deionizes to the point where current
through it falls to a low enough level, the "striking voltage" must
then be raised high enough to once again start the ionization.
---

This will be a good slow-day plaything. I think I'll put a parallel
resonant circuit in series with the lamp and variable voltage source.......
Click to expand...
---
Sounds like fun. :)

If you want to you can go here:

http://www.duntemann.com/12vtubes/datasheetsindex.htm

and download all 80 megabytes (!) of the GE glow lamp manual.

JF
 
On Wed, 02 Jul 2008 13:49:49 -0700, jalbers@bsu.edu wrote:

I am experimenting with a relaxation oscillator circuit consisting of a
NE-2 bulb wired parallel to a capacitor and this pair is wired in series
with a resistor and connected across a 150 V DC power source (a bunch of
DC wallwarts connected in series). The resistor is variable 0-1 Meg Ohm,
the capacitor is a 1uF electrolytic rated at 160V. I don't have any
capacitors on hand with a higher working voltage.
Click to expand...
I also vote "smaller cap", but I'd add to this: There should be a 220K or
so (I wouldn't go below about 180K) in series with the pot so that when
you turn the pot down, you don't burn out the bulb. I guess you'd size the
R so that with your supply you'd want to limit the neon current to the
~1-2 mA range.

Have Fun!
Rich
 
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