Chip with simple program for Toy

"Sjouke Burry" <burrynulnulfour@ppllaanneett.nnlll> wrote in message
news:486a9987$0$6005$ba620dc5@text.nova.planet.nl...
rabiticide wrote:
uh. no sloshing, and i didn't turn it upside down. It seemed pretty
dry. I moved it side to side briskly and neither felt nor heard
anything "slosh". But how else would this be explained? Is H2SO4
pretty viscous?


rK
a bit oily.

I wonder what substance they use in jelly-electrolyte lead-acid cells ... to
suspend the acid in a jelly.

Chris
 
<mrdarrett@gmail.com> wrote in message
news:1e6e5d05-ed46-4ff7-a246-35a18c841cd1@i18g2000prn.googlegroups.com...
On Jul 1, 3:07 pm, John Fields <jfie...@austininstruments.com> wrote:
On Tue, 1 Jul 2008 13:30:05 -0700 (PDT), mrdarr...@gmail.com wrote:
On Jul 1, 12:15 pm, John Fields <jfie...@austininstruments.com> wrote:
On Tue, 1 Jul 2008 11:55:35 -0700 (PDT), mrdarr...@gmail.com wrote:
On Jul 1, 11:48 am, Don Bowey <dbo...@comcast.net> wrote:
On 7/1/08 11:30 AM, in article
a1662fad-e0d7-4306-9e20-195abb1e7...@c19g2000prf.googlegroups.com,

"mrdarr...@gmail.com" <mrdarr...@gmail.com> wrote:
I was reading the datasheet for the LM1875
http://www.national.com/ds.cgi/LM/LM1875.pdf

and I noticed that they do have a schematic for a single supply (as
opposed to a +/- supply).

If running on a single supply, does the chip amplifer consume
significant power during quiet tracks?

Would this be pretty much the same as running the amplifier in Class A
mode (vs. Class AB)?

I'm trying to figure out if I really need a +/- power supply, or if I
can just go with a single supply (easier to build).

Thanks,

Michael

The datasheet does have a "Typical Single Supply Operation" schematic.
Have another look.

Yes, that's what I said. There is a schematic. It's on Page 2.
(amused grin)

---
Look at "Supply Current" on page 2 and read: "Power Dissipation and
Heat Sinking" on page 6.

JF

Ah, so apparently the chip does not use more power with a single
supply than with a +/- supply.

Is there any reason why I should NOT use a single supply with this
chip?

---
I don't think so, but try it and see if it works the way you want it
to. If it does you've saved a supply, but if it doesn't it's only
cost you a handful of discretes.

JF


Good point. Thanks.

Michael
I would like to point out that the single supply schematic has a 2200 uF
capacitor in series with the output speaker. In theory, with an ideal
capacitor, this is going to give an 18 Hz cutoff frequency into a 4 ohm
speaker (36 Hz into 8 ohms). A real capacitor will have some internal
resistance. This is going to give a higher cutoff frequency.
 
"George Jetson" <GeorgeJetson@spacely.com> wrote in message
news:HDuak.15996$Ri.13241@flpi146.ffdc.sbc.com...
"Jonathan Kirwan" <jkirwan@easystreet.com> wrote in message
news:1cui64tp3blo98q3cuekdkbq8mqm64sgnv@4ax.com...
On Mon, 30 Jun 2008 17:06:09 -0700 (PDT), rabiticide
rabiticide@gmail.com> wrote:

It's my motorcycle battery and it's the situation where I need it to
get to this job so I can afford to fix it. I just came off disability
and with $4 to my name I spent $2 on a gallon of distilled water...

Okay. It sounded like that kind of situation. I've been there in my
life, too, so I can feel your pain.

So I am going to try it and see what happens. I will post my
results....

If there doesn't appear to be _any_ sulfuric acid inside, then I don't
hold out much hope here. But best luck, anyway.

Isn't H2SO4 a solid? I don't know - I'm thinking of, like, NaOH which
dissolves in water to make the base.
snip

NaOH is a solid. White, and kind of slippery to the touch. But
sulfuric acid is a liquid. I've used it, before, as part of a double
boiler situation that could achieve the higher melting points I needed
at the time while also providing very, very even heating which was
also necessary for the rocket fuel I was making then.

Jon

Depending on local weather conditions, rain water should woek as well.

--
They can have my command prompt when they pry it from my cold dead
fingers.
Rain water is not clean. It has a nucleus of something and collects crap on
the way down.

Tom
 
<mrdarrett@gmail.com> wrote in message
news:a1662fad-e0d7-4306-9e20-195abb1e7311@c19g2000prf.googlegroups.com...
I was reading the datasheet for the LM1875
http://www.national.com/ds.cgi/LM/LM1875.pdf

and I noticed that they do have a schematic for a single supply (as
opposed to a +/- supply).

If running on a single supply, does the chip amplifer consume
significant power during quiet tracks?

Would this be pretty much the same as running the amplifier in Class A
mode (vs. Class AB)?

I'm trying to figure out if I really need a +/- power supply, or if I
can just go with a single supply (easier to build).

Thanks,

Michael
Since the LM1875 is inexpensive, you might try using two of them on a
single supply, and putting the speaker between the outputs. You would have
to make one amp inverting and the other non-inverting, but you will get
twice the output voltage and save the capacitors. A single 24 volt supply
will then give +/- 24 volts, or about 17 VRMS, to an 8 ohm speaker, or 36
watts. There are lots of 24 VDC supplies available. The downside of this
approach is making sure the DC level of both amps are equal and about 1/2
the supply.

If you check SemiElectric's eBay store you will find PC boards and kits for
the LM3875, as well as other single and dual amplifier ICs:

http://search.stores.ebay.com/semielectric_audio-amp_W0QQfciZQ2d1QQfclZ3QQfsnZsemielectricQQfsooZ2QQfsopZ3QQfsubZ0QQsaselZ650588702QQsofpZ0

His LM3875s are about $6.50 each. They are larger (56 watts vs 20 watts),
but seem to be otherwise quite similar. Most of the additional IC pins are
NCs, for heat sinking and mechanical mounting, I suppose. They are only
$5.90 each from DigiKey, and the LM1875 is $3.28. Wow: 10 to 15 cents per
watt!

Paul
 
On Tue, 1 Jul 2008 13:48:57 +0100, Paul Carpenter
<paul@pcserviceselectronics.co.uk> wrote:

In article <486a101e.590892@news.sysmatrix.net>, NoSpam@daqarta.com
says...

Incandescent bulbs may be hazardous as well: Animal studies of
tungsten shrapnel show that it is a very powerful carcinogen. I don't
know how tungsten dust (which I assume must be inside the envelope
after the filament burns out) would behave in the lungs, but I suspect
the answer would be "not good".

Considering the original quantity of tungsten, and distribution of
'shrapnel', you have a low probability of ingest (stomach/lungs) enough
tungsten to be more than a minor irritant. From recollection it is
difficult to absorb tungsten through skin contact.
As I recall, the animal studies used tiny particles of tungsten. The
tumors were formed directly at the point of skin contact... no
absorption needed. (I believe they "implanted" the particles through
tiny incisions to hold them just under the skin surface.) But the
alarming thing was that the particles were pretty much 100% effective
at causing tumors... not like "increases the risk of", as we see for
things like smoking or radon.

Best regards,




Bob Masta

DAQARTA v4.00
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
FREE Signal Generator
Science with your sound card!
 
On Tue, 1 Jul 2008 10:15:55 -0700 (PDT), Kasterborus
<kasterborus@yahoo.com> wrote:

Hi,

I'm looking for a circuit that can read a standard line level audio
signal and output a continous voltage 0-5v proportional to the
amplitude of the input.

This in turn would be read by an ADC/microprocessor to modulate some
flashing lights.

As always - any help is greatly appreciated.
If you are going to use an ADC and microprocessor anyway, you might
want to consider letting them do more of the work. You could provide
a preamp to get the signal in range of the ADC, and let software do
the rest.

That way , the software can handle attack/decay time constants, and
most importantly it can do FFT spectral analysis to get frequency
information, if you later decide you want it.

Of course, this will mean that you will need to sample at a much
higher rate and deal with the flow of data. You don't mention the
capabilities of the uP you have in mind... can it handle this kind of
workload?

Best regards,


Bob Masta

DAQARTA v4.00
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Scope, Spectrum, Spectrogram, Sound Level Meter
FREE Signal Generator
Science with your sound card!
 
<mrdarrett@gmail.com> wrote in message
news:fd4d48c0-8c69-4c14-b6c9-f090c696beaf@i18g2000prn.googlegroups.com...
Is it standard that a TO-220 transistor package is, with the tab up,
with the markings facing you, Base, Collector, Emitter? (for example,
on the TIP31A)

I noticed the TO-92 2N3904 I have is (with the markings facing me) E B
C, and a TO-92 2N2222 data sheet even shows C B E !!!

Michael
The TO-220 package is used for many devices not just transistors.
The pinout is what the data sheet says it is.
Always consult the data sheet if the leads are not marked.

Tom
 
<mrdarrett@gmail.com> wrote in message
news:1308fc94-659e-4818-898d-bd2830be9198@u12g2000prd.googlegroups.com...
On Jul 2, 10:32 am, "Tom Biasi" <tombiasi...@optonline.net> wrote:
mrdarr...@gmail.com> wrote in message

news:fd4d48c0-8c69-4c14-b6c9-f090c696beaf@i18g2000prn.googlegroups.com...

Is it standard that a TO-220 transistor package is, with the tab up,
with the markings facing you, Base, Collector, Emitter? (for example,
on the TIP31A)

I noticed the TO-92 2N3904 I have is (with the markings facing me) E B
C, and a TO-92 2N2222 data sheet even shows C B E !!!

Michael

The TO-220 package is used for many devices not just transistors.
The pinout is what the data sheet says it is.
Always consult the data sheet if the leads are not marked.

Tom



So does this mean it is NOT standard that a TO-220 *transistor*
package is BCE? (with the markings facing you)

Michael
You will find some that are not that way.

Tom
 
<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
Try a smaller capacitor e.g. 0.47uF
 
"Kasterborus" <kasterborus@yahoo.com> wrote in message
news:991686a5-accb-4b91-bf75-f676f51c28c7@r66g2000hsg.googlegroups.com...
Hi,

I'm looking for a circuit that can read a standard line level audio
signal and output a continous voltage 0-5v proportional to the
amplitude of the input.

This in turn would be read by an ADC/microprocessor to modulate some
flashing lights.

As always - any help is greatly appreciated.

Dave
Since you are going to ADC it anyway, simply capacitivly couple the audio
signal into the ADC. Insure that the max peak of the audio signal is within
the ADC range.

Convert to digital then detect and hold the maximum values for a determined
length of time. Use the numerical value in this hold register to control
what ever.

Each converted value is compared with the previously held value and updates
the held value if larger. A timer starts or restarts on each hold update.
The register is cleared on the expiration of the timer. This creates a
running peak of the audio signal.

The peaks values of most audio signals will be emphasized in the bass
region. This can be tailored with simple filtering if needed which isn't
likely.
 
<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.
 
"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.
 
"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:486C1510.E1D699E3@hotmail.com...
Bob Eld wrote:

Insure that the max peak of the audio signal is within
the ADC range.

Diode clamp it !

Graham

Yeah you can clamp it but then you loose that and higher values as peaks.
The whole idea is to convert the peaks to numbers not to clip them off.

There's really no need to clamp it. The processor input will have internal
"diodes" that will keep the voltage from exceeding the rail voltage plus a
little. Likewise the input voltage won't go below ground. A series
resistance should be added to limit the input current and a shunt resistance
added to keep the DC level from shifting up due to rectification by these
clamps.
 
<jalbers@bsu.edu>

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?

** The neon's conduction current must be able to reduce the voltage on the
cap to below the neon's extinguishing voltage in order for there to be
oscillations.

If the series resistor is too low in value - this will not happen.

So use a small cap - like 10nF and try again.



....... Phil
 
<jalbers@bsu.edu> schreef in bericht
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
You'd first of all read the specifications of the NE-2. Like a lot of neon
bulbs it ignites at about 90V. It is the rating for DC but that's half the
truth. It will ignite when the voltage accross its leads reaches that 90V.
That's where the 65Vac comes from. A 65Vac RMS sine will peak at about 90V.

Once the bulb has ignited, the voltage accross its leads sinks to about 60V,
regardless of the current. So you have to make a provision to keep the
average current at or below 0.5mA where it is rated for. More current will
reduce the lifetime of the bulb or may even destroy it. The bulb will
extinguish when the voltage across its leads sinks below 60V. You may not
find this 60V in the specifications as this value varies. Most of the times
it is not specified at all.

So the mecanism of a relaxation oscillator will be clear. The capacitor is
charged via the resistor. Once the voltage reaches 90V the bulb ignites and
discharges the capacitor until the voltages sinks to about 60V. Then the
bulb extinguishes and the capacitor will start to charge again.

But... once the bulb has ignited, the current through the resistor adds up
with the discharge current of the capacitor. If that "resistor" current is
enough to keep the bulb going, it will not extinguish. So you cannot lower
the resistor too much as it controlls the current.

The frequency of your oscillator depends on the resistor and the capacitor
value. They determine the time required to charge the capacitor from 60V to
90V. Once the bulb ignites, discharging goes fast. This time can be
neglected with respect to the charging time.

So once you reaches the lowest value of the resistor, you can only lower the
capacitor value to raise the frequency. Using the right components,
frequencies of several kHz should be possible.

petrus bitbyter
 
"Eeyore" <rabbitsfriendsandrelations@hotmail.com> wrote in message
news:486C4867.F6DAF534@hotmail.com...
Bob Eld wrote:

"Eeyore" wrote
Bob Eld wrote:

Insure that the max peak of the audio signal is within
the ADC range.

Diode clamp it !

Graham

Yeah you can clamp it but then you loose that and higher values as
peaks.
The whole idea is to convert the peaks to numbers not to clip them off.

You can actively diode clamp. Just don't want to hurt the poor ADC 'just
in
case'. I doubt that for flickering lights, losing anything below say 0x240
will
hurt any


There's really no need to clamp it. The processor input will have
internal
"diodes" that will keep the voltage from exceeding the rail voltage
plus a
little.

A discussion we've had many a time before here !


Likewise the input voltage won't go below ground.

It WON'T ? In what ideal world is this ?


A series resistance should be added to limit the input current and a
shunt
resistance
added to keep the DC level from shifting up due to rectification by
these
clamps.

Uh ?

Graham
Well, if there is an internal diode from the input to the negative rail, it
will keep the voltage on the input from going below ground, ignoring the
diode drop, of course.

Now, if you capacitively couple to the input, this diode will rectify the
negative going portion of the audio signal and charge the capacitor,
positive towards the input. This will offset the zero base line in the
positive direction and screw up the peak detection. A judicious resistance
to ground with an appropriate series resistance will limit the current and
drain off this offsetting charge. It ain't rocket surgery!
 
ive been there with my bike, boild my battery dry
every time i refill it, i found it was the bikes
regulator was faulty.

"rabiticide" <rabiticide@gmail.com> wrote in message
news:0b9bdaa6-84d6-4b39-b64f-85ab5e295a77@w1g2000prd.googlegroups.com...
I was charging my battery over the weekend and checked it last night
to find the battery dead as a doornail. Upon examination, the battery
is completely dry. I'm guessing it was overcharged and the water
boiled away but it shouldn't've 'cause it's an "automatic battery
charger" that's designed to stop charging when it's done...

So, do I just add distilled H2O? Will that work? I have to walk to the
store 1.5 miles (2.5 km) away and that's a long way to carry 1 gallon
(4? L) of water...


rK
 
<mrdarrett@gmail.com> wrote in message
news:7edf1122-2064-4799-9661-4828c556a5ce@s21g2000prm.googlegroups.com...
I built an astable multivibrator with blinking lights (much simpler
than using a 556!), as a test for a circuit that will use a power
transistor (or MOSFET) to pulse a transformer primary for future
experiments.

http://mrdarrett.googlepages.com/blinkenlights002.pdf

Strangely, when I replaced the two 2N3904 transistors with TIP31As,
the circuit would not oscillate unless I briefly disconnected then re-
connected R2 or R3. (I bumped the voltage up from 3V to 6V during
these tests.)

As a work-around, I'm considering just putting the 2N3904s back in,
and connecting the positive end of C2 to the base of a TIP31A.
Inelegant, but I think it will work.

I'm trying to figure out why TIP31As won't work, but it also doesn't
help me any that the TIP31A data sheet does not specify a minimum
V_BE_on.

http://www.st.com/stonline/products/literature/ds/12292/tip31a.pdf

Input?

Michael
One possible reason it doesn't work with certain transistors is that the two
transistors come on together and lock up the operation. It fails to
flip-flop. Also, there might not be enough base current for TIP31's with R2
and R3 at 10K. Lower these resistors. The minimum beta is 25 at 1 amp. so
you're likely not getting enough current to drive these transistors.

To insure that an astable won't lock up, disconnect R2 and R3 from the
positive rail and connect the junction of the two resistors to the cathodes
of two diodes. Connect the anodes of the diodes to the anodes of the LED's,
one on each.

With this arrangement, if the transistors both come on together, the base
drive is reduced and the circuit will always start.
 
<mrdarrett@gmail.com> wrote in message
news:a731e6f8-d541-4301-9959-88d1f7d9106b@q27g2000prf.googlegroups.com...
On Jul 3, 6:54 pm, "Bob Eld" <nsmontas...@yahoo.com> wrote:
mrdarr...@gmail.com> wrote in message

news:7edf1122-2064-4799-9661-4828c556a5ce@s21g2000prm.googlegroups.com...



I built an astable multivibrator with blinking lights (much simpler
than using a 556!), as a test for a circuit that will use a power
transistor (or MOSFET) to pulse a transformer primary for future
experiments.

http://mrdarrett.googlepages.com/blinkenlights002.pdf

Strangely, when I replaced the two 2N3904 transistors with TIP31As,
the circuit would not oscillate unless I briefly disconnected then re-
connected R2 or R3. (I bumped the voltage up from 3V to 6V during
these tests.)

As a work-around, I'm considering just putting the 2N3904s back in,
and connecting the positive end of C2 to the base of a TIP31A.
Inelegant, but I think it will work.

I'm trying to figure out why TIP31As won't work, but it also doesn't
help me any that the TIP31A data sheet does not specify a minimum
V_BE_on.

http://www.st.com/stonline/products/literature/ds/12292/tip31a.pdf

Input?

Michael

One possible reason it doesn't work with certain transistors is that the
two
transistors come on together and lock up the operation. It fails to
flip-flop. Also, there might not be enough base current for TIP31's
with R2
and R3 at 10K. Lower these resistors. The minimum beta is 25 at 1 amp.
so
you're likely not getting enough current to drive these transistors.

To insure that an astable won't lock up, disconnect R2 and R3 from the
positive rail and connect the junction of the two resistors to the
cathodes
of two diodes. Connect the anodes of the diodes to the anodes of the
LED's,
one on each.

With this arrangement, if the transistors both come on together, the
base
drive is reduced and the circuit will always start.
I tried simulating various forms of this circuit with both 2N3904 and
2N3055, and it always seemed to work, at least down to 2.5 volts or so. It
seemed to woek better if I connected C1 and C2 directly to the collectors,
which have a bit more voltage swing. I would suggest connecting a logic
level MOSFET to drive a transformer, so you will have minimal loading.
Without the LEDs, you will have plenty of voltage swing for the gate. And
you can use an N-channel to sink a higher voltage on a transformer CT, or
P-channel to source the voltage. You might even be able to make a full
bridge, but you need to make sure there is dead time where both the
high-side and low side are off. This is why they have dedicated circuits
for that.

Paul
 
<angus.oliver@gmail.com> wrote in message
news:11cf7b47-7d56-412a-99c8-f738cd2936b9@h1g2000prh.googlegroups.com...
Hi All,

Having found dual op amp packages around a fifth the price of
comparable single packages from online distributors, I think i'll go
for the double.
(BTW, I'm using supply of +16, and ground).

I don't want the unused channel drawing current unnecessarily though,
or bouncing the output around.. - If I tie the non-inverting input to
+3.3V, and have a high resistance feedback resistor to the inverting
input (with no other input to that pin), would that be as good as
anything? I figure the output won't have to 'try' very hard to modify
the voltage of an input pin with no other voltages on it..

Am I right?

Thanks..
Just tie the inverting input to the output, unity gain. Three point three
volts on the noninverting input is OK. You can usually just ground this
point, in this case connecting it to the negative rail. Ideally the common
mode range of the input should include the negative rail but that may not be
necessary depending on the particular amp.
 

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